Ensuring the safety of heating equipment operating on gas is one of the most important tasks facing designers and operating personnel of boiler houses.
Solving this problem in practice is complicated by the wear and tear of the equipment, its physical and moral aging, the malfunction of individual elements of automation equipment, as well as the insufficiently high level of qualifications and low technological discipline of the operating personnel, which can lead to serious accidents accompanied by casualties.
Investigation of emergency situations, especially those related to safety devices, is often difficult due to the lack of objective information about the reasons that led to their occurrence.
One of the most important elements, the condition of which largely determines the level of safety of gas boiler houses, is the purge valve of the gas manifold.
Leakage of the purge valve shutter is one of the reasons for gas leakage (losses) through the purge gas pipeline into the atmosphere, and if there is a malfunction of other gas elements shut-off valves creates dangerous preconditions for unauthorized entry of gas into production premises and boiler furnaces.
Existing automation system designs do not provide for the possibility of continuous monitoring of the purge valve tightness.
We witnessed the accidental discovery of a leak in the purge valve of the gas manifold, when at the stage of commissioning, while checking the automatic ignition system of a backup boiler unit with the igniter solenoid valve turned off, after a spark was supplied, a steady burning of the igniter torch occurred. The boiler room maintenance personnel did not have the information to promptly detect this malfunction and take the necessary measures to eliminate it.
In order to prevent such situations, it is proposed to install a glass water seal filled with
glycerin. The control circuit consists of a gas manifold pipeline, a gas valve 1, a purge valve 2, a water seal 3, and a filler neck 5.
Gas valve 1 is necessary if the purge valve is missed during operation of the boiler unit, as well as when inspecting or replacing the valve. Gas passage is determined by bubbles in the water seal during purging and operation of the boiler unit.
If the first magnetic valve is leaking, gas leakage can be seen in the form of bubbles that rise in the liquid when the burner is at rest.
If the purge valve leaks during burner operation.
The device is designed in such a way that when gas pressure changes, glycerin does not penetrate into the pipeline.
Another advantage of this device is that the section of pipeline between the valves does not fill with air during long periods of inactivity.
The proposed technical solution contains known elements and can be implemented on the basis of standard industrial devices. The costs of implementing the proposed technical solution are insignificant and incommensurate with the losses that may arise as a result emergency situation caused by a leak in the gas manifold purge valve.
Head of the non-destructive testing laboratory of Kontakt LLC Konstantin Borisovich Ktitrov
Head of the department for electrical safety of ZiS LLC "Contact" Melnikov Lev Mikhailovich
Engineer 1st category of Kontakt LLC Katrenko Vadim Fedorovich
Engineer-expert of Kontakt LLC Keleberda Alexander Ivanovich
Expert of Kontakt LLC Kuznetsov Viktor Borisovich
One of the ways to solve the problem of automating the tightness control of hollow products, for example, shut-off valves, is to develop a multi-position adjustable stand for automatic control of the tightness of products with compressed air, using the manometric method. There are many designs of such devices. An automatic product seal control device is known, containing a table with a drive, an elastic sealing element, a rejecting device, a source of compressed gas, a copier and a device for clamping the product.
However, process automation is achieved due to the significant complexity of the machine design, which reduces the reliability of its operation.
An automatic machine for monitoring the tightness of hollow products is known, containing sealing units with leakage sensors, a test gas supply system, product movement mechanisms and a rejection mechanism.
The disadvantage of this machine is the complexity of the technological process for monitoring the tightness of products and low productivity.
Closest to the invention is a stand for testing products for leaks, containing a rotor, a drive for its stepwise movements, control blocks placed on the rotor, each of which contains a comparison element connected to a rejecting element, a sealing element for the product containing an outlet tube and a drive for its movement, which is made in the form of a copier with the ability to interact with the output tube.
However, this device does not allow increasing productivity, since this reduces the reliability of testing products.
Figure 1.6 shows an automated device for leak testing based on the chamber method. It consists of a chamber 1, in the cavity of which the controlled product 2 is placed, connected to the air preparation unit 3 through a shut-off valve 4, a membrane separator 5 with a membrane 6 and cavities A and B, a jet element NOR-NOR 7. Cavity A of the membrane separator 5 is connected to the cavity of chamber 1, and cavity B through nozzle 8 is connected to output 9 OR of jet element 7. To its other output 10 NOT OR a pneumatic amplifier 11 with a pneumatic lamp 12 is connected. Cavity B is additionally connected by channel 13 to the control input 14 of jet element 7, atmospheric channels 15 of which are equipped with plugs 16.
The device works as follows. The controlled product 2 is supplied with pressure from the air preparation unit 3, which, when the test level is reached, is cut off by valve 4. At the same time, when power is supplied to the jet element 7, a stream of air through output 9 OR and nozzle 8 passes into cavity B of the membrane separator 5 and through channel 13 - to the control input 14 of the jet element 7. Thus, in the absence of leakage from the controlled product 2, the jet element 7 is in a stable state under the influence of its own output jet. If there is a leak from product 2, pressure increases in the internal cavity of chamber 1. Under the influence of this pressure, the membrane 6 bends and blocks the nozzle 8. The pressure of the air stream at the outlet 9 of the jet element 7 increases. At the same time, the jet disappears at control input 14, and since the jet element OR - NOT OR is a monostable element, it switches to its stable state when the jet exits through output 10 NOT OR. In this case, the amplifier 11 is triggered and the pneumatic lamp 12 signals that the product 2 is leaking. The same signal can be sent to the jet sorting control system.
This device is built on elements of jet pneumatic automation, which increases its sensitivity. Another advantage of the device is its simplicity of design and ease of setup. The device can be used to monitor the tightness of gas fittings using compression methods at low test pressure, if the membrane separator is used as a sensor connected directly to the product being monitored. In this case, the presence of abnormal leakage can be monitored by opening the membrane and nozzle.
Figure 1.6? Leak test device
Figure 1.8 shows a device that provides automation of control of the tightness of pneumatic equipment, for example, electric pneumatic valves, that is, products similar to the gas fittings discussed in the dissertation.
The test product 1 is connected to a pressure source 2, the electromagnetic bypass valve 3 is installed between the output 4 of the product 1 and the exhaust line 5. The electromagnetic shut-off valve 6, with its input 7, is connected during the test to the output 4 of the product 1, and the output 8 to the pneumatic input 9 of the converter 10 of the leakage measurement system 11, which is made in the form of a thermal flow meter. System 11 also contains a secondary unit 12 connected to the control input 13 of the converter 10, the pneumatic output 14 of which is connected to the exhaust line 5. The valve control unit 15 contains a multivibrator 16 and a delay and pulse generation unit 17. One output of the multivibrator 16 is connected to the control input 18 of the shut-off valve 6, the other - to the control input 19 of the valve 3 and the block 17, which is connected during the control process to the drive 20 of the test product 1. The calibration line 21 consists of an adjustable throttle 22 and shut-off valve 23. It is connected in parallel to product 1 and is used to configure the device.
Leakage control is carried out as follows. When the valve control unit 15 is turned on, a pulse appears at the output of the multivibrator 16, which opens the valve 3 and the delay and pulse generation unit 17. The same pulse opens the test product 1 after a set delay time by applying an electrical signal from block 17 to drive 20. In this case, the test gas is released through valve 3 into the exhaust line 5. After a time set by multivibrator 16, the pulse is removed from valve 3, closing it, and is supplied to input 18 of shut-off valve 6, opening it. In this case, the gas, the presence of which is caused by a leak from the product 1, enters the leak measurement system 11 and, passing through it, generates an electrical signal in the converter 10, proportional to the gas flow. This signal enters the secondary unit 12 of the leak measurement system, in which it is corrected, and the amount of gas flow through the closed test product 1 is recorded. After the time set by the multivibrator, required for the leak measurement system to reach a stationary mode, the test cycle is repeated.
The disadvantages of this device include the following. The device is intended for monitoring the tightness of gas fittings of only one type, equipped with an electromagnetic drive. Only one product is controlled at a time, that is, the process is low-productivity.
Figure 1.8 shows a diagram of an automated device for monitoring gas leaks using the compression method with a pneumo-acoustic measuring transducer. The device consists of intermediate blocks that provide control of large leaks (more than 1 / min) and a pneumatic-acoustic block for control of small leaks (0.005...1) / min. The pneumo-acoustic block of the converter has two amplification manometric stages, consisting of micromanometers 1, 2 and acoustic-pneumatic elements 3, 4, connected to each other through the distribution element 5. The measurement results are recorded by a secondary device 6 of type EPP-09, connected to the block through distributor 7. The controlled product 8 is connected to the test pressure source through shut-off valve K4. The device operates in a continuous-discrete automatic mode, which is ensured by a logical control unit 9 and valves -. The controlled product 8, using block 9, is connected in series to the blocks and, correspondingly turning on the valves and, where the preliminary value of the test gas leak is determined. In the case of a small leakage value (less than 1/min), the product is connected via a valve to a pneumatic-acoustic unit, where the leakage value is finally determined, which is recorded by a secondary device 6. The device provides control of gas leaks with an error of no more than ±1.5%. Supply pressure and element tube - tube in the block is 1800 Pa.
This device can be used for automatic control of gas fittings with a wide range of permissible gas leaks. The disadvantages of the device are the complexity of the design due to the large number of measuring units, as well as the simultaneous monitoring of only one product, which significantly reduces the productivity of the process.
Figure 1.8 Automated device for monitoring gas leaks using the compression method.
Devices that provide simultaneous testing of several products are promising for monitoring the tightness of gas fittings. An example of such devices is an automatic machine for monitoring the tightness of hollow products, shown in Figure 1.14. It contains a frame 1, mounted on racks 2 and covered with a casing 3, as well as a rotary table 4 with a drive 5. The rotary table is equipped with a faceplate 6, on which eight slots 7 for products 8 are evenly spaced. The slots 7 are removable and have cutouts 9. Sealing the nodes 10 are fixed on the frame 1 with a step twice the size of the sockets 7 on the faceplate 6. Each sealing unit 10 contains a pneumatic cylinder 11 for moving the product 8 from the socket 7 to the sealing unit and back, on the rod 12 of which a bracket 13 with a sealing gasket 14 is installed In addition, the sealing unit 10 contains a head 15 with a sealing element 16, which communicates through pneumatic channels with an air preparation unit 17 and with a leakage sensor 18, which is a membrane pressure sensor with electrical contacts. The rejection mechanism 19 is installed on the frame 1 and consists of a rotary lever 20 and a pneumatic cylinder 21, the rod of which is pivotally connected to the lever 20. Good and rejected products are collected in appropriate bins. The machine has a control system; current information about its operation is displayed on display 22.
The machine works as follows. The controlled product 8 is installed at the loading position in slot 7 on the faceplate 6 turntable 4. Drive 5 performs a stepwise rotation of the table by 1/8 of a full revolution at certain time intervals. To control the tightness by triggering the pneumatic cylinder 11 of one of the sealing units 10, the product 8 is raised in the bracket 13 and pressed against the sealing element 16 of the head 15. After this, test pressure is supplied from the pneumatic system, which is then cut off. The pressure drop in product 8 is recorded by leakage sensor 18 after a certain monitoring time, which is set by the step of table 4. Stopping table 4 serves as a signal allowing the corresponding operation to be carried out in positions I - VIII while the table is standing. Thus, when the table is rotated one step, one of the following operations is carried out at each of its positions: loading the product; lifting the product to the sealing unit; tightness control; lowering the product into the slot on the faceplate; unloading of suitable products; removal of defective products. The latter arrive at position VIII, while the lever 20, under the action of the pneumatic cylinder rod 21, rotates in the hinge, and with its lower end passes through the cutout 9 of the socket 7, removing the product 8, which falls into the hopper under its own weight. Useful products are unloaded in the same way at position VII (the unloading device is not shown).
The disadvantages of the device are: the need to lift the product from the faceplate into the sealing unit to control the tightness; using a membrane pressure transducer with electrical contacts as a leak sensor, which has low accuracy characteristics compared to other types of pressure sensors.
The conducted studies have shown that one of the promising ways to improve the manometric method of tightness monitoring is the combined use of bridge measuring circuits and various differential-type converters.
The pneumatic bridge measuring circuit for leakage monitoring devices is based on two pressure dividers (Fig. 1.9).
Fig.1.9
The first pressure divider consists of a constant throttle fli and an adjustable throttle D2. The second one consists of a constant throttle D3 and a control object, which can also be considered a throttle D4. One diagonal of the bridge is connected to the source of test pressure pk and the atmosphere, the second diagonal is the measuring diagonal, the PD converter is connected to it. To select the parameters of the elements and configure the bridge circuit, consisting of laminar, turbulent and mixed chokes, the following relationship is used:
where R1 R2, R3, R4 are the hydraulic resistances of elements D1, D2, D3, D4, respectively.
Taking into account this dependence, the possibility of using both balanced and unbalanced bridge circuits, and also the fact that the hydraulic resistance of the supply channels is small compared to the resistance of the chokes and therefore can be neglected, then based on the above pneumatic bridge circuit it is possible to build devices for monitoring the tightness of various objects. At the same time, the control process is easily automated. The sensitivity of the device can be increased by using unloaded bridge circuits, i.e. install transducers with R = in the measuring diagonal. Using formulas for gas flow in subcritical mode, we obtain dependencies for determining the pressure in the inter-throttle chambers of an unloaded bridge.
For the first (upper) branch of the bridge:
for the second (lower) branch of the bridge:
where S1, S2, S3, S4 are the cross-sectional areas of the channel of the corresponding throttle; Pv, Pn - pressure in the interthrottle chamber of the upper and lower branches of the bridge, pk - test pressure.
Dividing (2) by (3) we get
From dependence (4) follows a number of advantages of using a bridge circuit in devices for monitoring tightness using the manometric method: the pressure ratio in the interthrottle chambers does not depend on the test...
Let's consider the schematic diagrams of devices that provide tightness control using the manometric method, which can be built on the basis of pneumatic bridges and various types of differential pressure-to-electric converters and other types of output signals.
In Fig. Figure 1.10 shows a diagram of a control device in which a water differential pressure gauge is used in the measuring diagonal of the bridge.
Figure 1.10 Diagram of a control device with a bridge measuring diagonal - water differential pressure gauge
Test pressure pk is supplied to two lines through constant throttles. One line - the right one is measuring, the pressure in it changes depending on the amount of leakage in the controlled object 4. The second line - the left one provides reference back pressure, the value of which is set by an adjustable throttle 2. Typical devices can be used as this element: cone - cone, cone - cylinder, etc. Both lines are connected to a differential pressure gauge 5, in which the difference in heights of liquid columns h is a measure of the pressure drop p in the lines and at the same time allows one to judge the amount of leakage, because is proportional to it:
The process of reading water differential pressure gauge readings can be automated by using photoelectric sensors, fiber-optic converters, and optoelectronic sensors. In this case, the water column can be used as a cylindrical lens that focuses the light flux, and in the absence of water, dissipate it. In addition, to make readings easier, the water can be tinted and serve as an obstacle to the light flux.
This device provides high-precision leak measurement and can therefore be used for calibration of other instrumentation devices and certification of test leaks.
In Fig. Figure 1.11 shows a device for measuring leakage in object 4, in which a jet proportional amplifier 5 is used in the measuring diagonal of the bridge. Test pressure pk through constant chokes 1 and 3 is supplied to the backpressure line and the measuring line connected to the corresponding control inputs of the amplifier. Under the influence of the pressure of the jet leaving the amplifier, arrow 6, loaded with spring 7, is deflected. The deflection of the arrow corresponds to the amount of leakage. The counting is carried out on a graduated scale 8. The device may be equipped with a pair of closing electrical contacts that are triggered when a leakage exceeds the permissible limit. The use of a jet proportional amplifier makes it easier to adjust the device to a given leakage level and increases the control accuracy.
Figure 1.11 Circuit diagram of a control device with a jet proportional amplifier
However, given that the amplifier has a hydraulic resistance Ry0, the bridge circuit is loaded, which reduces its sensitivity. In this case, as an adjustable tuning throttle 2, it is advisable to use a bubble tank 9 filled with water and a tube 10, one end of which is connected to the throttle 1, forming a backpressure line with it, and the second end has an outlet to the atmosphere and is immersed in the tank. Regardless of the value of the test pressure pk in tube 10, pressure pp will be established, which is determined by the relationship:
where h is the height of the column of water displaced from the tube.
Thus, the adjustment of the back pressure in the bridge circuit is carried out by setting the appropriate h and the immersion depth of the tube. This adjustable throttle device ensures high precision in setting and maintaining back pressure. In addition, it is practically cost-free. However, control chokes of this type can be used in circuits operating at low pressure (up to 5-10 kPa) and mainly in laboratory conditions.
The use of bridge circuits with pneumoelectric membrane converters in leakage monitoring devices ensures their operation in a wide range of pressures pk with sufficient accuracy. The diagram of such a control device is shown in Fig. 1.12.
It consists of constant chokes 1 and 3, as well as an adjustable throttle 2. A membrane transducer 5 is connected to the measuring diagonal of the bridge, with one of its chambers connected to the measuring line of the bridge, and the second to the backpressure line. At the beginning of the process of monitoring the tightness of object 4, membrane b is in the rest position, balanced by the pressures in the inter-throttle chambers of the bridge, which is fixed by closing the right pair of electrical contacts 7. If the object is leaking, i.e. when a leak appears, a pressure difference will arise in the chambers of the converter, the membrane will bend and contacts 7 will open. If a leak appears more than permissible, the amount of membrane deflection will ensure the closure of the left pair of electrical contacts 8, which will correspond to a defective product.
Figure 1.12 Diagram of a control device with a pneumatic membrane converter
The relationship between the membrane stroke and the pressure difference in the chambers in the absence of a rigid center and a small deflection is established by the relationship:
where r is the radius of the membrane, E is the elastic modulus of the membrane material,
Membrane thickness
Taking into account the dependence and leakage Y according to the formula, the dependence can be chosen structural elements and operating parameters of this converter.
In addition to electrical contacts, transducers with flat membranes can be used in conjunction with inductive, capacitive, piezoelectric, magnetoelastic, pneumatic, strain gauge and other output transducers of small displacements, which is their great advantage. In addition, the advantages of pressure transducers with flat membranes are structural simplicity and high dynamic properties.
In Fig. Figure 1.13 shows a diagram of a device designed to control tightness at low and medium test pressures.
Figure 1.13 Diagram of a control device with a two-input three-membrane amplifier
Here, in a pneumatic bridge consisting of constant throttles 1 and 3, an adjustable throttle 2, a comparison element 5 is used in the measuring diagonal, made on a two-input three-membrane amplifier USEPPA type P2ES.1, the blind chamber A of which is connected to the backpressure line, and the blind chamber B is connected with measuring line. The output of the comparison element is connected to an indicator or pneumatic-electric converter 6. The comparison element is powered separately from the bridge and at a higher pressure. Using an adjustable throttle 2, the pressure difference between the measuring line and the backpressure line is set proportional to the maximum permissible leakage. If, during monitoring, the amount of leakage through object 4 is less than permissible, then the pressure pi in the measuring line will be higher than the back pressure pm, and there will be no signal at the output of the comparison element. If the leakage value exceeds the permissible value, then the pressure in the measuring line will become less than the back pressure, which will lead to the switching of the comparison element and high pressure will appear at its output, this will force the indicator or pneumoelectric converter to operate. The operation of this scheme can be described by the following inequalities. For control objects with an acceptable leakage value:
For control objects with leakage exceeding permissible:
This device can be used in automated stands for monitoring the tightness of shut-off valves. An additional advantage is the ease of implementation of the design using standard pneumatic automation elements.
In Fig. Figure 1.14 shows a device for measuring and monitoring leakage in object 4, in which a differential bellows converter 5 is connected to the measuring diagonal of the bridge. Test pressure p is supplied through constant throttle 1 to bellows 6 of the backpressure line, and through constant throttle 3 to bellows 7 of the measuring line. The pressure value corresponding to the permissible leakage is set by adjustable throttle 2.
Bellows 6 and 7 are connected to each other by a frame on which an indication system is mounted, consisting of an arrow 8 with a scale 9 and a pair of adjustable closing electrical contacts 10. The device is configured in accordance with the dependence:
Figure 1.14 Diagram of a control device with a differential membrane converter
If a leak occurs, the pressure p in bellows 7 begins to decrease, and it contracts, and bellows 6 will stretch, because rp remains constant, the frame will begin to move and the arrow will show the amount of leakage. If the leak exceeds the permissible limit, then the corresponding movement of the bellows will close the electrical contacts 10, which will give a signal about the defect of the test object.
This device can operate at medium and high test pressure. It can be used in automated stands for monitoring the tightness of high-pressure shut-off valves, where relatively high leakage values are allowed and measurement of their absolute values is required.
- 1. The use of pneumatic bridge circuits in conjunction with various types of differential converters significantly expands the possibilities of using the manometric method for automating leak testing.
- 2. Automated devices for tightness monitoring based on bridge circuits can be implemented using standard logic elements, as well as serial differential sensors used to monitor various technological quantities, which significantly speeds up their creation and reduces cost.
Introduction
Chapter 1 Analysis of the state of the problem of automation of tightness control and formulation of the research problem 9
1.1 Key terms and definitions used in this study 9
1.2 Features of gas valve tightness control 11
1.3 Classification of gas testing methods and analysis of the possibility of their use for monitoring the tightness of gas fittings 15
1.4 Review and analysis of automatic leak testing using the manometric method 24
1.4.1 Primary transducers and sensors for automatic leak control systems 24
1.4.2 Automated leak control systems and devices 30
Purpose and objectives of the study 39
Chapter 2 Theoretical study of the manometric leak test method 40
2.1 Determination of gas flow regimes in test objects... 40
2.2 Study of the compression method of testing for leaks 42
2.2.1 Study of time dependencies when monitoring tightness using the compression method 43
2.2.2 Study of the sensitivity of tightness control using the compression method with a cutoff of 45
2.3 Study of the comparison method with continuous supply of test pressure 51
2.3.1 Scheme for monitoring tightness using the method of comparison with continuous supply of test pressure 52
2.3.2 Study of time dependencies when monitoring tightness using the comparison method 54
2.3.3 Study of the sensitivity of tightness control by comparison with continuous supply of test pressure 65
2.3.4 Comparative assessment of the sensitivity of tightness control using the compression method with cutoff and the comparison method 68
You water to chapter 2 72
Chapter 3 Experimental study of the parameters of leakage control circuits based on the comparison method 75
3.1 Experimental setup and research methodology 75
3.1.1 Description of the experimental setup 75
3.1.2 Methodology for studying leakage monitoring circuits 78
3.2 Experimental study of the leak control scheme based on the comparison method 81
3.2.1 Determination of the characteristic p = f(t) of the lines of the leakage control circuit 81
3.2.2 Studies of the timing characteristics of the lines of the tightness control circuit using the comparison method 86
3.2.3 Study of the static characteristics of the measuring line of the tightness control circuit 91
3.3. Experimental study of a device for leak testing based on the comparison method 97
3.3.1 Study of a model of a leak testing device with a differential pressure sensor 97
3.3.2 Assessment of the accuracy characteristics of devices for leak testing, performed according to the comparison scheme 100
3.4 Probabilistic assessment of the reliability of sorting products when monitoring tightness using the comparison method 105
3.4.1 Experimental study of the distribution of the pressure value equivalent to the leakage of test gas in a batch of products 105
3.4.2 Statistical processing of the results of the experiment to assess the reliability of sorting 108
4.3 Development of leak sensors with improved performance 126
4.3.1 Design of the leakage sensor 127
4.3.2 Mathematical model and algorithm for calculating the tightness sensor 130
4.4 Development of an automated stand for leak testing.133
4.4.1 Design of an automated multi-position stand 133
4.4.2 Selection of parameters for leakage monitoring circuits 142
4.4.2.1 Method for calculating the parameters of the tightness control circuit using the compression method with cutoff 142
4.4.2.2 Methodology for calculating the parameters of the tightness control circuit using the comparison method 144
4.4.3 Determining the performance of an automated test stand for leak testing 146
4.4.4 Determination of parameters of sealing seals for an automated stand 149
4.4.4.1 Calculation method for a sealing device with a cylindrical collar 149
4.4.4.2 Method for calculating the mechanical ring seal 154
General conclusions and results 157
References 159
Appendix 168
Introduction to the work
An important issue in a number of industries there is an increase in requirements for the quality and reliability of products. This creates an urgent need to improve existing ones, create and implement new methods and means of control, including tightness control, which relates to flaw detection - one of the types of quality control of systems and products.
IN industrial production shut-off and distribution valves, in which the working medium is compressed air or other gas, existing standards and technical conditions for its acceptance usually regulate one hundred percent control of the “tightness” parameter. The main unit (working element) of such valves is a movable “plunger-body” pair or a rotary valve element, which operate over a wide pressure range. To seal gas fittings, various sealing elements and lubricants (sealants) are used. During the operation of a number of gas fitting designs, a certain leakage is allowed working environment. Exceeding the permissible leakage due to poor-quality gas fittings can lead to incorrect (false) operation production equipment on which it is installed, which may cause a serious accident. Increased leakage in household gas stoves natural gas may cause a fire or poisoning of people. Therefore, exceeding the permissible leakage of the indicator medium with appropriate acceptance control of gas fittings is considered a leak, i.e., a defective product, and eliminating defects increases the reliability, safety and environmental cleanliness of the entire unit, device or device in which the gas fittings are used.
Monitoring the tightness of gas fittings is a labor-intensive, time-consuming and complex process. For example, in the production of pneumatic mini-equipment it takes up 25-30% of the total labor intensity and up to 100-120% of the time
assemblies. This problem can be solved in large-scale and mass production of gas fittings by using automated methods and control tools, which should ensure the required accuracy and productivity. In real production conditions, solving this problem is often complicated by the use of control methods that provide the necessary accuracy, but are difficult to automate due to the complexity of the method or the specifics of the test equipment.
About ten methods have been developed for testing the tightness of products using only a gaseous test medium, for the implementation of which more than a hundred have been created in various ways and controls. Development modern theory and the practice of tightness control are devoted to the studies of Zazhigin A. S., Zapunny A. I., Lanis V. A., Levina L. E., Lembersky V. B., Rogal V. F., Sazhina S. G., Tru-shchenko A. A., Fadeeva M. A., Feldmana L. S.
However, there are a number of problems and limitations in the development and implementation of leak control means. Thus, most high-precision methods can and should be applied only to large-sized products in which complete tightness is ensured. In addition, restrictions of an economic, design nature, environmental factors, and safety requirements for operating personnel are imposed. In serial and large-scale production, for example, of pneumatic automation equipment, gas fittings for household appliances, in which a certain leakage of the indicator medium is allowed during acceptance tests and, therefore, the requirements for control accuracy are reduced, the possibility of its automation and, on this basis, ensuring high productivity of the corresponding control and sorting equipment, which is necessary for 100% product quality control.
An analysis of the equipment features and the main characteristics of the gas leak testing methods most used in industry allowed us to conclude that they are promising for automation of leak testing.
the accuracy of gas fittings using the comparison method and the compression method, implementing the manometric method. In the scientific and technical literature, little attention has been paid to these testing methods due to their relatively low sensitivity, but it is noted that they are most easily automated. At the same time, there are no recommendations for the selection and calculation of parameters of leakage monitoring devices performed according to a comparison scheme with a continuous supply of test pressure. Therefore, research in the field of gas dynamics of blind and flow-through tanks, as elements of control circuits, as well as techniques for measuring gas pressure as a basis for creating new types of converters, sensors, devices and systems for automatic control of the tightness of products, promising for use in gas production, is relevant and important. fittings.
When developing and implementing automated leakage monitoring devices, an important question arises about the reliability of the control and sorting operation. In this regard, the dissertation carried out a corresponding study, on the basis of which recommendations were developed that make it possible, during automatic sorting according to the “tightness” parameter, to exclude defective products from entering suitable ones. One more important issue is to ensure the specified performance of automated equipment. The dissertation provides recommendations for calculating the operating parameters of an automated stand for leak testing depending on the required performance.
The work consists of an introduction, four chapters, general conclusions, a list of references and an appendix.
The first chapter discusses the features of monitoring the tightness of gas fittings, which allow a certain leakage during operation. A review of gas leak testing methods, classification and analysis of the possibility of their use for automating the control of gas fittings is given, which made it possible to select the most promising - the manometric method. Devices and systems that provide automation of tightness control are considered. The goals and objectives of the study are formulated.
The second chapter theoretically examines two methods of tightness control that implement the manometric method: compression with pressure cut-off and a comparison method with continuous supply of test pressure. Mathematical models of the methods under study were determined, on the basis of which studies of their time characteristics and sensitivity were carried out under different gas flow regimes, different line capacities and pressure ratios, which made it possible to identify the advantages of the comparison method. Recommendations are given for the selection of parameters for tightness control circuits.
In the third chapter, the static and temporal characteristics of the lines of the tightness control circuit are experimentally studied using the method of comparison with different meanings leakage, line capacity and test pressure, their convergence with similar theoretical dependencies is shown. The performance of the device for leak testing, made according to the comparison scheme, was experimentally tested and the accuracy characteristics of the device were assessed. The results of assessing the reliability of sorting products according to the “tightness” parameter and recommendations for setting up the corresponding automated control and sorting devices are presented.
The fourth chapter provides a description of typical automation schemes for the manometric test method and recommendations for the design of automated equipment for leak testing. The original designs of a leakage sensor and an automated multi-position stand for leakage control are presented. Methods for calculating leakage control devices and their elements, presented in the form of algorithms, are proposed, as well as recommendations for calculating the operating parameters of a control and sorting stand depending on the required performance.
The Appendix presents the characteristics of gas leak testing methods and time dependencies for possible sequences of changes in gas flow regimes in a flow-through container.
Features of gas valve tightness control
The developments and research presented in the dissertation are related to gas fittings, in the manufacture of which existing standards and technical conditions regulate 100% control of the “tightness” parameter and a certain leakage of the working medium is allowed. The gas fittings considered in this work are understood as devices intended for use in various systems, in which the working medium is gas or a mixture of gases under pressure (for example, natural gas, air, etc.), to perform the functions of cut-off, distribution, etc. Gas fittings include: valves, distributors, valves and other means of industrial pneumatic automation high (up to 1.0 MPa) and medium pressure (up to 0.2...0.25 MPa), shut-off valves for household gas stoves operating at low pressure (up to 3000 Pa). Both finished products and their components, individual components, etc. are subjected to leak testing. Depending on the purpose of the products, the conditions in which they are operated and the design features, they are subject to different requirements regarding their tightness.
The tightness of gas fittings is understood as its ability not to allow the working medium supplied under excess pressure to pass through the walls, connections and seals. In this case, a certain amount of leakage is allowed, the excess of which corresponds to the leakage of the product. The presence of a leak is explained by the fact that the main unit - the working element of such devices is a moving, difficult to seal pair: spool-housing, nozzle-flap, ball, cone or seat valves, etc. In addition, the design of the device, as a rule, contains fixed sealing elements: rings, cuffs, seals, lubricants, defects of which can also cause leakage. Leakage of gas fittings, i.e. the presence of leakage of the working medium exceeding the permissible limit, can lead to serious accidents, breakdowns and other negative results in the operation of the equipment in which it is used. The shut-off valve (Fig. 1.1) is an important component of household gas stoves. It is designed to regulate the supply of natural gas to the burners of the stove and cut it off at the end of work. Structurally, the faucet is a device with a rotary valve element 1 mounted in a split housing 2, which has channels for the passage of gas. The interface between the faucet parts needs to be sealed to ensure maximum possible tightness. The seal is carried out with a special graphite lubricant - sealant, manufactured in accordance with TU 301-04-003-9. Poor-quality sealing leads to a leak of natural gas during operation of the stove, which, in conditions of limited space in domestic premises, is an explosion and fire hazard; in addition, the ecology (human environment) is disturbed.
In accordance with the following requirements are established when testing the tightness of a shut-off valve. Tests are carried out with compressed air under pressure (15000±20) Pa, since higher pressure may damage the sealing lubricant. Air leakage should not exceed 70 cm3/h. The permissible volume of switching channels and containers of the control device is no more than (1 ±0.1) dm3. Control time 120 s.
It is recommended to monitor the leakage of compressed air in laboratory conditions using a volumetric device (Fig. 1.2). The device consists of a measuring burette 1, to which air under pressure is supplied through channel 2, a reserve vessel 3, a vessel 4 to maintain the required level and a connection point for the test tap 5. It is possible to carry out control using other devices, the safety of which does not exceed the safety of the volumetric device ± 10 cm3/h. Leakage control is carried out by measuring the displaced volume of water.
Medium and high pressure gas fittings that need to be tested for leaks include pneumatic distributors, switches, adjustable throttles and other pneumatic equipment, typical designs of which are shown in Fig. 1.3 and 1.4. In Fig. 1.3 shows a pneumatic distributor with a cylindrical spool type P-ROZP1-S, a crane pneumatic distributor with a flat spool type B71-33
channel 1 for the control signal, cylindrical spool 2, housing 3, cover with channel 4 connecting to the atmosphere, working channel 5 and o-ring 6. In Fig. 1.4 shows a crane pneumatic valve with a flat spool type B71-33, consisting of a body 1, a cover 2, a flat rotary spool 3, a handle 4, a roller 5, working channels 6, 7, 8, 9, a channel 10 connecting to the atmosphere and a channel for supply of compressed air 11. The presence of regulated leakage in pneumatic equipment is explained by the fact that its designs contain flat spools, cylindrical spools with a sealing gap, valve and tap devices, which involve leakage of compressed air from one cavity to another or leakage into the atmosphere through gaps and leaks . The amount of permissible leakage of a particular pneumatic device is established by the developer on the basis of GOST and is indicated in its technical characteristics. The permissible leakage values for various types of pneumatic devices at the nominal compressed air pressure set for this device are given in Table 1.1. Pneumatic equipment is used in control systems for various industrial equipment, so increased leakage of the working medium and, as a result, a drop in pressure can lead to the device not operating or cause a false operation, i.e. lead to an emergency situation, equipment breakdown.
When testing the tightness of pneumatic equipment, difficulties arise due to the variety of designs, the wide range of permissible leakage of the indicator medium (0.0001...0.004) m3/min; varying test pressure (0.16...1.0) MPa and control time (tens of seconds or more). In addition, contamination of the indicator medium (compressed air) should not exceed class 1 according to GOST 17433-91, ambient temperature 20±5C. The error of measuring and control instruments used to determine the leakage value should not exceed ±5%. To monitor the tightness of pneumatic equipment, pressure sensors (alarms) and specially designed equipment are used. An analysis of these devices is given in section 1.4.
Study of the sensitivity of tightness control using the compression method with cutoff
Leak control sensitivity is the smallest sample gas leakage that can be measured during product testing. We study the dependence of the sensitivity of compression tightness control Table 2.2 Time dependences for various sequences of modes of gas outflow from a blind chamber Variants of pressure ratio Sequence of changes in outflow modes in the transient process Time dependences using the ion method with a cutoff from the test pressure p0 at given V and pd for various modes of gas outflow through throttle, i.e., with corresponding gas leaks through leaks in the test object. Let us express the gas leakage Y in terms of the mass flow rate G. Assume that, regardless of the gas outflow mode, at the conductivity value f the leakage is equal to U, and at conductivity / the leakage is equal to V. For the turbulent supercritical mode, after substituting formula (2.5) into (2.15), we obtain: With the same test duration /, -(as a result of transformation (2.19) and (2.20), we obtain the relation (2.21) Substituting (2.21) into (2.18), we obtain the relation Since in (2.23) the LU will have the same absolute value regardless of the relations Ud U or Ud U, then to simplify the calculations we assume that Ud U. Then (2.23) can be represented as an expression - the response of pressure pA to a change in leakage AC. If, in dependence (2.25), the value Art is taken equal to the sensitivity threshold pp of the manometric measuring device , then we obtain a formula for determining the smallest change in leakage U, which can be recorded when monitoring tightness using the method under study. In accordance with the definition, this value U is the sensitivity of tightness control using the compression method with cutoff in a turbulent supercritical mode
Transformation (2.25) with respect to p0 allows us to obtain an expression for determining the test pressure depending on the sensitivity of the control unit for tightness control in a turbulent supercritical mode. Substituting dependence (2.35) instead of D/? on the sensitivity threshold pp of a manometric measuring device, we obtain a formula for determining the sensitivity of the control unit for tightness control compression method with cut-off in a turbulent subcritical mode Transformation (2.36) with respect to p0 allows us to obtain an expression for determining the test pressure depending on the sensitivity of the tightness control unit in a turbulent subcritical mode ґ Ґ у лу, With the same test duration /, = / as a result of the transformation ( 2.41) and (2.42) we obtain the relation
Study of a comparison method with a continuous supply of test pressure. The general provisions and design of the leak test using the comparison method with cutoff of the test gas source are discussed in Section 1.3.2. However, as the analysis showed, a method of comparison with a continuous supply of test pressure is promising for further research. This is explained by the fact that shut-off, distribution and switching gas fittings in real conditions operate under constant operating pressure and technical specifications allows a certain amount of leakage. Therefore, to test the tightness of this class of devices, it is advisable to use a control circuit with a continuous supply of test pressure, as it is most appropriate to the actual conditions of their operation. In addition, the need to shut off the pressure source during each test is eliminated, which significantly simplifies the design of the control device and facilitates automation of the testing process. 2.3.1 Scheme of tightness control by comparison method with continuous supply of test pressure A diagram is presented that explains tightness control by comparison method with continuous supply of test pressure. The circuit consists of a measuring line IL and a reference pressure line EL, the inputs of which are connected to a common source of test pressure pQ, and the outputs are connected to the atmosphere. The reference pressure line contains an input pneumatic resistance (throttle) with conductivity /J, a capacitance with an adjustable volume Ge and an output pneumatic resistance with adjustable conductivity /2, which are intended for setting up the circuit. The measuring line contains an input pneumatic resistance with conductivity /t, and a test object OI, which can be represented as a container with a volume Ki, having a leak equivalent to the pneumatic resistance with conductivity f4. The measuring and reference lines form a pneumatic measuring bridge. Comparison of pressures in the lines of the circuit is carried out using a differential pressure measuring device IU, included in the diagonal of the pneumatic bridge. In this circuit, the measuring device has a conductivity / = 0, so the pressure /g and pH in the lines do not depend on each other. Each line of the diagram represents a flow tank. When checking the tightness according to the scheme shown in Fig. 2.2, leakage is understood as the volumetric flow of gas through all through leaks of the test object at a steady state of test gas flow in the lines of the circuit. This mode corresponds to the same mass flow of gas through the input and output resistance in the line.
Methodology for studying leakage monitoring schemes
The experimental study was carried out using serial industrial samples of shut-off valves for household gas stoves (at low test pressure), shut-off and distribution equipment for pneumatic automation (at medium and high test pressure), as well as leak models. The following methodology was used: 1. Length of the pneumatic line from the outlet of the air preparation unit to the stabilizer w Fig. 3.3 Special equipment for experimental research: a - variable capacity; b - throttle with a diameter of 0.1 mm; c - control leaks: 1 - cylinder; 2 - cover; 3 - piston; 4 - volume clamp; 5 - inlet fitting; 6 - outlet fitting; 7 - collet clamp; 8 - replaceable tube (internal diameter 0.1 mm) pressure at the inlet of the experimental installation was no more than 1.5 m. 2. During testing, stabilization of the test gas (compressed air) from fluctuations in network pressure was ensured. 3. The contamination of the test gas did not exceed the requirements of class 1 according to GOST 17433-80. 4. Setting the value of the test pressure supplied to the model circuits and leakage control devices was carried out with the adjusting screw of the pressure stabilizer of the experimental installation. 5. The measurement of the test pressure at the inlet of the circuit models and the tightness control device was carried out with standard pressure gauges of class 0.4 with measurement limits of 0... 1; 0... 1.6; 0...4 kgf/cm. 6. Measurement of pressure in the reference and measuring lines of the circuit models and leakage monitoring device was carried out with standard pressure gauges of class 0.4 with measurement limits of 0...1; 0...1.6; 0...4 kgf/cm and a liquid micromanometer with a relative measurement error of 2%. 7. In studies at medium (up to 1.5 kgf/cm "0.15 MPa) and high test pressure (up to 4.0 kgf/cm "0.4 MPa), the required leakage was set using adjustable chokes, previously calibrated using a rotameter with a relative measurement error of 2.5%. 8. In studies at low test pressure (up to 0.3 kgf/cm "ZOkPa), the required leakage was set using control leaks made in the form of metal slotted capillaries made of L63 brass (Fig. 3.3, c). The capillaries were obtained by drilling holes with a diameter of 1 mm and subsequent flattening of the end section with a length of "20 mm. Calibration of control leaks was carried out with air at a pressure of 15 kPa using a volumetric device with a relative error of 2%. 9. Setting the pneumatic capacity of the reference and measuring lines of the tightness control circuits was carried out using a set of permanent containers, and installation of equal capacities in lines - through variable (adjustable) capacities. 10. The measurement of the pressure difference between the lines in the control device model was carried out by a differential pressure gauge with a relative measurement error of 2% and measurement limits of 0...25 kPa and 0...40 kPa. 11. When taking time characteristics, time was counted using an electronic stopwatch with a relative measurement error of 0.5%. 12. Measurements of the corresponding parameters (pi, Ap, I) for each studied characteristic or parameter of the model of the circuit or leakage control device were carried out by repeating the readings at least 5 times. 13. The results of each experiment were processed by finding the average parameter values for each experiment. Based on the data obtained, the corresponding characteristics were constructed. Descriptions of the methodology for studying individual characteristics are given in the relevant sections of this chapter. Study of the characteristics p = /(/) of the lines of the tightness control circuit To check the adopted mathematical model (2.48) and the operability of the tightness control circuit, performed on the basis of a comparison method with a continuous supply of test pressure, an experiment was carried out to determine the characteristic p = f(J) - change pressure in its lines during monitoring at high and low test pressure, which are used when monitoring tightness in various gas fittings. In section 2.3.1 it was shown that this scheme control contains two lines, each of which can be represented as a flow tank. The study used the experimental setup shown in Fig. 3.2, as well as the recommendations of Chapter 2, that all parameters of the measuring and reference lines of the circuit must be equal, so the experiment was carried out only with the measuring line. For this purpose, valves 15 connecting the reference line to the source of test pressure and the measuring line to the differential pressure gauge device 14 were closed.
To determine the characteristics p = /(/) of the flow capacity of the line at high test pressure, a standard pressure gauge 8 with an upper measurement limit of 4.0 kgf/cm (400 kPa) class 0.4 and an electronic stopwatch were used. The following parameters were set in the experiment: test pressure/?о=400 kPa; air leakage value Y = 1.16-10-5 m3/s; the total volume of the flow tank and pneumatic channels V “0.5 dm3. The amount of air leakage Y was determined by variable throttle 10 of type P2D.1M calibrated against the rotameter, while the control leak 9 was closed by valve 15. In the interval of intense pressure increase, readings of pressure gauge 8 were taken after 10 s. To construct the experimental characteristic p = /(/), the arithmetic mean values from five experiments were taken as the pressure change values.
Recommendations for the design of automated equipment...
Let's consider the main stages of technical design of automated equipment for leak testing. At the first stage, a technological analysis of the nomenclature and volume of the product batch is carried out. It should be taken into account that the number of products in a batch should be large enough (if possible, correspond to medium-scale and large-scale production) to ensure the necessary load of the designed control equipment without reconfiguring it. If the production is multi-product and the batch size is small, then it is recommended to combine products of different production batches and types into groups according to general technical conditions for leakage control, which allows the use of a single control scheme and instrumentation, as well as grouping according to similar designs of product bodies and their input channels, which allows the use of common sealing elements, loading and fixing devices when designing. Here it is also necessary to analyze the suitability of product designs and technical requirements for their leak testing to automate this operation. Rational grouping of products allows you to design equipment with maximum productivity and minimal changeover for the control of various types of products. For example, high-pressure pneumatic automation equipment can be grouped according to the same specifications for controlling compressed air leakage (based on the test pressure of 0.63 MPa and 1.0 MPa, as well as the same permissible leakage), according to a similar design of the pneumatic input channel, which makes it possible to use it in the equipment being developed in the first case there is a common control block, and in the second case there is an identical sealing device (end or internal lip). This stage ends with determining the performance of the designed equipment, an example of calculation of which is discussed in section
At the second stage of design, the need to re-adjust the designed device is determined, which should provide for: the ability of the control system to function taking into account different test times from parts under pressure; reconfiguring the control and measuring unit to different permissible values of test gas leakage, as well as to different levels of test pressure. Then you should select the control method and means of its implementation. Preliminary technical conditions for conducting leak testing should be considered when analyzing the technical specifications. Here, as a rule, preference should be given to standard, wide-range control and measuring devices. But in some cases, it is recommended to develop a special control unit that fully meets the requirements of the designed automatic or semi-automatic device, for example, the requirement for device adaptability, test pressure range. Examples of calculation and application of control equipment are discussed in sections 4.3 and 4.4.
At the third design stage, the level of automation and reconfigurability of the entire device is selected. Leak testing machines include devices that carry out the entire process of leak testing, including sorting, as well as loading and unloading of products without operator participation. Automated devices (semi-automatic) for leak testing include devices in which an operator participates. It can carry out, for example, loading and unloading of the test product, sorting for “Good” and “Reject” according to information from a control and measuring unit equipped with an automatic recording element. In this case, the general control of the device, including the drive of the transport device, clamping and releasing (fixing), compaction of the product, control time delay and other functions are carried out automatically. Prospective schemes for automating tightness monitoring using the manometric method are discussed in section 4.2.
After assessing the level of automation, the next important task is the selection and analysis of the layout diagram, which should be drawn to scale. It allows you to rationally arrange all devices of the designed equipment. Here Special attention attention should be paid to the choice of loading position - unloading of the product, the trajectory of movement of the loading equipment. The problems are related to the fact that the loaded products (test objects), as a rule, have a complex spatial configuration, and therefore are difficult to navigate, grasp and hold. Because of this, it is necessary to create special orienting and loading and unloading equipment, which is not always acceptable. economic reasons, so manual loading may turn out to be rational decision. As an adequate solution to the issue, it is recommended to consider the use of industrial manipulators and robots. Examples of selection and calculation of parameters of some auxiliary equipment are given in section
Next important stage design is the choice of control system and synthesis of control circuits. Here you should adhere to recommendations and methods for developing control systems technological equipment given in the literature. The choice of air preparation scheme is quite simple, as it is well technically worked out and covered in the literature. But underestimating the importance of this issue can lead to increased contamination of the compressed air (with mechanical impurities, water or oil) used as a test gas, which will seriously affect the accuracy of control and the reliability of the equipment as a whole. The requirements for air used in pneumatic control and measuring devices are set out in GOST 11662-80 “Air for supplying pneumatic instruments and automation equipment1”. In this case, the pollution class must be no lower than the second according to GOST 17433-80.
When choosing a test pressure supply circuit, one should take into account its mandatory stabilization with high accuracy, the need to connect to a rotary clock table or other moving equipment, as well as the simultaneous power supply of a large number of control units. These issues are discussed using the example of an automated test stand for leak testing in section 4.4.
At the final stage it is carried out expert review project of an automated device for leakage control. Here it is advisable to evaluate the project collectively, according to certain criteria, with the involvement of specialists from the department where the implementation of the device being developed is planned. Then an economic assessment of the project is carried out. Based on the conclusions made, final decisions are made on the further development of working documentation, the creation and implementation of an automatic or automated device for monitoring tightness for this project.
Kavalerov, Boris Vladimirovich
NEWS OF VolgSTU 65 UDC 620.165.29 G. P. Barabanov, V. G. Barabanov, I. I. Lupushor AUTOMATION OF TIGHTNESS CONTROL OF GAS PIPELINE FITTINGS Volgograd State Technical University E-mail: [email protected] Methods for automating the tightness control of gas pipeline shut-off and switching valves are considered. Constructive diagrams of devices are presented that make it possible to implement in practice methods for automating the tightness control of various gas fittings. Key words: tightness control, gas fittings, test pressure. Automation methods of hermeticity control of gas pipelining laking and shifting fittings are considered. Structural schemes of devices, that allow to realize on practice hermeticity control of different gas fittings automation methods are given. Keywords: hermeticity control, gas fittings, test pressure. When manufacturing gas pipeline fittings for industrial and household appliances, the final stage of its production is monitoring the “tightness” parameter, which consists of detecting unacceptable gas leaks during operation of these devices. Gas pipeline fittings include valves, taps, taps for gas stoves, etc. Elimination of gas leaks during operation pipeline fittings increases the reliability, efficiency, safety and environmental friendliness of both industrial and household gas appliances. However, monitoring the tightness of pipeline fittings low pressure due to a number of problems associated with both the labor intensity of the control process and design features these products. So, when checking the tightness of taps on a household gas stove, the test pressure is limited to 0.015 MPa. This control condition is explained by the fact that at a higher test pressure the viscous graphite seal separating the working cavities of the valve is destroyed. Tightness testing by known means at such a low test pressure does not guarantee the required accuracy and performance. Solving these problems in the context of large-scale production of gas pipeline fittings is possible by choosing a rational method for monitoring tightness and automating the monitoring process. An analysis of the features of tightness control of low-pressure pipeline fittings, for example, for household gas appliances, from the point of view of accuracy and the possibility of automating tests, made it possible to identify two promising schemes that implement the manometric control method. This method consists in creating a test pressure value in the cavity of the controlled product, determined by the control requirements, with subsequent comparison of the pressure value at the beginning and at the end of the tests. An indicator of product leakage is a change in test pressure by a certain amount during the period of time established by the control conditions. As studies have shown, this method is advisable to use when monitoring the tightness of products with working volumes of no more than 0.5 liters, since with an increase in the volume of the test chamber, the inspection time increases significantly. One of the schematic diagrams of a leak monitoring device based on a drop in test pressure is shown in Fig. 1. Air from the pressure source through filter 1 and stabilizer 2, through which the required input pressure of 0.14 MPa is set using pressure gauge 3, is supplied to the inlet fitting of the pneumatic toggle switch 4. From the output of the pneumatic toggle switch 4, air simultaneously enters the measuring line of the device and the membrane chamber 15 clamping device 11. The measuring line of the device is built on the principle of a balanced bridge with a reference and measuring circuits. The reference circuit consists of a series-connected unregulated pneumatic resistance 7 and an adjustable pneumatic resistance 8, which form a throttle divider (shown in dotted lines). The measuring circuit is formed by an unregulated pneumatic resistance 9 and a controlled valve 13. Compressed air enters the reference and measuring circuit 66 NEWS OF VolgSTU at a test pressure of 0.015 MPa, which is set by the set pointer 5. A comparison element 6 is included in the diagonal of the measuring bridge, the output of which is connected to a pneumatic indicator 14. The comparison element 6 is powered by compressed air under a pressure of 0.14 MPa. Using an adjustable pneumatic resistance 8 and a reference circuit, the permissible leakage value is set. Pressure from the throttle divider is supplied to the lower blind chamber of the comparison element 6. The upper blind chamber of this element is connected to the channel between the pneumatic resistance 9 and the controlled valve 13. After installing the controlled valve 13 and clamping it in fixture 11, a pressure proportional to the amount of air leakage will be established in the measuring circuit through controlled tap 13. Fig. 1. Diagram of a leakage monitoring device based on a drop in test pressure. If the leakage value is less than permissible, then the pressure will be higher than the reference one, and there will be no signal at the output of comparison element 6, i.e. The tested tap 13 is considered leak-tight. If the leakage value exceeds the permissible value, the pressure will become less than the reference one, which will lead to the switching of the comparison element 6 and high pressure will appear at its output, which will be signaled by the pneumatic indicator 14. In this case, the test valve 13 is considered leaky. To install and seal the valve 13 in the control device, a clamping device 11 is used, containing a hollow rod 10 fixed to the membrane of the chamber 15, through which test pressure enters the cavity of the controlled valve 13. In this case, the rod 10 is fitted with an elastic rubber bushing 12. After compressed air is supplied to the membrane chamber 15, the rod 10 moves down. In this case, the rubber bushing 12 is compressed and, increasing in diameter, fits tightly to the inner surface of the controlled valve 13, ensuring a reliable seal of the connection during the test. The release of the controlled valve 13 and the preparation of the clamping device 11 for installing the next valve is carried out by switching the pneumatic toggle switch 4. The operation of the circuit of this device can be described by the following equations: for control objects with an allowable amount of test gas leakage, i.e., which are considered sealed t⋅ У pi − ≥ pe V for test objects with test gas leakage exceeding the permissible limit, i.e., which are considered leaky t⋅У pi −< pэ, V где У – суммарная утечка индикаторного газа; t – время контроля; V – контролируемый на герметичность объем в объекте; pи – давление в измерительной цепи; pэ – величина давления в эталонной цепи. 67 На рис. 2 приведена принципиальная схема устройства контроля герметичности изделий, имеющих две смежные полости, между которыми возможна утечка газа. Устройство состоит из системы управления, которая содержит реле времени 1, триггер со счетным входом 2 и коммутирующую кнопку 3. При этом реле времени 1 подключено к электромагнитным приводам вентилей. 4 и 5, инверсный выход триггера 2 – к приводам клапанов 6 и 7, каналы которых соединены с датчиками давления 8 и 9, а также с полостями П1 и П2 контролируемого изделия 11. Выходы датчиков 8 и 9 подключены к отсчетному блоку 10. Устройство работает следующим образом. После выдачи входного сигнала кнопкой 3 на реле времени 1 открываются вентили 4 и 5. Этим обеспечивается подключение полости контролируемого изделия 11 через нормально открытый канал клапана 6 к источнику вакуума и полости П2 через нормально открытый канал клапана 7 – к источнику избыточного давления газа. Рис. 2. Схема с изменением направления перепада давления в контролируемом изделии После того, как в полости П1 создастся заданный требованиями контроля уровень вакуума (0,015 МПа), а в полости П2 – заданный уровень избыточного давления (0,015 МПа), происходит срабатывание реле времени 1 и отключаются вентили 4 и 5. С этого момента начинается процесс контроля герметичности изделия 11. Результат контроля определяется по показаниям отсчетного блока 10, сравнивающего сигналы от датчика 8, контролирующего повышение давления в полости П1, и датчика 9, контролирующего понижение давления в полости П2. В случае обнаружения негерметичности испытание прекращается и изделие бракуется. Если датчики 8 и 9 не регистрируют на- рушение герметичности изделия 11, то осуществляется второй этап испытания. Выдается повторный входной сигнал на реле времени 1 и триггер 2. При этом сигнал управления появится на инверсном выходе триггера 2 и переключит клапаны 6 и 7, а реле времени 1 повторно включит вентили 4 и 5. Полость П1 контролируемого изделия 11 окажется подсоединенной к источнику избыточного давления газа, а полость П2 – к источнику вакуума. На этом этапе испытаний в полости П1 контролируется понижение давления, а в полости П2 – повышение давления газа. Если датчики 8 и 9 не зарегистрируют негерметичность изделия 11 и на втором этапе испытаний, то оно считается годным. 68 ИЗВЕСТИЯ ВолгГТУ Особенностью реализуемого в устройстве (рис. 2) способа контроля герметичности является создание двукратного изменения направления перепада давления в контролируемом изделии, т. е. проведение испытаний в два этапа для учета various conditions gas flow in different directions through microdefects in the sealing element of the controlled product, if any. In addition, the creation of a vacuum in one cavity and excess pressure in an adjacent cavity does not exceed absolute value permissible pressure on the sealing element, but at the same time creates twice the pressure drop in places of possible gas leakage. This makes it possible to increase the reliability and accuracy of gas valve tightness monitoring and reduce its duration. The circuits and principles of operation of the devices considered allow automation of the process of monitoring the tightness of gas fittings, which will significantly increase test productivity and virtually eliminate the production of leaky products. BIBLIOGRAPHICAL LIST 1. GOST 18460–91. Household gas stoves. General technical conditions. – M., 1991. – 29 p. 2. Barabanov, V. G. On the issue of studying the manometric method of testing for tightness / V. G. Barabanov // Automation of technological production in mechanical engineering: interuniversity. Sat. scientific tr. / VolgSTU. – Volgograd, 1999. – pp. 67–73. 3. A.S. No. 1567899 USSR, MKI G01M3/26. Method of testing a two-cavity product for tightness / G. P. Barabanov, L. A. Rabinovich, A. G. Suvorov [etc.]. – 1990, Bull. No. 20. UDC 62–503.55 N. I. Gdansky, A. V. Karpov, Ya. A. Saitova INTERPOLATION OF TRAJECTORY WHEN CONTROLING A SYSTEM WITH ONE DEGREE OF FREEDOM GOUVPO Moscow State University of Environmental Engineering E-mail: [email protected] When using forecasting in the control of single-degree systems, it becomes necessary to construct a trajectory passing through previously measured nodal points. A piecewise polynomial curve consisting of Fergusson splines is considered. The article presents a method for partial calculation of spline coefficients, which requires significantly fewer computational operations compared to the traditional method. Keywords: load models, forecasting, splines. It is necessary to construct the trajectory, which passing through the previously measured nodal points, when using the prediction in control systems. For this purpose, polynomial piecewise curve consisting of Ferguson spline is used. This paper presents a method for calculating the coefficients of these splines, which require significantly fewer computational operations than the traditional method. Keywords: model the external load acting, prediction, splines. In digital motion control systems in single-degree systems, it is proposed to model the external load M (t, φ (t)) along the coordinate φ in the form of a set of constant coefficients M k . The instantaneous quantity M (t, φ (t)) is the scalar product M (t, ϕ (t)) = M k, ϕk (t), in which the vector () torus ϕk (t) depends only on t and derivatives of ϕ with respect to t. With this method of representing the external load, to calculate the control action in this system, the work A that the drive must perform at a given control period is used: Ai = ti +1 ∫ (M k, ϕk (t))ϕ′(t)dt. ti As follows from general view formulas for M and Ai, they clearly do not contain the function ϕ (t), but only its derivatives. This general property of the solution method can be used to simplify the auxiliary task of interpolating the trajectory of a shaft along its node points. Let us assume that an ordered array of trajectory nodes Pi = (ti, ϕi) (i = 0, ..., n) is given. To construct a piecewise polynomial curve ϕ (t) of the second degree of smoothness passing through
Chapter 1 Analysis of the state of the problem of automation of tightness control and formulation of the research problem.
1.1 Basic terms and definitions used in this study.
1.2 Features of monitoring the tightness of gas fittings.II
1.3 Classification of gas testing methods and analysis of the possibility of their use for monitoring the tightness of gas fittings.
1.4 Review and analysis of automatic leak testing using the manometric method.
1.4.1 Primary transducers and sensors for automatic leakage monitoring systems.
1.4.2 Automated systems and leakage monitoring devices.
Purpose and objectives of the study.
Chapter 2 Theoretical study of the manometric method of leak testing.
2.1 Determination of gas flow regimes in test objects.
2.2 Study of the compression method of testing for leaks.
2.2.1 Study of time dependencies when monitoring tightness using the compression method.
2.2.2 Study of the sensitivity of tightness control using the compression method with cutoff.
2.3 Study of the comparison method with continuous supply of test pressure.
2.3.1 Scheme for monitoring tightness using a comparison method with continuous supply of test pressure.
2.3.2 Study of time dependencies when monitoring tightness using the comparison method.
2.3.3 Study of the sensitivity of tightness control by comparison with continuous supply of test pressure.
2.3.4 Comparative assessment of the sensitivity of tightness control using the compression method with cutoff and the comparison method.
Conclusions to Chapter 2.
Chapter 3 Experimental study of the parameters of leakage control circuits performed based on the comparison method.
3.1 Experimental setup and research methodology.
3.1.1 Description of the experimental setup.
3.1.2 Methodology for studying leakage monitoring schemes.
3.2 Experimental study of the leak control scheme based on the comparison method.
3.2.1 Determination of the characteristic p = /(/) of the lines of the tightness control circuit.
3.2.2 Research of the time characteristics of the lines of the tightness control circuit using the comparison method.
3.2.3 Study of the static characteristics of the measuring line of the tightness control circuit.
3.3. Experimental study of a leak testing device based on the comparison method.
3.3.1 Study of a model of a device for leak testing with a differential pressure sensor.
3.3.2 Assessment of the accuracy characteristics of devices for leak testing, performed according to the comparison scheme.
3.4 Probabilistic assessment of the reliability of sorting products when monitoring tightness using the comparison method.
3.4.1 Experimental study of the distribution of the pressure value equivalent to the leakage of test gas in a batch of products.
3.4.2 Statistical processing of the results of the experiment to assess the reliability of sorting.
4.3 Development of leak sensors with improved performance characteristics.
4.3.1 Design of the leakage sensor.
4.3.2 Mathematical model and algorithm for calculating the leakage sensor.
4.4 Development of an automated stand for leak testing
4.4.1 Design of an automated multi-position stand.
4.4.2 Selection of parameters for leakage control circuits.
4.4.2.1 Methodology for calculating the parameters of the tightness control circuit using the compression method with cutoff.
4.4.2.2 Methodology for calculating the parameters of the tightness control circuit using the comparison method.
4.4.3 Determination of the performance of an automated stand for leak testing.
4.4.4 Determination of parameters of sealing seals for an automated stand.
4.4.4.1 Calculation method for a sealing device with a cylindrical collar.
4.4.4.2 Method for calculating the mechanical ring seal.
Introduction of the dissertation (part of the abstract) on the topic “Automation of tightness control of gas fittings based on the manometric test method”
An important problem in a number of industries is increasing requirements for the quality and reliability of products. This creates an urgent need to improve existing ones, create and implement new methods and means of control, including tightness control, which relates to flaw detection - one of the types of quality control of systems and products.
In the industrial production of shut-off and distribution valves, in which the working medium is compressed air or other gas, existing standards and technical conditions for its acceptance usually regulate one hundred percent control of the “tightness” parameter. The main unit (working element) of such valves is a movable “plunger-body” pair or a rotary valve element, which operate over a wide pressure range. To seal gas fittings, various sealing elements and lubricants (sealants) are used. During the operation of a number of gas fitting designs, a certain leakage of the working medium is allowed. Exceeding the permissible leakage due to poor-quality gas fittings can lead to incorrect (false) operation of the production equipment on which it is installed, which can cause a serious accident. In household gas stoves, increased leakage of natural gas can cause a fire or poisoning of people. Therefore, exceeding the permissible leakage of the indicator medium with appropriate acceptance control of gas fittings is considered a leak, i.e., a defective product, and eliminating defects increases the reliability, safety and environmental cleanliness of the entire unit, device or device in which the gas fittings are used.
Monitoring the tightness of gas fittings is a labor-intensive, time-consuming and complex process. For example, in the production of pneumatic mini-equipment, it takes up 25-30% of the total labor intensity and up to 100-120% of the assembly time. This problem can be solved in large-scale and mass production of gas fittings by using automated methods and control tools, which should ensure the required accuracy and productivity. In real production conditions, solving this problem is often complicated by the use of control methods that provide the necessary accuracy, but are difficult to automate due to the complexity of the method or the specifics of the test equipment.
About ten methods have been developed for testing the tightness of products using only a gaseous test medium, for the implementation of which over a hundred different methods and means of control have been created. The development of modern theory and practice of tightness control is devoted to the studies of A. S. Zazhigin, A. I. Zapunny, V. A. Lanis, L. E. Levina, V. B. Lembersky, V. F. Rogal, S. G. Sazhina. , Tru-shchenko A. A., Fadeeva M. A., Feldmana L. S.
However, there are a number of problems and limitations in the development and implementation of leak control means. Thus, most high-precision methods can and should be applied only to large-sized products in which complete tightness is ensured. In addition, restrictions of an economic, design nature, environmental factors, and safety requirements for operating personnel are imposed. In serial and large-scale production, for example, of pneumatic automation equipment, gas fittings for household appliances, in which a certain leakage of the indicator medium is allowed during acceptance tests and, therefore, the requirements for control accuracy are reduced, the possibility of its automation and, on this basis, ensuring high productivity of the corresponding control and sorting equipment, which is necessary for 100% product quality control.
An analysis of the features of the equipment and the main characteristics of the gas tightness testing methods most used in industry allowed us to conclude that the use of the comparison method and the compression method, which implement the manometric method, is promising for automating the tightness control of gas fittings. In the scientific and technical literature, little attention has been paid to these testing methods due to their relatively low sensitivity, but it is noted that they are most easily automated. At the same time, there are no recommendations for the selection and calculation of parameters of leakage monitoring devices performed according to a comparison scheme with a continuous supply of test pressure. Therefore, research in the field of gas dynamics of blind and flow-through tanks, as elements of control circuits, as well as techniques for measuring gas pressure as a basis for creating new types of converters, sensors, devices and systems for automatic control of the tightness of products, promising for use in gas production, is relevant and important. fittings.
When developing and implementing automated leakage monitoring devices, an important question arises about the reliability of the control and sorting operation. In this regard, the dissertation carried out a corresponding study, on the basis of which recommendations were developed that make it possible, during automatic sorting according to the “tightness” parameter, to exclude defective products from entering suitable ones. Another important issue is ensuring the specified performance of automated equipment. The dissertation provides recommendations for calculating the operating parameters of an automated stand for leak testing depending on the required performance.
The work consists of an introduction, four chapters, general conclusions, a list of references and an appendix.
The first chapter discusses the features of monitoring the tightness of gas fittings, which allow a certain leakage during operation. A review of gas leak testing methods, classification and analysis of the possibility of their use for automating the control of gas fittings is given, which made it possible to select the most promising - the manometric method. Devices and systems that provide automation of tightness control are considered. The goals and objectives of the study are formulated.
The second chapter theoretically examines two methods of tightness control that implement the manometric method: compression with pressure cut-off and a comparison method with continuous supply of test pressure. Mathematical models of the methods under study were determined, on the basis of which studies of their time characteristics and sensitivity were carried out under different gas flow regimes, different line capacities and pressure ratios, which made it possible to identify the advantages of the comparison method. Recommendations are given for the selection of parameters for tightness control circuits.
In the third chapter, the static and temporal characteristics of the lines of the tightness control circuit are experimentally studied using a comparison method at various values of leakage, line capacity and test pressure, and their convergence with similar theoretical dependencies is shown. The performance of the device for leak testing, made according to the comparison scheme, was experimentally tested and the accuracy characteristics of the device were assessed. The results of assessing the reliability of sorting products according to the “tightness” parameter and recommendations for setting up the corresponding automated control and sorting devices are presented.
The fourth chapter provides a description of typical automation schemes for the manometric test method and recommendations for the design of automated equipment for leak testing. The original designs of a leakage sensor and an automated multi-position stand for leakage control are presented. Methods for calculating leakage control devices and their elements, presented in the form of algorithms, are proposed, as well as recommendations for calculating the operating parameters of a control and sorting stand depending on the required performance.
The Appendix presents the characteristics of gas leak testing methods and time dependencies for possible sequences of changes in gas flow regimes in a flow-through container.
Similar dissertations in the specialty "Automation and control of technological processes and production (by industry)", 05.13.06 code HAC
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Conclusion of the dissertation on the topic “Automation and control of technological processes and production (by industry)”, Barabanov, Viktor Gennadievich
4. The results of a study of tightness control schemes based on a comparison method with a continuous supply of test pressure revealed a discrepancy between theoretical and experimental characteristics in their working areas of no more than 5%, which made it possible to determine the dependencies for selecting the operating parameters of the corresponding control and sorting devices.
5. An experimental study of a prototype model of a device for monitoring tightness at a leakage value and test pressure corresponding to the technical characteristics of serial pneumatic equipment confirmed the possibility of creating automated control and sorting devices based on the comparison method, the error of which does not exceed 3.5%, and the sensitivity corresponds to the established sensitivity range for the manometric method of leak testing.
6. A method for probabilistic assessment of the reliability of sorting products according to the “tightness” parameter has been determined, and on its basis recommendations have been proposed for setting up automated control and sorting devices based on the comparison method.
7. Standard automation schemes for the manometric method of leak testing and recommendations for the design of automated equipment for leak testing are proposed.
8. A design of a tightness sensor with improved performance characteristics has been developed, protected by RF patent No. 2156967, a mathematical model and a method for its calculation have been proposed, which makes it possible to evaluate the characteristics of sensors of this type at the design stage.
9. The design of an automated multi-position test stand for leak testing has been developed, protected by RF patents No. 2141634, No. 2194259, and recommendations for determining the operating parameters of the stand depending on the required performance; a method for calculating a leak-tightness monitoring device using a comparison method with a continuous supply of test pressure, which is used in the design of the stand, and methods for calculating two types of sealing devices that ensure reliable installation of the tested products in the working positions of the stand are proposed, which expands the capabilities of designers of automated equipment for leak-tightness control.
10. All methods for calculating devices used to automate leakage testing are presented in the form of algorithms, which, together with their standard diagrams and designs, makes it possible to create CAD equipment for automating the manometric method of leakage testing.
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