Let's imagine that the pipes of two injection compressors are installed in parallel (Fig. 21.10). In this case, compressor C1 is running, and C2 is stopped. According to this scheme, part of the oil pumped by C1 accumulates in the compressor head C2, where the refrigerant enters and condenses. During a long stop of C2, the temperature of its head is equal to the temperature environment.
If the discharge valve C2 is leaking, due to the pressure difference in it, part of the liquid (item 1) enters the cavity of the C2 cylinder and a high probability of water hammer occurs during startup. To discourage this phenomenon, it is necessary to connect the discharge pipes of two parallel mounted compressors according to the indicated diagram (Fig. 21.11).
In some cases, the installation is carried out with a lyre-shaped compensator (Fig. 21.12) running along the ground. This compensator (item 1) is located in close proximity to the compressors and its temperature is equal to the ambient temperature. It is a liquid trap that works equally for both oil and liquid refrigerant, and also allows you to reduce vibrations and compensate for thermal deformations of pipes. Special attention should be paid to leveling the oil level (item 2).
If the connection methods we have considered almost completely eliminate the accumulation of oil in the head of a stopped compressor, then they do not exclude the entry of refrigerant vapors into it. For greater confidence, check valves are installed on the discharge pipes of these compresses. But this method has its own Negative consequences, and in order to achieve the desired result, some safety measures must be taken.
The installed check valves must have the lowest hydraulic resistance, since by increasing the pressure loss on the discharge line, they will cause an increase in the temperature of the discharge vapors, and therefore a decrease in cooling capacity. Perform installation check valve should be done with extreme care and attention. If a small foreign particle (a drop of solder, copper shavings...) gets under the check valve seat, it will disrupt its tightness and performance.
Another characteristic of check valves is the ability to “pop” as a result of pulsating discharge pressure or due to close installation relative to the discharge pipe, which can lead to their rapid destruction as a result. Based on this, the check valve on the discharge line is installed away from the compressor (preferably after the muffler) for greater efficiency. This makes it possible to retain foreign particles and reduce pressure pulsations.
The muffler must be installed in such a way that the oil can circulate freely. For this purpose, the word “Tor” (Up) is engraved on its outer surface. When installing a check valve and muffler, it is also necessary to take into account the direction of the fluid and follow the developer’s instructions (Fig. 21.13).
Valve failure due to water hammer is classified as a “too weak compressor” type fault.
Please explain why KT-602-1 describes the simplest parallel connection of the crankcases of two compressors with a tube to equalize the oil level without using an oil level regulator, and nothing is said about equalizing the gas pressure, i.e. a tube is supposed to be mounted above the oil level and connects two compressors while equalizing the gas pressure. And please answer how reliable will be the control of sequential operation of compressors without “logic” by means of RD, i.e. one of the compressors will always turn on first and, accordingly, work more. Thank you!
07 07 2012 // Nail Alekperov
Answer:
Are you sure that you saw this diagram exactly in? These instructions are for parallel connection of OCTAGON series compressors. For them, connecting the crankcases with any tubes is not at all desirable.
By the way, this manual has already been updated to KT-602-2 Parallel compounding of OCTAGON compressors.
Please send me a diagram that interests you. Let's discuss.
It is necessary to connect two 4DC-5.2 compressors in one unit for the minus chamber (R404a) consumer one point (evaporator). The customer does not want to equip the compressor with oil level regulators and other additional features. lotions (it’s still a bug), what to do and how to get out of this situation, thank you in advance
09 07 2012 // Nail Alekperov
Answer:
The most appropriate solution for your installation is the 44DC-10.2 tandem, or an already assembled unit based on the LH124/44DC-10.2 tandem
If your installation has a small length of pipes, there are all the necessary slopes and oil lifting loops, and the evaporator is defrosted regularly, then even with parallel connection two 4DC-5.2, there is no need to install either an oil separator, or an oil level control system in the crankcases, or any equalization tubes connecting the compressor crankcases. You just need to make a symmetrical suction manifold, see instructions.
Re(1): Parallel connection
Forgive me for being intrusive, but what to do if one of the compressors is down? Do you think that with the correct symmetry of the manifold, etc., I can avoid oil carryover from an inoperative compressor? The length of the pipeline is only 4 meters, the controller has an auto defrost function, it was supposed to install an oil separator on the discharge and a liquid separator on the suction, the sequential switching on of the compressors is regulated by the RD, the fans on the condenser are also turned on and off by the RD. Thank you
09 07 2012 // Nail Alekperov
Answer:
Yes, both in tandem and in parallel connection, with the correct symmetry of the collector, when one of the compressors is idle, oil does not carry over from it - where?
If the evaporator is selected correctly, i.e. its performance corresponds to that of the compressor if regular evaporator defrosts are carried out, i.e. its complete freezing is not allowed; if a expansion valve with an MOP or EEV point is used, with overheating control in all operating modes, then the compressors will not be filled with liquid refrigerant, i.e. There is no need to install a liquid suction accumulator.
Oil circulates through the system - there is nothing wrong with that. In your installation there is a short and unbranched circuit, i.e. the oil cannot lie somewhere. Why then spend money on an oil separator, an oil receiver and a system for regulating oil levels in compressor crankcases?
Re(3): Parallel connection
Following your advice, the guys and I assembled a unit of two Bitzer 7.2 compressors without oil level regulators, but the oil still goes somewhere, especially from the first compressor, the suction pressure is high 2.5 on temperature regime We don’t go out, I think the evaporator is flooded with oil?! I am attaching a photo Help please!
07/18/2012 // Nail Alekperov
Answer:
Thanks for your photo
Your suction manifold looks nice. And the pumping turned out to be scary!
For an example of the correct location of the discharge pipes, see the photo and the answer to the question
Budget models of air compressors are not always equipped with a pressure switch, since similar devices are installed on the receiver. Therefore, manufacturers of this equipment believe that visual monitoring of the pressure developed by the compressor based on pressure gauge readings is quite sufficient. At the same time, during long-term work, in order to avoid engine overheating, it is advisable to install a pressure switch on the compressor. Then the drive will turn on and off automatically.
Design and diagram of a pressure switch for the compressor
All compressor pressure switches are divided into two types:
- Switching off the compressor electric motor when the air pressure in the network exceeds permissible limits (such designs are called normally open);
- Turning on the compressor electric motor when the pressure in the network decreases below permissible limits (such designs are called normally closed).
The actuator element of the pressure switch for the compressor is springs, the compression force of which is changed by a special screw. In the factory settings, the compression force of the springs is usually set to a pressure in the pneumatic network from 4 to 6 atm, as reported in the user manual.
Since the rigidity and flexibility of spring elements depend on the ambient temperature, all designs of industrial pressure switches are designed for stable operation in the temperature range from -5 to +80ºС.
The design of the pressure switch includes two mandatory subassemblies - an unloading valve and a mechanical switch.
The unloading valve is connected to the air supply line between the receiver and the compressor. It controls the operation of the electric motor. If the compressor drive is turned off, the unloading valve located on the receiver discharges excess compressed air (up to 2 atm) into the atmosphere, thereby unloading the moving parts of the compressor from the excess force that they will have to develop when the compressor is turned on again. This prevents critical overload of the engine in terms of permissible torque. When the unloaded engine starts, the valve closes and does not create unnecessary load on the drive. A mechanical switch performs the stand by function, preventing accidental starting of the engine. After pressing the button, the drive is turned on and the compressor operates in automatic mode
. If the button is turned off, the compressor engine will not start even if the pressure in the pressure pneumatic network is lower than required.
In order to increase work safety, industrial designs of compressor pressure switches are also equipped with a safety valve. It is useful, for example, in case of sudden engine stop, piston failure or other emergency situation.
Optionally, a thermal relay can be installed in the pressure switch housing, with the help of which the current strength in the primary circuit is monitored. If for some reason this parameter increases, then, in order to avoid overheating and subsequent breakdown of the windings, the thermal relay will turn off the electric motor.
How to connect and configure a pressure switch? In general schematic diagram
In the compressor unit, the pressure switch is located between the unloader valve and the secondary engine control circuit. Typically the pressure switch is equipped with four threaded heads. One of them is intended for connecting the device to the receiver, and the second is for connecting a control pressure gauge. One of the remaining connectors can be used to install a safety valve, and the remaining one can be fitted with a regular ¼-inch threaded plug. The presence of a free connector allows you to install the control pressure gauge in a place convenient for the user.
- The pressure switch is connected in the following sequence:
- Connect the device to the unloading valve of the receiver.
- Connect to the terminal contacts of the electric motor control circuit (taking into account the selected connection diagram - normally open or normally closed contacts). When the voltage in the network fluctuates, the connection is made not directly, but through a surge protector. This is also required when the power for which the contacts are designed exceeds the motor load current.
- If necessary, use the adjusting screws to adjust the relay to required values compressed air pressure.
When connecting, you need to check whether the network voltage corresponds to the factory settings of the compressor pressure switch. For example, in a three-phase network with a voltage of 380 V, the relay must have a three-contact group (two phases + zero), and for a voltage of 220 V - a two-contact group.
The adjustment is made when the receiver is at least two-thirds full. To perform this operation, the relay is disconnected from the power supply, and, by removing the top cover, the compression of the two springs is changed. The adjusting screw, on which the axis of the larger diameter spring is mounted, is responsible for the upper limit of the working pressure. On the board next to it, the generally accepted pressure symbol (P - pressure) is usually indicated, and the direction of rotation of the screw by which this pressure is reduced or increased is also indicated. The second, smaller adjustment screw is responsible for setting the required pressure range (difference). It is marked symbolΔР, and is also equipped with a rotation direction indicator.
To reduce setup time, in some designs the adjusting screw for changing the upper pressure limit is moved outside the pressure switch housing. The result is monitored using the pressure gauge readings.
DIY pressure switch
With known skills, as well as the presence of a working thermostat from a decommissioned refrigerator, a pressure switch can be made independently. True, it will not have any special practical capabilities, since the ability to maintain upper pressure is limited by the strength of the rubber bellows.
Thermal relays of the KTS 011 type are most convenient for conversion into a compressor pressure switch, since they have a strictly reverse sequence of operation: when the temperature in the refrigeration chamber increases, the relay turns on, and when it decreases, it turns off.
The essence and sequence of work is as follows. After opening the lid, set the location the desired group contacts, for which it is enough to ring the circuit. First, the connection between the thermal relay and the compressor is finalized. To do this, the outlet pipe, together with the control pressure gauge, is connected to the unloading valve, and the contact groups are connected to the terminals of the electric motor circuit. An adjusting screw will be found under the thermostat cover. When the compressor is turned on (the receiver should be filled to no more than 10...15% of its nominal volume), the screw is rotated sequentially, monitoring the result using the pressure gauge. To set the lower position (which determines the minimum air pressure), you will have to gradually move the face button rod. To do this, the cover is installed in place, and the adjustment is actually made blindly, since there is nowhere to connect the second pressure gauge.
For safety reasons, the pressure adjustment range using such a thermal relay cannot be more than 1...6 atm, however, using devices with a more durable bellows, you can increase the upper range to 8...10 atm, which in most cases is quite sufficient.
After checking the functionality of the relay, the capillary tube is cut off and the refrigerant contained there is released. The end of the tube is soldered into the unloading valve.
Next, work is carried out to connect a homemade pressure switch to the compressor control circuit: using a nut, the relay is attached to the control board, a thread is made on the rod, and a lock nut is screwed on, by rotating which you can adjust the limits of air pressure change.
Considering that the contact group of any thermal relay from a refrigerator is designed for fairly high currents, in this way it is possible to switch circuits of significant power, including secondary compressor motor control circuits.
Air hose designed to connect the compressor with a paint sprayer and water-oil separating filters. There are several types of air hoses, differing in material of manufacture and connection diagram. In order to choose a name that suits you, you must have certain knowledge of their properties and design features.
The most common compressor hoses used in garage painting are:
- reinforced rubber;
- reinforced plastic.
Technically and morally obsolete twisted hoses for compressors, which can still be found in the garages of many home craftsmen, are in no way recommended to be used. This is due, first of all, to their small cross-section, amounting to only 5-6 mm. In addition, old hoses are very unreliable and can break at the most inopportune moment, completely blocking air access to the spray gun. As a result, further coloring becomes impossible. That is why it is necessary to make a choice exclusively in favor of modern products. Let's look at its main advantages and disadvantages.
Rubber-reinforced hose durable, wear-resistant, suitable for use with oxygen cylinders. Its only drawback can be considered only its relatively large weight.
Plastic-reinforced hose costs less than rubber-reinforced ones, weighs slightly less. Its main disadvantage is its high sensitivity to changes in ambient temperature. Yes, when low temperatures This hose hardens excessively, and at high temperatures it softens. As a result, its service life is reduced. Plastic-reinforced hoses are especially poorly resistant to direct sunlight, as a result of which their strength is reduced several times.
There are 2 types of practical and quick-release connectors designed to connect air hoses to compressors, moisture-oil filters and spray guns - fittings And fitting. They are inserted into each other according to the “fitting into fitting” scheme. In this case, hoses and a water-oil separating filter are equipped with a fitting, and a paint sprayer is equipped with a fitting.
If you purchased a moisture-oil separating filter without a fitting, you must select an inlet/outlet fitting for it that has an external thread for connection.
The hose connectors are secured using special clamp elements. When choosing these fasteners, you should not pay attention to the features of their design and appearance: The most important thing is that the connection does not “poison” the air.
One of the main indicators of air compressors is operating pressure. In other words, this is the level of air compression created in the receiver that must be maintained within certain range. It is inconvenient to do this manually, referring to the indicators of the pressure gauge, so the compressor automation unit is responsible for maintaining the required level of compression in the receiver.
To maintain the pressure in the receiver at a certain level, most air compressors have an automatic control unit, pressure switch
This piece of equipment turns the engine on and off at the right time, preventing the compression level in the storage tank from being exceeded or too low.
The pressure switch for the compressor is a unit containing the following elements.
In addition, automation for the compressor may have additions.
- Unload valve. Designed to relieve pressure after a forced stop of the engine, which makes it easier to restart.
- Thermal relay. This sensor protects the motor windings from overheating by limiting the current.
- Time relay. Installed on compressors with a three-phase motor. The relay turns off the starting capacitor a few seconds after the engine starts.
- Safety valve. If the relay malfunctions and the compression level in the receiver rises to critical values, then to avoid an accident it will work safety valve, releasing the air.
- Gearbox. On this element Pressure gauges are installed to measure air pressure. The reducer allows you to set the required level of compression of the air entering the hose.
Operating principle of the pressure switch as follows. After the compressor engine starts, the pressure in the receiver begins to increase. Since the air pressure regulator is connected to the receiver, the compressed air from it enters the membrane relay unit. The membrane bends upward under the influence of air and compresses the spring. The spring, compressing, activates the switch, which opens the contacts, after which the engine of the unit stops. When the compression level in the receiver decreases, the membrane installed in the pressure regulator bends down. At the same time, the spring opens, and the switch closes the contacts, after which the engine starts.
Diagrams for connecting the pressure switch to the compressor
The connection of the relay that controls the degree of air compression can be divided into 2 parts: the electrical connection of the relay to the unit and the connection of the relay to the compressor through the connecting flanges. Depending on which motor is installed in the compressor, 220 V or 380 V, there are different connection diagrams for the pressure switch. I am guided by these schemes, subject to availability certain knowledge
in electrical engineering, you can connect this relay with your own hands.
Connecting the relay to a 380 V network magnetic switch. Below is a diagram of connecting automation to three phases.
In the diagram, the circuit breaker is indicated by the letters “AB”, and the magnetic starter by “KM”. From this diagram it can be understood that the relay is set to a switch-on pressure of 3 atm. and shutdown - 10 atm.
Connecting the pressure switch to a 220 V network
The relay is connected to a single-phase network according to the diagrams given below.
These diagrams show various models of pressure switches of the RDK series, which can be connected in this way to the electrical part of the compressor.
Advice! Under the pressure cover there are 2 rows of terminals. Usually next to them there is the inscription “Motor” or “Line”, which, respectively, indicate contacts for connecting the motor and the electrical network.
Connecting the pressure switch to the unit
Connecting a pressure switch to a compressor is quite simple.
After the complete connection of the pressure switch is completed, it is necessary to configure it for proper operation.
Adjusting the compressor pressure
As mentioned above, after creating a certain level of air compression in the receiver, the pressure switch turns off the unit’s engine. Conversely, when the pressure drops to the switching limit, the relay starts the engine again.
Important! By default, relays, both single-phase devices and units operating from a 380 V network, already have factory settings. The difference between the lower and upper engine start threshold does not exceed 2 bar. This value It is not recommended for the user to change it.
But often situations that arise force you to change the factory settings of the pressure switch and adjust the pressure in the compressor at your discretion. You can only change the lower switching threshold, since after changing the upper switching threshold upward, the air will be released by the safety valve.
Pressure adjustment in the compressor is carried out as follows.
Besides everything, it is necessary adjust the gearbox, if it is installed on the system. It is necessary to set the compression level on the gearbox to a level that corresponds to the operating pressure of the pneumatic tool or equipment connected to the system.
