Pressure relays for compressors: types and description of installation
The pressure switch is a design, which is designed to automatically turn on and off the electric motor of the compressor. It is often called a telepressostat or compressor pressure switch. The relay is most often used in a design of management of reciprocating compressors for preservation in the receiver of the necessary working pressure of air.. Rarely can be seen on screw compressors, but there is usually another automation.
The principle of operation of relays for compressors
Given the amount of pressure in the pneumatic system, the relay opens or closes the voltage circuit, opening, so, compressor at insufficient pressure, and disabling when the set value is reached. This is a normal principle of operation, which is based on the installation in the circuit of a normally closed circuit to control the motor.
There are also models with the opposite principle of operation, that is, when the minimum pressure in the circuit is reached, the relay will shut down the electric motor, at the maximum - to include. This system is assembled with a normally open electrical circuit.
The working system is springs with different levels of rigidity, responsive to changes in the air pressure system. Forces are compared during work, which appear as a result of the force of elastic deformation of the springs and the pressure of the compressed air of the installation. When the pressure changes, the spring mechanism is activated, and the relay turns the electrical circuit on or off.
Relay components
The air pressure switch can be additionally equipped:
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Unloading valve, which is located between the check valve on the compressor and the compression chamber of the installation. If the engine stops, then the unloading valve works and removes excess pressure from the piston unit. Upon further acceleration or start of the electric motor, the valve closes with the generated pressure, significantly facilitating the start of the installation from the off position. There is also a discharge valve with delayed inclusion. It additionally helps the engine during startup, remaining in the open state until the set parameter is reached (about 2 atmosphere) in the system. This time is enough, so that the electric motor reaches the maximum moment, twisting, and revs.
- Mechanical switch. Needed to enable and disable the automatic system function. Switch, usually, has two provisions: "ON" and "OFF". In the "ON" mode, the compressor is automatically connected to the mains and switched off in accordance with the specified parameters of the minimum and maximum air pressure in the system. In the "OFF" position, no power is supplied to the electric drive.
- Thermal relay to protect the electric motor. It limits this figure, as the force of the current supplied, to prevent the engine windings from burning out. The required value of the current can be set using a special regulator. If this value is exceeded, the engine will be disconnected from the mains immediately.
- Safety valve. This device will protect the system if the relay does not work properly. When the pressure rises above the allowable value, but the relay does not turn on, then the safety valve is triggered, it will relieve the pressure. This will avoid unwanted consequences and serious accidents in case of failure of the control circuit.
Wiring diagram
Air relays for compressors are made for various load connection schemes. When the drive electric motor is a single-phase motor, then put the relay on 220 Volt, having two groups of connections. If, if the load is in three phases, then the model is installed on 380 Volt with three electronic contacts, to turn off all at once 3 phases. It is desirable not to allow such a situation, how to connect a three-phase motor using a compressor relay on 220 Volt, as in this case one phase of an electric network is not disconnected from loading.
Connection flanges
Some manufacturers complete the equipment with additional connection flanges. Usually, their number is not more than three, and the size of the hole 1/4 in. This version makes it possible to connect some additional devices to the compressor in parallel, example, safety valve, pressure gauge or fuse valve.
Installation of the pressure relay
The question often arises: how to connect a relay to a compressor? You need to start the device:
- Connect the relay to the receiver through the main outlet.
- For relays with flanges connect, if needed, pressure gauge.
- If needed, then connect to the compressor flanges the safety and relief valve.
- Unused connection channels must be plugged.
- Connect the electric motor control circuit to the relay contacts. Current, which consumes the motor, should not be more than the allowable voltage of the relay contacts. Low power motors can be connected directly, and in other cases it is necessary to put in addition the magnetic starter of necessary size.
- Set the maximum and minimum pressure in the system with the adjusting screws.
Much attention needs to be paid to this, that the adjustment of the compressor relay must be under pressure, but the motor power must be switched off.
Relay adjustment
The pressure switch is sold already regulated by the manufacturer and does not require user adjustment. But there are cases, when you just need to change the factory settings. To start, you need to know the operating range of the compressor. On the manometer it is necessary to find out, at what pressure the relay will turn on the engine, and when to turn off.
Then, when the required values are defined, be sure to disconnect the compressor from the mains. After, when the unit is disconnected, remove the relay cover. Under the top are two bolts: large and slightly smaller.
The larger screw is often used to adjust the upper pressure, that is, the maximum, when the motor is switched off. He, usually, marked with the letter "P" and an arrow with pointers "plus" and "minus". To increase the shut-off rate, turn the screw in the direction of the "plus" pointer, to reduce, vice versa, towards "minus".
Screw, which is less, sets the difference between on and off pressure. And is indicated by the designation "?P "and arrow. Usually, the magnitude of this pressure difference has 1,5-2 there is. The higher the indicator "?P», the less often the engine will start, but the pressure drop in the pneumatic system increases.
In the end I would like to say, that the air compressor is considered a universal tool, without which it is quite difficult to do when carrying out any repair and construction work.
Pneumatic equipment is much safer, more convenient and easier than electric or gasoline. There are also a huge number of additional devices for working with compressed air: flushing gun, gun for pumping tires, paint gun, purge gun, sandblasting nozzle for the compressor, extension cord and so on. Thanks to the pressure switch the system can work automatically, maintaining the required pressure in the receiver.
