Connecting the pressostat to the compressor and its adjustment

One of the primary factors that indicate the functionality of air compressors is the operating pressure. In simpler terms, this refers to the degree of air compression generated in the receiver, which needs to be maintained within a specific range. It can be quite inconvenient to manually monitor this using a pressure gauge, which is why the responsibility of maintaining the desired compression level in the receiver is entrusted to the compressor automation unit.

Design and principle of operation of the automation unit

To maintain a specific pressure level in the receiver, most air compressors are equipped with an automation unit known as a pressostat. This component is responsible for turning the motor on and off at the appropriate time, ensuring that the compression level in the storage tank does not exceed or fall below the desired level.

The pressure switch for the compressor consists of several elements, including terminals that are used to connect the relay electrical cables.

Additionally, springs are installed on the adjusting screws, and the compression force of these springs determines the pressure level in the receiver.

1. The diaphragm is located under the spring and is compressed by compressed air.
2. The start button is designed for initiating and forcefully stopping the unit.
3. The connection flanges can range from 1 to 3. They are used to connect the compressor inclusion relay to the receiver, as well as to connect a safety valve and pressure gauge.

In addition to that, additional features can be added to the compressor automation.

1. The relief valve is designed to release pressure after forcefully stopping the engine, making it easier to restart.
2. The thermal relay protects the motor windings from overheating by limiting the amperage.
3. The time relay is installed on compressors with a three-phase motor. It disconnects the starting capacitor a few seconds after the motor starts.
4. Within the transmission system, there is a component called the gearbox. Placed on this specific part are pressure gauges that serve the purpose of measuring the air pressure. The reducer incorporated into the system enables the adjustment of the air compression to the desired level before it enters the hose.

The pressostat operates by following this principle. Once the compressor engine is running, the pressure inside the air receiver begins to increase. Since the air pressure regulator is connected to the receiver, the compressed air flows from the receiver into the diaphragm block of the relay. The diaphragm is pushed upwards by the air and compresses the spring. As the spring is compressed, it activates the switch, causing the contacts to open, resulting in the motor of the unit ceasing. When the compression level in the receiver drops, the diaphragm located in the pressure regulator bends downwards. This releases the spring, and the switch closes the contacts, restarting the engine.

Schemes for connecting the pressostat to the compressor

There are two sections to the relay connection for controlling air compression. Firstly, there is the electrical connection of the relay to the unit. Secondly, there is the connection of the relay to the compressor through connecting flanges. The specific pressostat connection schemes vary depending on whether the compressor is equipped with a 220V or 380V motor. By following these schemes and having basic electrical engineering knowledge, it is possible to connect the relay manually.

In order to link the automation to the compressor powered by the 380 V network, a magnetic starter is utilized. The schematic below showcases the connection of the automatics to the three phases.

In the provided illustration, the circuit breaker is denoted by the characters "AB", and the magnetic starter is represented by the label "KM". From this configuration, it can be deduced that the relay is adjusted to activate at a pressure of 3 atm and deactivate at a pressure of 10 atm.

Connection of the pressostat to 220 V network

The relay is linked to a one-phase grid based on the provided diagrams below.

Displayed below are different pressostat models from the RDK series, which can be connected to the compressor’s electrical section in the following manner:

Pro tip! Inside the pressostat cover, you will find two rows of terminals. Typically, there will be a label indicating "Motor" or "Line" to indicate the corresponding contacts for connecting the motor and the power supply.

Connecting the pressostat to the unit

It is quite easy to connect the pressure switch to the compressor.

1. Attach the pressostat to the receiver connection by screwing it into the threaded center hole. To ensure a tight seal, it is recommended to use fum-tape or liquid sealant on the threads. If necessary, the relay can be connected to the receiver using a reducer.
2. If available, connect a relief valve to the smallest outlet of the relay.
3. For the other outputs of the relay, you can either connect a pressure gauge or a safety relief valve. It is important to always install the safety relief valve. If a pressure gauge is not needed, the free outlet of the pressostat should be plugged with a metal plug.
4. Next, connect the wires from the power supply and the engine to the sensor contacts.

Once the pressostat is fully connected, it will need to be adjusted for proper operation.

As previously mentioned, the pressostat shuts off the motor of the unit after achieving a specific level of air compression in the receiver. Conversely, when the pressure decreases to the switch-on limit, the relay restarts the motor.

Note: By default, the relays of both single-phase and 380 V units are preconfigured at the factory. The variance between the lower and upper limits for motor start-up does not exceed 2 bar. It is strongly recommended that the user does not modify this value.

However, there are often situations where it becomes necessary to modify the factory settings of the pressostat and adjust the compressor pressure according to personal discretion. Only the lower threshold for switch-on can be modified, as increasing the upper threshold for switch-off will result in the release of air through the safety valve.

Make the necessary changes to the pressure of the compressor as described below.

1. Start the device and record the pressure gauge reading when the motor turns on and off.
2. Make sure to disconnect the device from the power source and remove the cover from the pressure switch.
3. After removing the cover, you will find two bolts with springs. The larger bolt is often labeled with the letter "P" with "-" and "+" symbols, and it controls the upper pressure. When this pressure is reached, the device will turn off. To increase the air compression, turn the regulator towards the "+" symbol, and to decrease it, turn it towards the "-" symbol. It is advisable to make a half turn in the desired direction initially, then turn on the compressor and use a pressure gauge to check the pressure increase or decrease. Take note of the values at which the motor shuts off.
4. Moreover, it is essential to adjust the gearbox if it is present in the system. The gearbox needs to be configured at a compression level that corresponds to the operational pressure of the pneumatic tool or machinery linked to the system.