Pressure switch for compressor: device, marking + connection diagram and adjustment

The use of an air pneumatic relay allows you to automate the filling of the compressor receiver with compressed gas. The operator of equipment with a pressure switch does not need to monitor the process, trying to fix the limit parameters. As a result, engine damage is prevented. Significant results, right?

If you are planning to purchase a pressure switch for your compressor, then you have come to the right place. Here you will find a vast amount of extremely useful information about the principles of operation of the device, its configuration and connection methods.

We have described in detail the existing types of pneumatic relays. They provided options for connecting to a household and industrial network with extremely clear diagrams. We looked at typical breakdowns and ways to prevent them. The information and useful tips we provide are supplemented with graphic, photo and video applications.

Operating principle of a pressure switch

The name of the relay is determined by its purpose - controlling a piston compressor to maintain the required atmospheric pressure in the receiver. It is rarely found on a screw type device responsible for compressing and supplying air.

I take into account the magnitude of the pressing force in pneumatic automation; the device acts on the voltage line, closing or opening it. Thus, insufficient pressure in the compressor starts the motor, and when the required level is reached, it turns it off.

This standard operating principle, based on connecting a normal closed loop to a circuit, is used to control the motor.

The design of all ejectors contains a cylinder containing air at a certain pressure. Reducing it requires turning on the engine to replenish the supply. If the situation is the opposite and an excess is detected, the supply is stopped so that the container does not burst. These processes are controlled by a pressure switch

Modifications with the opposite operating algorithm are also presented: when reaching minimum values ​​in the compression circuit, the pressure switch turns off the electric motor, and at maximum values ​​it activates. Here the system operates in a normally open loop.

The operating system is made up of spring mechanisms with varying degrees of rigidity, reproducing the response to fluctuations in the air pressure unit.

During operation, the indicators formed as a result of the elastic force of tension or compression of the springs and the pressure of the atmosphere pressed by the device are compared. Any changes automatically activate the action of the spiral and the relay unit connects or disconnects the electricity supply line.

However, it is worth considering that the design of the review model does not provide for regulatory influence. Exceptional impact on the engine. In this case, the user has the opportunity to set a peak value, upon reaching which the spring will fire.

Complete set of compressor automation unit

The relay design is a small-sized block equipped with receiving pipes, a sensing element (spring) and a membrane. Mandatory subassemblies include an unloading valve and a mechanical switch.

The pressure switch sensing unit is made up of a spring mechanism, the compression force of which is changed by a screw. According to the factory standardized settings, the elasticity coefficient is set to a pressure in the pneumatic chain of 4-6 at, as reported in the instructions for the device.

Inexpensive models of ejectors are not always equipped with relay automation since such devices are mounted on the receiver. However, during long-term operation, to eliminate the problem of overheating of engine elements, it makes sense to install a pressure switch

The degree of rigidity and flexibility of the spring elements is subject to the temperature of the environment, therefore absolutely all models of industrial devices are designed for stable operation in an environment from -5 to +80 ºC.

The reservoir membrane is connected to the relay switch. During movement, it turns the pressure switch on and off.

The unloading unit is connected to the air supply line, which allows excess pressure to be released into the atmosphere from the piston compartment. This relieves the moving parts of the compressor from excessive force.

The unloading element is located between the ejector check valve and the compression block. If the motor drive stops working, the unloading section is activated, through which excess pressure (up to 2 atm) is released from the piston compartment.

With further start or acceleration of the electric motor, a pressure is created that closes the valve.This prevents overloading of the drive and simplifies starting the device in switched off mode.

There is an unloading system with a time interval of activation. The mechanism remains in the open position when the engine starts for a specified period. This range is enough for the engine to achieve maximum torque.

A mechanical switch is required to start and stop the automatic system options. As a rule, it has two positions: “on.” and "off". The first mode turns on the drive and the compressor operates according to the established automatic principle. The second one prevents accidental starting of the engine, even when the pressure in the pneumatic system is low.

Shut-off valves allow you to avoid emergency situations when elements of the control circuit fail, for example, a breakdown of the piston unit or a sudden stop of the motor

Safety in industrial structures must be at a high level. For these purposes, the compressor regulator is equipped with a safety valve. This ensures system protection in the event of incorrect relay operation.

In emergency situations, when the pressure level is higher than the permissible norm, and the telepressostat does not work, the safety unit comes into operation and vents the air. They operate according to a similar scheme safety valves in heating systems, the operating principles and devices of which are described in our recommended article.

Optionally, the viewing device can also be used as additional safety equipment. thermal relay. With its help, the strength of the supply current is monitored for timely disconnection from the network when parameters increase.

To avoid burnout of the motor windings, the power is turned off. The nominal values ​​are set using a special control device.

Types of pressure switch devices

There are only two variations in the design of the automatic compressor unit. The determination is made based on their operating principle. In the first version, the mechanism turns off the electric motor when the established limits of the air mass pressure level in the pneumatic network are exceeded. These devices are called normally open.

Schematic structure of a membrane pressure switch: 1 – pressure converter; 2 and 3 – contacts; 4 – piston; 5 – spring; 6 – membrane; 7 – threaded connection

Another model with the opposite principle - turns on the engine if a drop in pressure is detected below the permissible level. Devices of this type are called normally closed.

Structure of pneumatic relay symbols

The marking of the air pressure switch indicates the entire optional set of the device, design features, including information about the factory settings for the pressure differential.

Condor's production models offer a wide range of pressure control equipment. The MDR series is aimed at using ejectors of various powers

Let us examine the designations in more detail using the example of devices for air ejectors RDK – (*) (****) – (*)/(*):

• RDK – series of relays for compressors;
• (*) – number of threaded ports: 1 – one port with 1/4”NPT internal thread; 4 – four connectors;
• (****) - type of housing design: T10P - version 10 with a “lever” switch; T10K – “button” switch; T18P – execution 18 with a “switch” switch; T19P - 19 s;
• (*) – factory settings of the threshold response: 1 – 4…6 bar; 2 – 6…8 bar; 3 – 8…10 bar;
• (*) – diameter of the unloading valve: the absence of a symbol means a standardized parameter of 6 mm; 6.5 mm – 6.5 mm.

The difference between the minimum and maximum pressure thresholds is set by the manufacturer and, as a rule, has a value of 2 bar.

However, it is also possible to manually adjust the range of two values ​​– maximum and minimum, but only downwards.

The specifics of setting up pressure switches for pumping stations are outlined in next article, the contents of which we advise you to familiarize yourself with.

Air relay connection diagrams

The compressor pressure switch is manufactured for connection to electrical circuits of different loads. In accordance with the rating of the power supply line, the appropriate model of the relay unit is selected.

Option #1: to a network with a nominal value of 220 V

If the drive motor is a single-phase device, then a 220 V relay with two groups of contacts is installed.

To work with a single-phase load, manufacturers recommend equipping the unit using models of the RDK series: xT10R-x; xT10K-x; xT19P-x, since these devices have two contact groups

Option #2: to a three-phase network with a voltage of 380 V

For a three-phase load of a 380 V circuit, one of the options can be used: a modification of the relay for 220 V or 380 V, with three contact lines, to simultaneously disconnect all three phases.

Both methods have different schemes. Let's consider the first option:

To operate in a three-phase electrical circuit, a pressure switch RDK-xT18P-x is used. This model is equipped with three contacts and facilitates simultaneous switching of all phases

By choosing the second method, power is supplied from one phase (zero) and in this case the relay rating should be 220 V. For more details, see the following diagram:

It is allowed to use telepressostats of the RDK series: xT10R-x, xT10K-x and xT19P-x with a three-phase load, however, the use of such a circuit requires incomplete disconnection from the supply network. More specifically, one phase will be permanently connected to the load

After connecting to the power supply, you need to understand the additional capabilities provided in the air blocks for ejectors.

Installation of relays and auxiliary elements

In some modifications of pressure switches, you can find additional equipment in the form of flange connections, through which additional equipment is connected. These are mainly three-way parts, with a ¼-inch diameter.

By means of several flange connectors, additional elements can be introduced into the system: safety valve, pressure gauge and other necessary mechanisms

To put the device into operation, it must be connected to the receiver. Installation consists of the following steps:

1. The device is connected to the compressor through the main outlet.
2. A pressure gauge is connected to the device with flanges. There may also be other auxiliary mechanisms that require activation: a safety or unloading valve.
3. Channels that are not used for connection must be closed with plugs.
4. Next, according to the electrical diagram, the relay is connected to the contacts of the motor control circuit.

Motors with low power can be connected directly; in other cases, additional installation of an electromagnetic starter of appropriate power is required.

Before moving on to setting the threshold response parameters, it is worth paying attention to the operating conditions. First, adjustments are made under pressure. Secondly, the electrical supply to the engine must be cut off.

Adjustment and commissioning process

Factory set parameters do not always meet consumer requirements. In most cases, this is due to insufficient compression force at the highest point of disassembly.

The operating range of the pressure switch may also not be suitable. In this case, independent adjustment of the actuator will be relevant.

Standard factory settings: upper limit 2.8 atmospheres, lower limit 1.4 bar. The parameters are monitored visually using a pressure gauge included in the standard pressure switch kit. New models, for example, Italtecnica, have a transparent body and are equipped with a compression scale indicator directly on the relay

To begin setting the operating compression value, you will need to inspect the engraved plate, which indicates the parameters of the electric motor and compressor.

We only need the largest value that the device produces. This indicator indicates the maximum pressure force that can be set on the relay for the correct operation of the entire pneumatic system.

If you set the specified value (in the figure 4.2 atm), then taking into account all factors - differences in power supply, exhaustion of the service life of parts, etc. - the compressor may not reach the maximum pressure, and accordingly it will not turn off.

In this mode, the working elements of the equipment will begin to overheat, then deform and eventually melt.

The maximum ejector value must be taken into account when determining the maximum relay value. This indicator should be less than the rated pressure of the compressor. In this case, all elements of the system will work uninterruptedly

For reliable operation without shutdowns, it is necessary to set the highest shutdown pressure on the relay, which does not reach the nominal value engraved on the compressor, namely 0.4-0.5 atm lower. According to our example - 3.7-3.8 atm.

The pressure limits at which the compressor is turned on/off are regulated by a single bolt. In order not to make a mistake with the choice of direction for increasing/decreasing, arrows are placed on the metal base

Having determined the level that will be set, it is necessary to remove the relay housing. Under it there are two adjusting elements - a small and a large nut (in Figure 1.3).

Nearby there are arrow indicators for the direction in which the twists will be made - thereby compressing and unclenching the spring mechanism (2.4).

A large screw clamp and spring are provided to control compression settings. When twisted clockwise, the spiral compresses - the compressor switch-off pressure increases. Reverse adjustment - weakens, and accordingly, the pressure level for shutdown decreases.

It is worth remembering: by increasing the shutdown compression strength, we are changing the factory settings, which were set taking into account the regulatory requirements for the operation of the equipment. Before making adjustments, check the technical documentation of the device so as not to exceed the limits stated by the manufacturer

When reproducing settings, the receiver must be at least 2/3 full.

Having understood the purpose of the elements, let's proceed:

1. To ensure the proper level of safety, we turn off the power supply.
2. Changing the compression level of the springs is done by turning the nut several turns in the required direction. On the board, near the large-diameter adjusting screw, according to the standards, there is a symbol in Latin letters P (Pressure), a smaller one - ΔР.
3. The adjustment process is monitored visually on a pressure gauge.

For convenience, some manufacturers place the adjusting fittings for changing the nominal value on the surface of the device body.

Possible malfunctions of the device

Several malfunctions characteristic of pressure switches are noted. In most cases, they are simply replaced with new devices. However, there are minor problems that you can fix yourself without the help of a repairman.

If the cause of the malfunction was determined to be a pressure switch, the technician will insist on replacing the device. All service actions for cleaning and replacing contacts will cost the user more than purchasing and installing a new device

The most common malfunction is characterized by air leakage from the relay when the receiver is turned on. In this case, the culprit may be the start valve. It is enough to replace the gasket and the problem will be eliminated.

Frequent starting of the compressor indicates loosening and displacement of the adjusting bolts. Here you will need to double-check the threshold for turning on and off the relay and adjust them according to the instructions in the previous section.

Troubleshooting methods

A more difficult problem lies ahead if the compressor does not work. There may be several sources. Let's consider one of them - melting of the pressure switch contacts due to erosion arising from electrical sparks.

Burning of the contact group occurs due to electric spark erosion, which is formed as a result of the opening of the contacts. However, it is not always possible to replace elements - some modifications are no longer available for sale

To eliminate this type of malfunction, you can use one of the following methods: clean the surface, which extends the service life by at least 3 months, or repair it by replacing the contacts in the terminal clamps.

Step-by-step instructions for the second option:

1. Bleed all air from the receiver and turn off the power to the ejector. Remove the pressure switch.
2. Having removed the protective housing, disconnect the wiring connected to the group of contacts.
3. Using a screwdriver, you need to remove the terminal with contacts and drill out the burnt lines from it.
4. You can replace the wire with copper wire. It is necessary to select it taking into account the diameter of the hole, since it must fit tightly into the seat. It is inserted into the hole and pressed on both sides.
5. Similar actions are performed with the remaining burnt lines.
6. After the contact group is assembled, it is mounted in its original place and the pressure switch cover is screwed on.

The compressor relay operates in difficult conditions, subject to wear and failure.

Although the repair is not cost-effective, those familiar with the device can perform the repair themselves. However, the option of replacing it with a new device still remains profitable.

Conclusions and useful video on the topic

Details about the design of the pressure switch, as well as a visual process for adjusting its parameters in the plot:

It is also possible to independently assemble the control unit for the compressor; see this video:

Pneumatic devices are considered safer and easier to use than electric or gasoline models. There is a wide selection of additional equipment that works with compressed air: guns for washing, inflating tires or painting and many others.

With the help of a relay, it becomes possible to operate automatically while maintaining the required compression level in the receiver.

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