Connection of compressors. Parallel connection of compressors

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 prevent 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. The check valve must be installed 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 for greater efficiency (preferably after the muffler). 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.

Piston compressors are used wherever a stationary or mobile source of compressed air is needed. The relay turns off the compressor motor when the pressure in the reservoir reaches a set value, and starts it again if the pressure in the receiver drops below the permissible value. It also releases excess air into the atmosphere.

Principle of operation

The operating principle of the automation unit is simple. The device is mounted on a pipe communicating with the receiver. The spring-diaphragm pressure switch sensor for the compressor continuously measures the pressure. As soon as it drops below the set value, the sensor rod, under the action of a spring, closes the contacts of the compressor relay and the electric motor is connected, pumping air into the tank. After reaching the set pressure, it presses the rod and opens the contacts, turning off the engine. Adjustment of these values ​​is available to the user.
In addition, when the operating pressure limit is reached, the safety valve included in the device is activated, releasing excess air from the compressor into the atmosphere.

Device

All components of the compressor pressure switch are assembled in a compact unit, covered with a plastic or metal case. The product includes:

• Inlet and outlet pipes.
• The sensitive element is a spring and a membrane.
• Stock. Connected to the membrane and placed inside the spring coils.
• Contact Group.
• Adjustment screws.
• Unloading and safety valve.
• Mechanical switch.

The elasticity of the spring, and, consequently, the sensitivity of the sensor, depends on the ambient temperature; most devices are designed to operate in the temperature range from -5 to +70 °C.

The unloading unit is designed to release air from the compressor cylinders after it stops. Thereby:

• its subsequent launch is facilitated;
• wear of piston group parts is reduced;
• the service life of the entire unit is extended.

When the unloading valve is activated in the silence that follows after the compressor stops, a sharp characteristic sound is clearly audible.

The mechanical switch serves for the initial start and final stop of the compressor. It has two positions: “On” and “Off”. “On” activates automatic operation systems. It transfers further control of the compressor to the pressure switch. The “Disabled” position prevents spontaneous starting of the motor when the pressure in the receiver drops below the set value.

The safety valve allows you to release excess pressure into the atmosphere in the event of a relay failure and avoid compressor breakdown in this case.

A thermal relay can serve as additional protection for the compressor motor. It is included in the automation unit; it disconnects the motor windings from the supply voltage in the event of an increase in current strength, indicating an overload of the motor.

Setting up an air compressor comes down to setting the operating pressure with an adjusting screw. The pressure regulator has values ​​marked on it. Pressure can be controlled more accurately using a pressure gauge.

Types of pressure switch devices

There are two main versions of the device available. The pneumatic-mechanical part is identical; the difference is determined by the method of closing the contacts when the rod moves:

• Normally closed (NC). used for direct control of low and medium power motor circuits.
• Normally open (NO). The movement of the rod closes the contacts when the maximum pressure is reached. The reverse movement opens them as it decreases. The contacts are used to control a more powerful relay that starts and stops the electric motor. The circuit turns out to be more complex, but the load on the pressure switch contacts is reduced and the service life increases.

When replacing a relay, you need to carefully check that its type matches electrical diagram compressor. his type.

Installation of relays and auxiliary elements

In addition to basic components, devices are often equipped with additional devices that increase ease of use or expand the functionality of the device.

They are installed on flange connections, most often 1/4”

The pressure switch is connected to the compressor as follows:

• Screw the inlet pipe to the tank pipe.
• Connect a pressure gauge, unloading and safety valves to the flanges of the device.
• Close unused holes with plugs.
• Connect the electrical connector of the relay to the electric motor.

Low-power electric motors are connected directly; more powerful ones will require the use of a starter. The design of the pressure switch must match the engine power.

Adjustment and commissioning process

The device is configured and adjusted at the manufacturer's factory. Typical values ​​are 2.8 atm. for the upper limit and 1.4 for the lower limit. However, sometimes situations arise in which it is necessary to adjust the device yourself:

• Setting up after partial or complete repair.
• Specific requirements of consumer devices.
• Installing a relay that was not originally designed to work with this compressor.

Before you begin adjustment, you should carefully study the parameters of all mating devices according to their data sheets. Passport data must correspond to the numbers embossed or engraved on a plate attached to the body of the unit.

The main indicator is the maximum pressure for which the compressor is designed. The value at which the pressure switch will operate should be 0.4-0.5 atm less than this maximum. In real operating conditions of the device, taking into account voltage instability, losses in seals, and the degree of wear of the piston group, this pressure may not be achieved. Then the pressure switch will not turn off the motor, the compressor will work continuously, overheat and wear out.

Having decided on the parameter values, you can begin making adjustments. To do this you need:

• Remove the casing.
• Two nuts will become available - a larger one and a smaller one. These are the regulatory bodies. Arrows are engraved on the body nearby, showing the direction of rotation to increase and decrease the parameter, respectively.
• The large nut sets the value at which the electric motor turns off. When rotated clockwise, the value increases, in the opposite direction it decreases. It is indicated by the P (Pressure) icon.
• The smaller nut sets the difference in engine start pressure compared to the shutdown value. It is designated ΔР.

Before you start setting up, you should fill the tank at least 2/3 full. The sequence of actions is as follows:

• Disconnect the unit from the network.
• Adjust the P and ΔP values ​​by rotating the adjusting nuts.
• The set values ​​should be monitored using a pressure gauge.

A number of manufacturers place adjustment controls on the outside of the device. This increases the convenience of adjustment, but at the same time increases the risk of changing the settings by accidental touch.

Possible malfunctions of the device

The device is characterized by its simple design and high reliability. However, they are also subject to malfunctions and breakdowns. A number of minor difficulties can be easily corrected with your own hands:

• Air leakage from the device when the pump is turned on. Identified by a characteristic whistle and the feeling of a sharp cold draft near the body. Most often the cause is a broken start valve. To repair, the gasket must be replaced.
• Frequent starting of the motor. The cause may be loose adjustment screws. It is necessary to carry out the procedure for adjusting the on and off threshold values ​​using the pressure gauge and, if necessary, restore the passport values.

In case of serious problems experienced craftsmen It is recommended not to bother with repairs and subsequent adjustments, but to immediately replace the entire device.

Troubleshooting methods

More complex work will be required if the compressor does not turn on. This can happen if the relay contacts wear out and melt from sparks that occur when the electric current is interrupted. Two methods are possible:

• In case of slight wear of the contact groups, clean the areas with a file or sandpaper. Care must be taken not to bend the slats. This will extend the service life by several weeks.
• Replace the contact groups with new ones from the repair kit for this model.

To repair contact groups, the following operations should be performed:

• Bleed the air from the tank and disconnect the unit from the network.
• Remove the relay from the compressor.
• Remove the casing.
• Disconnect the wires going to the contacts.
• Using a screwdriver, pry the contact terminal out of the mount and carefully drill out the melted areas.
• The wire is replaced with copper wire of the appropriate cross-section. It should fit into the hole with minimal clearance. The wire is passed into the hole and pressed tightly with pliers.
• After repairing all melted contacts, reassemble the device in the reverse order.

It makes sense to spend time on such repairs only if branded spare parts are unavailable for replacement.

The connection diagram for the pressure switch depends on the type of electric motor. Single-phase ones are controlled by relays designed for 220 V with two contact groups. For three-phase electric motors, a 380 V device is installed, with three contact groups, each connecting its own phase. The use of single-phase switches for three-phase loads is unacceptable, since one of the phases remains permanently connected to the winding.

Flange connections

A number of manufacturers install additional flange connectors on their products. Most often there are two or three of them, the standard size is ¼ “. Through them, components such as a safety valve, pressure gauge, etc. are connected.

Installing a pressure switch

For installation, you must perform the following operations:

• Connect the relay to the receiver pipe.
• Connect the pressure gauge, safety and relief valves through the flange connectors.
• Place plugs in the remaining unoccupied connectors.
• Connect the wires from the engine to the electrical connector of the device.
• Make adjustments.

The last point should be considered in more detail.

Important! The adjustment is carried out with at least 2/3 of the tank filled and the power turned off.

The manufacturer supplies devices that have been tested and adjusted to standard values.
If the parameters of a given compressor or the characteristics of consumer devices require you to configure the relay to other values, you should do the following:

• Remove the device cover.
• Two wrench heads will become visible.
• The big one controls the shutdown pressure and is designated by the letter P (Pressure).
• The small one controls the pressure difference at which the motor turns on. It is designated by the letters ΔP.
• The arrows indicate the direction of rotation for increasing values ​​(+) and decreasing values ​​(-).
• Control the pressure using the pressure gauge and set the required values.

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. It is here that you will find an extensive volume of extremely useful information about the principles of operation of the device, its configuration and connection methods.

We have described in detail existing species pneumatic relay. 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 we provide and useful tips supplemented with graphic, photo and video applications.

The name of the relay is determined by its purpose - controlling a piston compressor to maintain the required work force atmospheric pressure. 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: reaching minimum values in the compression circuit, the pressure switch turns off the electric motor, and at maximum, 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 temperature indicators 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 check valve ejector and compression unit. 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 high level. For these purposes, the compressor regulator is equipped with a safety valve. This ensures system protection in case of incorrect relay operation.

At 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. A similar scheme is used in heating systems, the operating principles and devices of which are described in the article we recommend.

Optional as extra protective equipment and can be used in the review device. 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 option, the mechanism turns off the electric motor when the established pressure level limits are exceeded air mass in the pneumatic network. 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 downward.

The specifics of setting up pressure switches for pumping stations are outlined in 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 deal with additional features, presented in 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 basically 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 it is necessary additional installation electromagnetic starter of appropriate power.

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 compressive force in the highest point parsing.

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 indicator scale 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 highest value relay. 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 shutdown 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 any adjustments, please check technical documentation 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 per necessary side. 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.

Please write comments in the block form located under the article test. Share own experience in operation of a compressor with a pressure switch, ask questions, post photos on the topic. It is possible that your recommendations will be useful to site visitors.

Connecting a magnetic starter and its small-sized variants is not difficult for experienced electricians, but for beginners it may be a task that requires some thought.

A magnetic starter is a switching device for remote control high power load.
In practice, often, the main application of contactors and magnetic starters is the starting and stopping of asynchronous electric motors, their control and reversal of engine speed.

But such devices also find their use in working with other loads, such as compressors, pumps, heating and lighting devices.

For special safety requirements ( high humidity indoors) it is possible to use a starter with a 24 (12) volt coil. And the supply voltage of electrical equipment can be high, for example 380 volts and high current.

In addition to the immediate task of switching and controlling loads with high current, another important feature is the ability to automatically “turn off” the equipment when there is a “loss” of electricity.
A good example. While some machine, such as a sawing machine, was operating, the voltage in the network was lost. The engine stopped. The worker climbed to the working part of the machine, and then the tension appeared again. If the machine was controlled simply by a switch, the engine would immediately turn on, resulting in injury. When controlling the machine's electric motor using a magnetic starter, the machine will not turn on until the "Start" button is pressed.

Magnetic starter connection diagrams

Standard scheme. It is used in cases where it is necessary to carry out normal starting of an electric motor. The "Start" button was pressed - the engine turned on, the "Stop" button was pressed - the engine turned off. Instead of a motor, there can be any load connected to the contacts, for example a powerful heater.

In this circuit, the power section is powered by a three-phase alternating voltage of 380V with phases “A” “B” “C”. In cases of single-phase voltage, only two terminals are used.

The power part includes: a three-pole circuit breaker QF1, three pairs of power contacts of a magnetic starter 1L1-2T1, 3L2-4T2, 5L3-6T3 and a three-phase asynchronous electric motor M.

The control circuit receives power from phase “A”.
The control circuit diagram includes the SB1 “Stop” button, the SB2 “Start” button, the magnetic starter coil KM1 and its auxiliary contact 13NO-14NO, connected in parallel to the “Start” button.

When the QF1 machine is turned on, phases “A”, “B”, “C” go to the upper contacts of the magnetic starter 1L1, 3L2, 5L3 and are on duty there. Phase “A”, which supplies the control circuits, comes through the “Stop” button to the “3” contact of the “Start” button, the auxiliary contact of the starter 13NO and also remains on duty on these two contacts.

note. Depending on the voltage rating of the coil itself and the supply voltage used, there will be a different coil connection diagram.
For example, if the coil of a magnetic starter is 220 volts, one of its terminals is connected to the neutral, and the other, through buttons, to one of the phases.

If the coil rating is 380 volts, one output is to one of the phases, and the second, through a chain of buttons, to the other phase.
There are also 12, 24, 36, 42, 110 volt coils, so before you apply voltage to the coil, you must know exactly its rated operating voltage.

When you press the “Start” button, phase “A” hits the coil of the KM1 starter, the starter is triggered and all its contacts are closed. Voltage appears at the lower power contacts 2T1, 4T2, 6T3 and from them goes to the electric motor. The engine starts to rotate.

You can release the “Start” button and the engine will not turn off, since self-retaining is implemented using the auxiliary contact of the starter 13NO-14NO, connected in parallel to the “Start” button.

It turns out that after releasing the “Start” button, the phase continues to flow to the coil of the magnetic starter, but through its 13NO-14NO pair.

If there is no self-retaining, it will be necessary to keep the “Start” button pressed all the time so that the electric motor or other load runs.

To turn off the electric motor or other load, just press the “Stop” button: the circuit will break and the control voltage will stop flowing to the starter coil, the return spring will return the core with the power contacts to its original position, the power contacts will open and disconnect the electric motor from the mains voltage.

What does the installation (practical) diagram for connecting a magnetic starter look like?

In order not to pull an extra wire to the “Start” button, you can place a jumper between the coil output and one of the nearest auxiliary contacts, in in this case these are “A2” and “14NO”. And from the opposite auxiliary contact the wire runs directly to the “3” contact of the “Start” button.

How to connect a magnetic starter in a single-phase network

Electric motor connection diagram with thermal relay and circuit breaker

How to choose a circuit breaker (circuit breaker) to protect the circuit?

First of all, we choose how many “poles”; in a three-phase power supply circuit, a three-pole circuit breaker will naturally be needed, and in a 220 volt network, as a rule, a two-pole circuit breaker will be sufficient, although a single-pole circuit breaker will be sufficient.

The next important parameter will be the operating current.

For example, if the electric motor is 1.5 kW. then its maximum operating current is 3A (real operating current may be less, it must be measured). This means that the three-pole circuit breaker must be set to 3 or 4A.

But we know that the starting current of the engine is much higher than the operating current, which means that a regular (household) automatic machine with a current of 3A will operate immediately when starting such an engine.

The characteristic of the thermal release must be selected D so that the machine does not trip when starting.

Or, if such a machine is not easy to find, you can select the current of the machine so that it is 10-20% greater than the operating current of the electric motor.

You can also go into a practical experiment and use a clamp meter to measure the starting and operating current of a particular motor.

For example, for a 4kW motor, you can install a 10A automatic.

To protect against motor overload, when the current increases above the set value (for example, phase loss), the contacts of the thermal relay RT1 open and the power circuit of the electromagnetic starter coil is broken.

In this case, the thermal relay acts as a “Stop” button, and is in the same circuit, in series. Where to put it is not particularly important, it can be in the section of the L1 - 1 circuit, if it is convenient for installation.

With the use of a thermal release, there is no need to so carefully select the current of the input circuit breaker, since the thermal protection of the motor should be quite adequate.

Connecting an electric motor via a reversing starter

This need arises when it is necessary for the engine to rotate alternately in both directions.

Changing the direction of rotation is implemented in a simple way; any two phases are swapped.

In most cases, inexpensive models of air compressors are not equipped with a pressure switch, since such products are mounted on the receiver. Based on this, many manufacturers think that visual monitoring of pressure using a pressure gauge will be more than sufficient. However, during prolonged operation of the device, if you do not want to cause the engine to overheat, it makes sense to install a pressure switch for the compressor! With this approach, the drive will be turned off and started automatically.

Circuit and device

The device is divided into the following types:

• Starting the electric motor of the compressor when the pressure drops below the set value (normally closed);
• Switching off the engine when the air pressure rises above the normal level (normally open).

The executive element in the device is springs. Their compression force is measured using a special screw. As a rule, manufacturers adjust the compression force of the springs so that the pressure in the pneumatic network is in the region of 4-6 at. This parameter is always precisely indicated in the instructions.

Since the flexibility and stiffness of springs always largely depends on temperature, all elements of industrial pressure switches are designed and created taking into account subsequent operation at temperatures from minus 5 to plus 80 degrees.

The pressure switch includes 2 mandatory subassemblies in its design - a mechanical switch and a relief valve. A mechanical switch protects against accidental starting of the engine, thus performing the stand by function. After pressing, the device drive starts, after which the compressor begins to operate in automatic mode. Without pressing the button, the electric motor will not work even with reduced pressure in the pneumatic network.

The unloading valve is connected to the air supply line between the compressor and the receiver and is responsible for engine operation. When the compressor drive is turned off, the unloader valve on the receiver gets rid of excess compressed air, thus relieving the moving parts of the extra effort required when restarting the compressor. This eliminates overloading of the engine during torque. When the unloaded engine is turned on, the valve closes, which prevents unnecessary load from being created.

For greater safety, pressure switches are equipped additionally safety valves, which turn out to be very useful, for example, in case of piston failure, sudden stop of the electric motor and in any other emergency situation!

A thermal relay can also be installed in the pressure switch housing, allowing you to monitor the current strength in the primary circuit. When this parameter is increased, the thermal relay will automatically turn off the engine, thus protecting the device from overheating and breakdown of the windings.

Connecting and setting up a pressure switch

The pressure switch in the compressor installation circuit is located between the secondary engine control circuit and the unloader valve. As a rule, a pressure switch for a compressor is equipped with 4 threaded heads, one of which is intended for connecting the control pressure gauge, the second for connecting the device to the receiver. A ¼-inch threaded plug is installed on one of the remaining ones, and a safety valve is installed on the last one. The presence of a free connector makes it possible to place the control pressure gauge in the most convenient place.

The pressure switch is connected in the following order:

1. A device is connected to the unloading valve of the receiver.
2. A control pressure gauge is placed. Otherwise, the threaded entry is plugged.
3. The motor control circuits are connected to the terminal contacts. If the network voltage changes, then the connection should be made through network filter ! This is also necessary when the contact power exceeds the indicator for which the engine is designed.
4. The compressed air pressure readings can be adjusted if necessary using adjusting screws.

Before connecting the pressure switch to the compressor, it is worth checking that the network voltage corresponds to what is specified by the manufacturer! For example, a two-contact group is used for a three-phase network with a voltage of 220V, a three-contact group is used for a voltage of 380V.

The setup is performed with the receiver at least 2/3 full. To do this, the relay is disconnected from the power supply, after which, when removed cover, spring compression is adjusted. The maximum operating pressure is determined by the adjusting screw with the axis of the larger spring. The second adjusting screw, with a smaller spring, allows you to adjust the pressure difference. In most cases, the manufacturer indicates on the board the direction of rotation for increasing and decreasing pressure. Here you can also see the generally accepted designation for pressure - the Latin letter “P” and “ΔP”.

In some models, to reduce the time required to adjust the pressure, the manufacturer places the adjusting screw outside the pressure switch housing. In this case, the result is controlled based on the pressure gauge readings.

DIY pressure switch

If you have a working thermostat at home from an old refrigerator, as well as some operating skills, then you can easily make a pressure switch for the compressor with your own hands. However, it is worth warning in advance that such a solution will not have great practical possibilities, since the upper pressure with such an approach will be limited only by the strength of the rubber bellows.

It is most convenient to convert the KTS 011 thermal relay into a pressure switch, because they differ in the reverse operating sequence - when the temperature in the chamber decreases, they turn off, and when the temperature in the chamber increases, they turn on.

Work order

After opening the cover, the location of the required group of contacts is determined, and for this purpose the circuit is ringed. The first step is to modify the connection of the compressor with the thermal relay: the contact groups are connected to the terminals of the electric motor circuit, and the unloading valve is connected to the outlet pipe with a control pressure gauge. The adjusting screw is located under the thermal relay cover.

When the compressor starts, the screw rotates smoothly, at the same time you need to monitor the pressure gauge readings. It is worth making sure that the receiver is 10-15 percent full! To achieve minimum pressure, it is necessary to smoothly move the face button rod. For this purpose, the cover is placed in its original place, after which the adjustment is performed almost blindly, since there is nowhere to install the second pressure gauge.

For safety reasons, it is not recommended to set the thermostat pressure beyond 1-6 atm! If you use devices with a stronger bellows, the maximum range can be raised to 8-10 at, which is usually enough for most tasks.

The capillary tube is cut only after you are sure that the relay is working. After releasing the refrigerant inside, the end of the tube is placed inside the relief valve and sealed.

The next step is to connect a homemade pressure switch for the compressor to the control circuit. To do this, the relay is fixed to the control board with a nut. The locknut is screwed onto the thread on the rod, thanks to it you can subsequently adjust the air pressure.

Taking into account the fact that the contact group of a thermal relay from any refrigerator is designed to work with high currents, they can switch fairly powerful circuits, for example, secondary circuits when working with a compressor motor.