What is the unloader valve for on the pressure switch?

Hi all! This topic will be of interest to owners of fairly powerful 220 volt compressors and a crappy network...

The more efficient the compressor, the more difficult it is for it to start when the voltage drops. To facilitate starting, powerful compressors are equipped with unloading valves and starting capacitors. If the compressor stops starting, then first of all you should check the inertia switch of the starting capacitor.

It stands on the shaft of the electric motor.

looks something like this

more detailed photo

when the engine does not rotate it closes the contacts of the starting capacitor

If everything is fine, the engine starts easily and naturally!

when the engine spins up to the design speed, the weights begin to move away from the axis of rotation, the pressure disappears and the circuit opens.

Let me tell you, the design is completely unreliable...

The mechanism itself tends to slide to the side, so you have to check it periodically. otherwise the contacts will not press tightly and will burn like in my photo.

And the knot itself is crooked to the point of disgrace. When replacing this contact group, I spent a long time modifying it with a file...

and at the same time I slightly drilled the mounting hole on the shaft. so I hope it doesn’t crawl away)))

BUT for the future there are plans to replace this gravitsap with a time relay and contactor. This will be much more reliable.

The relief valve is a separate issue. Everyone has a basic one. it is located in the pressure switch

If the valve in the pressure switch is working, then after the compressor pumps up the receiver and turns off, a characteristic sneeze is heard, this is the valve releasing pressure from the line.

It is from the line, the thick tube that goes from the head/heads to the receiver, and not from the receiver. Pressure is not released from the receiver thanks to the check valve

2 thick taps are the input of the main line and the output to the receiver, and the thin one is a tap to the pressure switch.

Some compressors are equipped with an additional pressure-type unloader valve. it lets air into the atmosphere up to a certain pressure and then closes.

Thereby allowing the compressor to spin up and reach operating speed.

It is placed in front of the check valve!

I didn’t have it, so to make life easier for the compressor I added it myself.

I didn’t want to cut the tubes, so I had to resort to using a tee and adapters

But at any moment everything can be returned to its original state.

If everything works and the compressor still starts only when the receiver is empty, then you will have to turn on the unloading pre-receiver.

From a 1-2 liter cylinder and insert it into the highway

After the compressor fills the main receiver and the valve in the pressure switch turns off, it releases pressure from the line and from the pre-receiver embedded in it

A small fire extinguisher ala OP-2 is well suited for such purposes.

But there is a better idea!

It’s two in one) At the same time, the air is cooled before entering the receiver)))

To ensure the correct operation of compressor equipment, various technical devices are used, among which is a check valve for the compressor. Without this unit it is almost impossible to imagine the operation of equipment designed for air compression.

Pressure switch for a compressor: independent connection and configuration

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 long-term 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, the pressure switches are additionally equipped with 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.

Check valve

A check valve (return valve) is a device that allows compressed air to flow in only one direction. Structurally, it is assembled (see figure) in a metal case (item 3), inside of which the following are located:

internal shutter (item 6), blocking the inlet;
a spring (pos. 4) pressing the rubber ring (pos. 5) to the bolt seat;
inlet fitting (pos. 7);
plug (item 1) with a sealing gasket made of cardboard (item 2) (the plug makes it possible to disassemble the return for repair or maintenance).

On a note! The check valve has a branch for connecting it to the receiver and a small branch for connecting a pressure switch.

Operating principle

The reverse action valve works as follows. Passing through the outlet valve of the piston cylinder, the compressed air enters the return pipe through the inlet fitting (pos. 7). Having reached a certain pressure, the air lifts the internal shutter (pos. 6) and passes through the cavity in the housing (pos. 3) into the storage tank of the receiver. When the compressor is turned off, the spring (item 4) returns the internal shutter to its place, blocking the path of air from the receiver back into the piston cylinder.

Varieties

On the domestic market you can find compressors with returns made of three different materials: aluminum, plastic and brass. At the same time, the aluminum part differs from its analogues in its high reliability and durability. It is built inside the air duct that connects the piston cylinder to the receiver, and is capable of operating under high temperature conditions (up to 200°C). Whereas a plastic return line is installed in budget models operating at a low temperature of the working environment. As for valves made of brass, they are widely used. Such return valves are quite reliable and perfectly maintain their performance characteristics in cases where the air temperature during compression does not exceed 140°C.

Recommendations for selection

If the compressor return valve fails, it is not difficult to replace it with a similar one

However, before you buy a new valve, you need to pay special attention to the diameter of the threads cut on the outlets of its body. After all, the connecting dimensions of the return, compressor and receiver may differ from each other

Advice! When going for a new check valve for your compressor, do not forget to take the failed part with you. This will greatly facilitate the selection procedure for a new node.

It is also necessary to take into account the technical characteristics and operating conditions of the compressor. After all, there are valves that are not designed to work with high-pressure compressor equipment. In addition, when the working medium heats up to a high temperature during compression, the use of plastic returns is impractical - it is better to purchase a unit in a metal case, which is mounted inside the air duct connecting the compressor and the receiver. It will not be superfluous to purchase a collapsible design - this will allow you to buy the appropriate repair kit in the future and fix the return fault yourself, replacing the failed parts with purchased spare parts.

Making a check valve yourself

In cases where it is not possible to purchase a new check valve to replace a faulty one, you can make it yourself from scrap materials. For this you will need:

female tee;
spring;
2 couplings with external thread, the diameter corresponding to the internal thread of the tee;
a ball whose diameter is larger than the size of the internal hole in the coupling;
a metal plug with an external thread that matches the internal thread on the tee.

The valve is assembled in the following sequence: first, the coupling is screwed into one of the branches of the tee, then a ball is inserted into the tee on the other side, and then the plug is screwed in, pressing the ball with a spring.

There are several practical tips for making a return line.

It is best to take the ball from an old computer mouse - it has a rubberized surface that will fit more tightly to the edges of the hole.
You can also use a regular piece of pipe of suitable diameter as a body. True, in this case you will have to drill a side hole in it, weld another bend and cut threads at all ends.
The spring must press the ball with a certain force and in no case should it be weakened.

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:

A device is connected to the unloading valve of the receiver.
A control pressure gauge is placed. Otherwise, the threaded entry is plugged.
The motor control circuits are connected to the terminal contacts. If the network voltage changes, then the connection should be made through a surge protector ! This is also necessary when the contact power exceeds the indicator for which the engine is designed.
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, with the cover removed, the compression of the springs 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.

Check valve

internal shutter (item 6), blocking the inlet;
a spring (pos. 4) pressing the rubber ring (pos. 5) to the bolt seat;
inlet fitting (pos. 7);
plug (item 1) with a sealing gasket made of cardboard (item 2) (the plug makes it possible to disassemble the return for repair or maintenance).

Operating principle

Varieties

Recommendations for selection

If the compressor return valve fails, it is not difficult to replace it with a similar one

Making a check valve yourself

In cases where it is not possible to purchase a new check valve to replace a faulty one, you can make it yourself from scrap materials. For this you will need:

female tee;
spring;
2 couplings with external thread, the diameter corresponding to the internal thread of the tee;
a ball whose diameter is larger than the size of the internal hole in the coupling;
a metal plug with an external thread that matches the internal thread on the tee.

There are several practical tips for making a return line.

It is best to take the ball from an old computer mouse - it has a rubberized surface that will fit more tightly to the edges of the hole.
You can also use a regular piece of pipe of suitable diameter as a body. True, in this case you will have to drill a side hole in it, weld another bend and cut threads at all ends.
The spring must press the ball with a certain force and in no case should it be weakened.

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.

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.

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.

How to make a check valve with your own hands

There are situations when the air compressor return valve has failed, and for some reason it is not possible to buy a new part. In this case, the part can be made by hand.

On the Internet you can find quite complex methods for manufacturing this unit using lathes, milling machines and other equipment. But there is still a way to make a simple homemade valve from improvised materials. A drawing of this unit is shown below.

To make a return you will need a metal pipe or tee, a spring, a coupling, a metal threaded plug and a ball.

The air check valve is manufactured as follows.

Take a piece of metal tube of the required size and cut internal threads on both sides.
Drill a hole in the side of the tube and weld a tap (with thread). The receiver will be connected to it. You can also try to find a suitable tee. In this case, there will be no need to weld the outlet.
Screw the coupling into one part of the tube (tee), as shown in the drawing.
Place the ball into the body and press it with a spring. The spring should press the ball with sufficient force and not be too loose.
Pressing the spring, tighten the metal plug. At this stage, the production of the return line is completed.

After this unit is ready, its inlet pipe is connected to the cylinder of the unit, and the second to the receiver.