Using an air pneumatic relay allows you to automate the filling of the receiver of the compressor with compressed gas. The equipment operator with the pressostat does not need to monitor the process, trying to fix the limiting parameters. As a result, engine failure is prevented. Significant results, isn't it?
If you plan to purchase a pressure switch for the compressor, then you have come to the right place. It is here that 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. Led options for connecting to the domestic and industrial network with extremely clear diagrams. Dismantled the typical damage and ways to prevent them. The information and useful tips presented by us are supplemented with graphic, photo and video applications.
The content of the article:
- The principle of operation of the pressure switch
- Completion of the compressor automation unit
- Types of pressure control devices
- The structure of the symbols pnevmorele
Air Relay Connection Diagrams
- Option # 1: to the network with a nominal value of 220 V
- Option # 2: to a three-phase network with a voltage of 380 V
- Relay and auxiliary installation
- Adjustment and commissioning process
- Possible device malfunctions
- Troubleshooting methods
- Conclusions and useful video on the topic
The principle of operation of the pressure switch
The name of the relay is determined by its purpose - control of a piston compressor to maintain the required working force of atmospheric pressure in the receiver. Infrequently it can be found on the screw-type device responsible for the compression and air supply.
I take into account the magnitude of the pressure force in pneumatic automation, the device acts on the voltage line, closing or opening it. Thus, an insufficient pressure in the compressor starts the engine, at the time of reaching the required level it switches off.
Such a standard operating principle, based on the connection of a normal closed loop to a circuit, is involved in motor control.
In the design of all ejectors there is a cylinder containing air, in which a certain pressure. Its reduction requires the inclusion of the engine to replenish stock. If the situation is reversed and the excess is fixed - the flow is stopped so that the container does not burst. The pressure switch controls these processes.
Also presented are modifications with the opposite algorithm of operation: reaching the minimum values in the compression scheme, the pressure switch turns off the electric motor, at maximum values it activates. Here the system is operated in a normally open circuit.
The acting system is spring mechanisms with varying degrees of stiffness, reproducing the response to fluctuations in the air pressure unit.
In the course of operation, the indicators formed as a result of the elastic force of tension or compression of the springs and the onslaught of the atmosphere pressed by the device are compared. Any changes automatically activate the spiral action and the relay unit connects or disconnects the power supply line.
However, it should be borne in mind that the device of the review model does not provide for regulatory influence. Exclusively impact on the engine. At the same time, the user has the opportunity to set a peak value, upon reaching which the spring will work.
Completion of the compressor automation unit
The design of the relay is a compact unit, equipped with receiving pipes, a sensing element (spring) and a membrane. The mandatory subassemblies include - unloading valve and mechanical switch.
The sensing assembly of the pressure switch is composed of a spring mechanism, the change of the compression force of which is carried out by a screw. According to the factory standardized settings, the coefficient of elasticity is set at a pressure in the pneumatic chain of 4-6 atm, which is reported in the instructions for the device.
Cheap models of ejectors are not always equipped with relay automatics because such devices are mounted on the receiver. However, during long-term operation, it is reasonable to install a pressure switch to eliminate the problem of overheating of engine elements.
The degree of stiffness and flexibility of the elements of the spring are subject to the temperature indicators of the environment, therefore absolutely all models of industrial devices are designed for stable operation in the environment from -5 to +80 ºC.
The reservoir membrane is connected to a relay switch. In the process of movement, it switches on and off the pressure switch.
The discharge unit is connected to the air supply line, which allows the excess pressure to be released into the atmosphere from the piston section. When this occurs, the unloading of the moving parts of the compressor from excessive effort
The discharge element is located between the ejector check valve and the compression unit. If the motor drive stops working, the unloading section is activated, through which excess pressure is released (up to 2 atm) from the piston section.
With further start or acceleration of the motor creates an onslaught, closing the valve. This prevents drive congestion and simplifies instrument start-up in off mode.
There is a discharge system with a time interval on. The mechanism remains in the open position at the start of the motor for a predetermined period. This range is enough to achieve maximum engine torque.
A mechanical switch is required to start and stop 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 - prevents the accidental start of the motor, even when the pressure in the pneumatic system is low.
Shut-off valves prevent emergencies in the event of failure of control circuit elements, for example, a piston unit failure or a sudden motor stop
Safety in industrial structures should be at a high level. For these purposes, the compressor regulator is equipped with a safety valve. Thus, the system is protected when the relay is operated incorrectly.
In case of emergency situations, when the pressure level is above the permissible norm, and the telepressostat does not work, the safety unit turns on and performs air discharge. According to a similar scheme safety valves in heating systems, the principle of operation and the devices of which are described in the article recommended by us.
Optionally, as an additional protective equipment in the survey device can be used and thermal relay. It is used to monitor the power of the supply current for timely disconnection from the network with increasing parameters.
In order to avoid burnout of the motor windings, the power is turned off. Setting the nominal values is carried out by a special regulating device.
Types of pressure control devices
Variations of the compressor automation unit only two. The determination is made on the basis of their principle of operation. In the first variant, 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 device of the membrane pressure switch: 1 - pressure transducer; 2 and 3 - contacts; 4 - the piston; 5 - spring; 6 - membrane; 7 - threaded connection
Another model with the opposite principle - turns on the engine if pressure drop below the permissible level is determined. Devices of this type are called normally closed.
The structure of the symbols pnevmorele
The labeling of the air pressure switch indicates the entire optional set of devices, design features, including information on the factory settings of the pressure differential.
Condor's production models come with equipment to control pressure in a wide range. The MDR series is aimed at use for ejectors of various power.
Let us examine in more detail the notation using the example of instruments for RDK air ejectors - (*) (****) - (*) / (*):
- RDK - a 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 - performance 18 with switch “switch”; T19P - 19 s;
- (*) - factory settings for threshold operation: 1 - 4... 6 bar; 2 - 6... 8 bar; 3 - 8... 10 bar;
- (*) - discharge valve diameter: 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 - the maximum and minimum, but only downwards.
The specifics of setting the pressure switch for pumping stations are set out in next article, the content of which we advise you to read.
Air Relay Connection Diagrams
Compressor pressostat produced for connection to a variety of load electrical circuits. In accordance with the power line rating, the corresponding model of the relay unit is selected.
Option # 1: to the network with a nominal value of 220 V
If the drive motor is a single-phase device, in this case a 220 V relay with two groups of contacts is installed.
To work with a single-phase load manufacturers recommend equipping the site with the help of models of the RDK series: xT10P-x; xT10K's; 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 circuit load of 380 V, one of the options can be used: a modification of a 220 V or 380 V relay, with three contact lines, to simultaneously disconnect all three phases.
Both methods have different schemes. Consider the first option:
For operation in a three-phase electric circuit, the pressure switch RDK-xT18P-x is used. This model is equipped with three contacts and contributes to the simultaneous switching of all phases.
Having chosen the second method, power is supplied from one phase (zero) and in this case the relay rating should be 220 V. In more detail in the following diagram:
It is allowed to use telepressostatsov of the RDK: xT10P-x, xT10K-x and xT19P-x series with three-phase load, however, the use of such a scheme implies an incomplete disconnection from the mains. More specifically, one phase will be permanently connected to the load.
After connecting to the power supply, it is necessary to understand the additional capabilities presented in the air blocks for the ejectors.
Relay and auxiliary installation
In some versions of the 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 diameter of inch.
By means of several flange connectors, additional elements can be introduced into the system: safety valve, pressure gauge and other necessary mechanisms.
For commissioning the device must be connected to the receiver. Installation consists of the following steps:
- Through the main outlet opening, the device is connected to the compressor.
- A pressure gauge is connected to the device with flanges. There may also be other auxiliary mechanisms that require the inclusion of: safety or discharge valve.
- Channels that are not used for connection, necessarily closed with plugs.
- Further, according to the electrical circuit, the relay is connected to the contacts of the motor control circuit.
Engines with low power can be connected directly; in other cases, additional installation of an electromagnetic starter of the corresponding power is required.
Before proceeding to the settings of the threshold parameters of operation, you should pay attention to the working conditions. First, the adjustment is carried out under pressure. Secondly, the supply of electricity to the engine must be stopped.
Adjustment and commissioning process
Factory set parameters do not always meet customer requirements. In most cases, this is due to insufficient compression force at the highest point of analysis.
The pressure range of the pressure switch may also not be appropriate. In this case, self-adjustment of the actuator will be relevant.
Standard factory settings: upper limit 2.8 atmospheres, lower 1.4 bar. The control of parameters is carried out visually by means of a pressure gauge, which is included in the standard pressostat kit. New models, for example Italtecnica, have a transparent case and are equipped with a compression scale directly on the relay.
To begin setting the working compression value, you will need to inspect a plate with an engraving, where the parameters of the electric motor and compressor are indicated.
We only need the highest value that the device creates. 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 (4.2 atm in the figure), then when all factors are taken into account - differences in power supply, generation the operational life of parts and another - the compressor may not reach the limiting pressure, and accordingly it will not happen shutdown.
In this mode, the working elements of the equipment will begin to overheat, then deform and eventually melt.
The maximum value of the ejector should be taken into account when determining the highest value of the relay. This indicator must be less than the nominal pressure of the compressor. In this case, all elements of the system will work in uninterrupted mode.
For reliable operation without shutdowns, it is required to set the maximum shutdown pressure on the relay that 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 a compressor is turned on / off are regulated by a single bolt. In order not to be mistaken with the choice of direction to increase / decrease on the metal base, the arrows are stamped
Having determined the level to be set, it is necessary to remove the relay case. Below it are two regulating elements - a small and a large nut (in Figure 1.3).
Nearby there are pointer indicators of the direction in which the twisting will be carried out - thereby carrying out the compression and expansion of the spring mechanism (2.4).
Large screw clamp and spring are designed to control compression parameters. When twisting in the clockwise direction, the spiral is compressed - the compressor off pressure increases. Reverse adjustment - weakens, respectively, reduces the level of pressure to turn off.
It is worth remembering: increasing the power of compression off, we change the factory settings, set in accordance with the regulatory requirements for the operation of equipment. Before making adjustments, look in the technical documentation of the device so as not to exceed the limits stated by the manufacturer
When playing the settings, the receiver must be filled no less than 2/3.
Having understood the purpose of the elements, proceed:
- To ensure an adequate level of security, turn off the power supply.
- Changing the level of compression of the springs is performed by turning the nut a few turns in the desired direction. On the board near the adjusting screw of large diameter, by standards, there are symbols of the Latin alphabet P (Pressure), the smaller one - ΔР.
- The control of the correction process is performed visually on the manometer.
Some manufacturers, for convenience, make adjustment valves to change the nominal value on the surface of the device.
Possible device malfunctions
Note several typical pressure malfunctions. In most cases, they are simply being replaced with new devices. However, there are minor problems that you can fix yourself without the help of a master repairman.
If the pressure switch has been identified as a malfunction, the master will insist on replacing the instrument. All service actions for cleaning and replacing contacts will cost the user more than buying and installing a new device
More often than others there is a malfunction characterized by air leakage from the relay when the receiver is turned on. In this case, the culprit may be the starting valve. It is enough to replace the gasket and the problem will be fixed.
Frequent activation of the compressor indicates the loosening and displacement of the adjusting bolts. Here you need to double-check the threshold for switching on and off the relay and adjust them according to the instructions in the previous section.
The solution to a more complex task lies ahead if the compressor does not work. There may be several sources. Consider one of them - the melting of the contacts of the pressure switch due to erosion arising from sparks of electricity.
The burning of the contact group is due to electric spark erosion, which is formed as a result of contact opening. However, it is not always possible to replace items - some modifications are no longer on sale.
To eliminate this kind of malfunction, you can use one of the following methods: clean the surface, that extends the service life of not less than 3 months, or repair, replacing the contacts in the terminal clamps.
Phased briefing of the second option:
- Bleed all the air out of the receiver and turn off the power to the ejector. Remove the pressure switch.
- Removing the protective case, disconnect the wiring to the contact group.
- Using a screwdriver, you must remove the terminal with the contacts and drill out the burnt lines from it.
- Replace the wire can be copper wire. It is necessary to select according to the diameter of the hole, since it should fit tightly into the landing nest. It is inserted into the hole and compressed on both sides.
- Similar actions are done with the rest of the burnt lines.
- After the contact group is assembled, it is assembled in its original place and the cover of the pressure switch is twisted.
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 do it themselves. However, the advantage is still the option of replacing the new device.
Conclusions and useful video on the topic
Details about the device pressostat, as well as a visual process of adjusting its parameters in the plot:
It is possible and self-assembly adjustment unit for the compressor, about this in the video:
Pneumatic devices are considered safer and more convenient to use than electric or gasoline samples. A wide range of optional equipment that works with compressed air is presented: guns for washing, tire inflation or painting and many others.
With the help of the relay, it is possible to automatically work with maintaining the required level of compression in the receiver.
Please write comments in the block form located under the test of the article. Share your own experience in operating a compressor with a pressure switch, ask questions, publish photos on the subject. It is possible that your recommendations will be useful to site visitors.