Pressure switch: what is it and how does it work

Any gas or liquid medium in a closed container exerts pressure from the inside on the walls of this container. If the pressure force exceeds the strength of the walls, they may collapse and an accident will occur. To prevent this from happening, pressure must be controlled and, if possible, managed. For this, many different devices have been created, including a pressure switch that performs two functions - control and management.

When is a device needed and can it be dispensed with?

The pressure switch should be considered as an element of the automation system for a pump that pumps liquid. Its function is to turn off the pump when the liquid at the control point creates a pressure equal to the prescribed one. And when the pressure drops below the regulated level, the pump turns on. In this way, the water level in the accumulator can be maintained.

You can do without this device in two cases. The first is when the level of liquid in the tank is of no interest to anyone. This is rare, but it does happen. The second case is when the pressure needs to be maintained with high accuracy. Then you will have to install not a relay controller, but a more complex one - electronic or programmable digital.

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The device and principle of operation of the water pressure switch

If we consider the structure of the pressure switch, we can distinguish two components - a sensor (it is also a pressure sensor) and an actuating part (relay output contacts). The whole device is called a "relay" because it has only two states - "output contacts closed" and "output contacts open".

Electromechanical Models

In these models, only the mechanical elements of the device react to changes in the parameters of the fluid (water) flow. A flexible steel plate bends more or less as the water flow rate changes. The plate is connected to two springs that close or open electrical contacts (which is why the relay is called electromechanical). Variable spring rate sets the pump on and off points.

One spring determines the maximum value of water pressure and turns off the pump. The second spring is set to the difference between the upper and lower pressure limits and turns on the pump. Water is pumped into a hydraulic accumulator.

Electronic options

The sensitive element of the device is a strain gauge sensor - a semiconductor element that changes its electrical resistance in accordance with the load. And the load is the water pressure in the pipe or in the accumulator tank. The pressure information is processed by a microprocessor computer. The result of the calculation turns the water pump on or off.

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Which device is better to choose

There are a lot of offers on the instrument market, and the choice for an uninitiated person is difficult. You will have to read the technical literature and consult with experts.

Design and technical parameters

Electromechanical relays are simple in design and reliable in operation. But their accuracy is unstable, it depends on the temperature of the water and the environment.

Electronic pressure switches are the most modern solution to the problem. They have fairly broad functionality, high accuracy, the presence of a liquid crystal display with digital indication of values, ease of setting, wide range of adjustable values ​​and parameters.

Manufacturer

There are many worthy sellers in the plumbing equipment market. It is impossible to list and compare all of them. For example, we offer one of the well-established models.

Aquario Company (Akvario) launches the Hydroprotector 6320 water pressure switch for pumping equipment. This device is used to automatically stop the pump when there is no water in the water supply. The requirements for water are the absolute absence of mechanical impurities and the water temperature is not higher than 500 °C. A special feature is a very easy connection to pumping equipment and no need for adjustment.

Connecting the water pressure switch for the pump

Consider how the water pressure switch is connected correctly - to electricity and to the water supply.

Electrical part

Power is supplied through the cable, which is inserted through the holes in the relay cover. Three terminal blocks are located under the cover: one is used to connect the RD to the pump, the other is designed to connect the power wire (from a 220V socket), the third one is for the ground wire.

Water connection

Using the example of an electromechanical relay, it is convenient to consider the process of connecting a pressure switch to a water supply system. This option is the simplest scheme. It is necessary to prepare a special fitting with five adapters. Two fittings connect the water inlet and outlet to the pipeline, one more fitting connects to the accumulator, and two small diameter outlets are used for the pressure gauge and RD. All outlets are threaded, sealing is carried out with fum tape or tangit unilok thread.

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RD setup

After purchase and installation on site, the pressure switch is not always ready for operation. It is necessary to set the settings corresponding to specific conditions and adjust the device.

Primary adjustment

An initial adjustment of the pressure switch may be required if the factory settings are not suitable for specific conditions. Basically, this refers to the relay thresholds. The basic settings are usually at the level of 1.4-1.5 atm - this is the lower threshold and 2.8-2.9 atm - the upper one.

If any parameter does not correspond to the specific operating conditions of the system, you will have to reconfigure it as required. For example, when installing a jacuzzi, the standard pressure of 2.5–2.9 atm is not enough, it must be increased.

Two springs are installed in the RDM-5 electromechanical water pressure switches, which set the thresholds for turning off or turning on the pump. These springs differ in size and purpose: a large one regulates the relay operation limits (upper - turning off the pump and lower - turning on), and a small one changes the delta - the gap between the upper and lower boundaries pump operation.

To change the parameters, it is necessary to tighten or unscrew the nuts on the springs. If you tighten the nuts, the pressure increases, if you loosen it, it drops. The nuts only need to be turned one turn.

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Re-adjustment

Re-adjustment may be required in different cases. For example, after the elimination of a malfunction or when determining new thresholds.

The threshold for turning on the pump (corresponding to the lower pressure threshold on the water pressure switch) is associated with the pressure in the air part of the accumulator. To increase the service life of the accumulator elements, it is necessary that the minimum pressure in the water supply system be 0.1–0.2 atm higher than in the tank. For example, if the pressure in the tank is 1.4 atm, the shutdown threshold is 1.6 atm. With such ratios of parameters, the tank membrane will last longer. But for the pump to work under normal conditions, the lower pressure threshold must not be higher than the selected value (below or equal). Then the pump will work normally.

By the way, the pressure in the accumulator must be checked before setting. It happens that the declared parameters significantly deviate from the real ones. To correctly determine the value of the response thresholds, it is necessary to control the real values ​​​​with a pressure gauge during the operation of the system.

The upper threshold - turning off the pump - is set automatically during adjustment. The relay in the initial state is set to some kind of pressure difference (delta), usually 1.4–1.6 atm. So, if the inclusion is set, for example, to 1.6 atm, the shutdown threshold will be automatically set to 3.0–3.2 atm (depending on the relay settings). If a higher pressure is needed (to raise water to the second floor, or when the system has many draw-off points), the shutdown threshold can be increased. But at the same time, the parameters of the relay itself will act as restrictions.

The upper limit of the relay operation is fixed and in household models usually does not exceed 4 atm. It just won't work anymore. The upper limit of the pump pressure is also fixed. The pump must be turned off at least 0.2–0.4 atm before the declared characteristic. For example, the upper pressure threshold of the pump is 3.8 atm, the shutdown threshold on the water pressure switch should not be higher than 3.6 atm. But in order for the pump to work for a long time and without overloads, it is better to make a larger difference - overloads have a too bad effect on the operating life.

In practice, during system tuning, the selected parameters are continuously adjusted in one direction or another. The main task is to ensure the normal operation of all water points, including household appliances.

Idle protection

The normal water pump should not turn on and be in a state of operation when there is no water. This will cause it to break. The sales documentation specifically states that it is forbidden to use the pump without water. Such breakdowns are easily diagnosed and are not subject to warranty repairs.

In the wells where the pump operates, a float control and protective device is installed that turns off the pump in the absence of water. Where the float does not fit, a dry-running protection relay is installed. This is the pressure control set by the pump manufacturer and is between 0.4 and 0.6 bar. The user cannot change this value. A stopped pump can only be put into operation manually by filling it with water.

The flow switch will also stop the pump if there is no water. But the market is full of low-quality products, and even the best devices work no more than a year and a half. Experts recommend the simultaneous installation of a float and a pressure switch.

Features of using different pressure levels

Professionals involved in the transportation of water to meet domestic needs, under the term "water pressure" refers to the distance that a water column can be raised above ground level to a point drawdown. This definition is also true for water pumps that lift water from deep. Physicists have several more definitions of the concept of "water pressure". Basically, they differ in the choice of the starting point of reference. The water pressure in the plumbing system is determined by the power of the pump pumping water.

In domestic conditions, water consumption and electricity consumption for its provision are of interest. These values ​​​​depend on the diameter and material of the water pipes, on the temperature of the water.

Possible malfunctions

There are many places in plumbing systems where malfunctions are possible at any time: pipes burst, joints of parts flow, gaps and passages become clogged. Therefore, plumbing equipment must be correctly selected and installed, as well as monitor it.

Conclusion

Plumbing systems are a complex of diverse, interacting equipment. If competent specialists worked at all stages of the creation of the system, then the system will work reliably and will not fail in an extreme situation.