Pressure switch for a hydraulic accumulator: connection, setting, adjustment

Recommendation points

• How does a water pressure switch work
• Varieties and selection rules
• Installation on a pumping station
• Electrical connection options
• Adjustment and possible malfunctions

Automation of pumping stations is most often performed using one simple device – a water pressure switch. In today’s article we will talk about the intricacies of the selection, installation and electrical connection of this most important unit of the plumbing system..

How does a water pressure switch work

Mechanical pressure switches have a very simple design. A threaded branch pipe for connection to a water supply system is directly connected to a small chamber in which a movable piston with a rod is installed. The piston lift height directly depends on the current pressure in the system.

Water pressure switch device: 1 – cover; 2 – case; 3 – cable glands; 4 – branch pipe for connection to the water supply system; 5 – terminals for grounding; 6 – terminals for electrical connections; 7 – nut for adjusting the pressure difference; 8 – nut of shutdown pressure adjustment

The relay operates in a certain range between the minimum and maximum working pressure, the limits are set by the force of the adjusting springs. A drop in pressure in the water supply system is the only sign by which the automation can understand that one of the water outlets is open and the system needs to be recharged.

Therefore, when the pressure drops below the minimum mark, when the spring force is higher than the piston resistance, the mechanics closes the pump supply circuit and turns it on. When the pressure in the system, transmitted through the movable rod, becomes equal to the spring force, the mechanism discards the contact group and the pump is turned off.

How the pressure switch works

The electrical contacts that switch the power circuit are connected to the regulating springs by an intricate mechanism. To eliminate breakdown from the power supply circuit, part of the mechanism is made with dielectric materials. The contact block and mechanics are hidden inside the case, the user can only access a series of screw terminals for connecting wires.

Varieties and selection rules

In plumbing stores, mechanical water pressure switches are presented in a really large assortment. They rarely have fundamental differences in the device, but may differ in a number of other parameters..

1. Working pressure range.
2. Permissible current load on the contact group.
3. Dry run protection.
4. The presence of a built-in pressure gauge to control the current pressure.
5. Overall quality of workmanship of parts, which determines the reliability of the device.

When choosing a device for your plumbing system, you need to rely on the design pressure values ​​and technical parameters of the pump. For example, it makes no sense to purchase a relay with the upper limit of the range of 8 kgf / cm², if the pump is capable of delivering only 5 kgf / cm².

Of course, both the length of the supply line and the installation depth of the pump must be taken into account. Very often, the passport data of the pumping equipment have significant differences from the real operating parameters of the system and the pressure at the place of installation of the relay. The probability of error is especially high when using a submersible pump with the placement of a hydraulic accumulator and automation on the surface..

Dry year protection is a very important function. The presence of an airlock either indicates a drop in the water level in the well / well or a dirty suction port, or it is a sign of a general malfunction of the plumbing system. In any case, turning on the pump in this mode is almost guaranteed to lead to its breakdown..

Installation on a pumping station

Although the pressure switch can be installed almost anywhere in the system, it is recommended to place it in the general complex of the pumping station equipment. The most preferable place of installation is an additional branch of the technical manifold or a cross connected to the main branch of the accumulator. At this point in the system, inertial pressure surges are expressed to the smallest extent, which guarantees the lowest probability of malfunction..

There are also a number of basic requirements for the point of water injection into the system:

1. The relay should be installed behind a check valve that blocks the water injected into the system and maintains static pressure in the system after the pump is turned off.
2. Since the relay mechanics are quite thin, a simple mud filter should be installed in front of the collector into which the tie-in is made.
3. For convenient adjustment, a control pressure gauge and a water intake point with shut-off valves must be installed in the immediate vicinity of the relay.

1 – borehole pump; 2 – check valve; 3 – pumping station; 4 – manometer; 5 – pressure switch; 6 – mechanical cleaning filter; 7 – pump control automation; 8 – well caisson

Two types of connections can be provided for connecting the relay to the manifold. The most common version is with a quarter-inch flare nut. Such a connection does not require additional sealing, a standard PTFE gland will be quite enough.

A different connection option is more typical for relays with high operating pressure parameters. The relay has a half to full inch male thread. The installation should be carried out with sealing the threaded connection with Teflon FUM tape or thread, having previously counted the number of turns.

Electrical connection options

In the standard configuration of the device, the terminals for connection are arranged in pairs: phase and zero of the supply network and parallel contacts for connecting a cable or pump wire. The relay opens both contacts, the phasing of the connection can be any.

The contacts of the terminal block are usually located in two horizontal rows: the lower one is supplied with power, from the upper one the switched network of the pump is removed. Optionally, there is a bolt on the metal case or a third pair of contacts on the terminal block for connecting ground.

The inclusion of an intermediate contactor in the circuit is typical when connecting high-power pumping equipment, if the load on the contact group exceeds the established norm (10 or 16 A). It is also possible when working with three-phase pumping equipment, because relays rarely have three pairs of switched contacts. If you doubt the location and principle of operation of the contacts, and the instructions for the device do not clarify, activate the mechanism manually and perform a continuity of the terminal block.

Adjustment and possible malfunctions

All relays have factory set pressure limits, which do not always correspond to the optimal parameters for a particular plumbing system. The relays can and should be adjusted after installation, for which two springs with nuts are provided.

The smaller spring defines the operating range – the difference between the on or off threshold. A large spring serves to displace the working range: if the nut is tightened, the displacement occurs to the higher side and vice versa.

The relays are adjusted on the fly: first, by tightening the larger spring, the shutdown threshold is raised to the desired level. The pump will periodically turn on for priming, when the pressure gauge shows the required value, the threshold setting can be considered complete.

After that, you need to open the water intake and wait for the pump to turn on, noting the readings of the pressure gauge at this moment. Periodically tightening or releasing the nut and draining the water from the system, it is necessary to achieve the correct value of the lower limit of the range – the switching threshold.

If a pressure reducer is used in the system, the switch must have a switch-on setting approximately 0.7–1 bar higher than the water pressure leaving the reducer. You must also take into account the permissible pressure for other system components and, in particular, the accumulator..

During operation, typical failures in the operation of the relay can be observed:

1. The relay does not turn off – the pump cannot create the required pressure or the range is too high.
2. The relay works in intermittent mode when the water intake is open – too narrow range or faulty accumulator.
3. The relay does not turn on the pump – mechanical failure or wire breakage.
4. The adjustment changes spontaneously – the relay is in the vibration zone, due to which the nuts are released by themselves, they need to be counterbalanced.