Water pressure switch: connection, adjustment

When organizing a water supply system at home, not only a pump is needed, but also automation to ensure its operation. One of the necessary devices is a water pressure switch. This small device turns on the pump when the pressure in the system drops and turns it off when the threshold is reached. The value of the on and off parameters can be adjusted. About how this device is arranged, how to connect it and how to regulate it – in the article. 

Purpose and device

In order to maintain a constant pressure in the water supply system of a private house, two devices are needed – a hydraulic accumulator and a pressure switch. Both of these devices are connected to the pump through the pipeline – the pressure switch is located in the middle between the pump and the accumulator. Most often it is located in the immediate vicinity of this tank, but some models can be installed on the pump housing (even submersible). Let’s understand the purpose of these devices and how the system works.

A hydraulic accumulator is a container divided by an elastic pear or membrane into two halves. In one, air is under some pressure, in the second, water is pumped. The water pressure in the accumulator and the amount of water that can be pumped there is regulated by the amount of air pumped. The more air, the higher the pressure maintained in the system. But at the same time, less water can be pumped into the tank. Usually it is possible to pump no more than half of the volume into the container. That is, it will be possible to pump no more than 100-40 liters into a hydraulic accumulator with a volume of 50 liters.

For normal operation of household appliances, a range of 1,4 atm – 2,8 atm is required. To support such a framework, a pressure switch is required. It has two operation limits – upper and lower. When the lower limit is reached, the relay starts the pump, it pumps water into the accumulator, and the pressure in it (and in the system) increases. When the pressure in the system reaches the upper limit, the relay turns off the pump.

In a circuit with a hydroaccumulator, for some time water is consumed from the tank. When enough flows out so that the pressure drops to the lower threshold, the pump will turn on. That’s how this system works.

Pressure switch device

This device consists of two parts – electrical and hydraulic. The electrical part is a group of contacts that closes and opens on / off the pump. The hydraulic part is a membrane that exerts pressure on the metal base and springs (large and small) with which the pump on / off pressure can be changed.

The hydraulic outlet is located on the back of the relay. It can be an outlet with an external thread or with a nut like an American. The second option is more convenient during installation – in the first case, you either need to look for an adapter with a union nut of a suitable size or twist the device itself by screwing it onto the thread, and this is not always possible.

The electrical inputs are also located on the back of the case, and the terminal block itself, where the wires are connected, is hidden under the cover.

Types and varieties

There are two types of water pressure switches: mechanical and electronic. Mechanical ones are much cheaper and usually prefer them, while electronic ones are mostly brought to order.

The difference in prices in different stores is more than significant. Although, as usual, when buying cheap copies, there is a risk of running into a fake.

Connecting the water pressure switch

The water pressure switch for the pump is connected immediately to two systems: to electricity and plumbing. It is installed permanently, since there is no need to move the device.

Electrical part

To connect a pressure switch, a dedicated line is not required, but desirable – there are more chances that the device will work longer. A cable with a solid copper core with a cross section of at least 2,5 square meters should go from the shield. mm. It is desirable to install a bunch of automatic + RCD or difavtomat. The parameters are selected according to the current and depend more on the characteristics of the pump, since the water pressure switch consumes very little current. The circuit must have grounding – the combination of water and electricity creates a zone of increased danger.

Cables are brought into special inputs on the back side of the case. There is a terminal block under the cover. It has three pairs of contacts:

• grounding – the corresponding conductors coming from the shield and from the pump are connected;
• terminals line or “line” – for connecting the phase and neutral wires from the shield;
• terminals for similar wires from the pump (usually on the block located above).

The connection is standard – the conductors are stripped of insulation, inserted into the connector, tightened with a clamping bolt. Pulling on the conductor, check whether it is securely clamped. After 30-60 minutes, the bolts can be tightened, as copper is a soft material and the contact may loosen.

Pipe connection

There are different ways to connect a water pressure switch to a plumbing system. The most convenient option is to install a special adapter with all the required outlets – a five-pin fitting. The same system can be assembled from other fittings, just a ready-made version is always better to use.

It is screwed onto a pipe on the back of the case, a hydraulic accumulator is connected to the other outlets, a supply hose from the pump and a line that goes into the house. You can also install a mud sump and a pressure gauge.

A pressure gauge is a necessary thing – to control the pressure in the system, to monitor the settings of the relay. Mud collector is also a necessary device, but it can be installed separately on the pipeline from the pump. There is generally desirable a whole system of filters for water purification.

With this scheme, at a high flow rate, water is supplied directly to the system – bypassing the accumulator. It begins to fill up after all the taps in the house are closed.

Water pressure switch adjustment

Consider the process of adjusting the most popular instance – RDM-5. It is produced by different factories. Adjustment limits vary, as different sizes of water pipes require different pressures. This device leaves the factory with a basic setting. Usually it is 1,4-1,5 atm – the lower threshold and 2,8-2,9 atm – the upper threshold. If some parameter does not suit you, you can reconfigure it as required. Such a procedure is usually necessary when installing a hot tub: a standard pressure of 2,5-2,9 atm is not enough for the desired effect. In most other cases, reconfiguration is not required.

The RDM-5 water pressure switch has two springs that regulate the pump off / on threshold. These springs differ in size and purpose:

• large regulates the limits (immediately upper and lower);
• a small one changes the delta – the gap between the upper and lower borders.

The parameters are changed when tightening or loosening the nuts on the springs. If you tighten the nuts, the pressure increases, if you loosen it, it drops. There is no need to turn the nuts strongly one turn – this is a change of about 0,6-0,8 atm, and this is usually a lot.

How to determine relay thresholds

The threshold for turning on the pump (and the lower pressure threshold on the water pressure switch) are related to the pressure in the air part of the accumulator – the minimum pressure in the system should be 0,1-0,2 atm higher. For example, if the pressure in the tank is 1,4 atm, the shutdown threshold is 1,6 atm. With these parameters, the tank membrane will last longer. But in order for the pump to work under normal conditions, look at its characteristics. It also has a lower pressure threshold. So, it should not be higher than the selected value (below or equal). Based on these three parameters, you select the switching threshold.

By the way, the pressure in the accumulator must be checked before setting – there are significant deviations from the declared parameters. A nipple is hidden under the removable cover (in different models it looks and is located in different places). Through it, you can connect a pressure gauge (you can use a car or the one you have) and see the actual pressure. By the way, it can be adjusted through the same nipple – increase or decrease if necessary.

The upper threshold – pump shutdown – is set automatically during adjustment. The relay in the initial state is set to some kind of pressure difference (delta). This difference is usually 1,4-1,6 atm. So if you set the inclusion, 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 you need a higher pressure (to raise water to the second floor, for example, or the system has many draw-off points), you can increase the shutdown threshold. But there are limitations:

• The parameters of the relay itself. The upper limit 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. This parameter is also fixed and 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 life.

That’s all for choosing the settings of the water pressure switch. In practice, when setting up the system, you have to adjust the selected parameters in one direction or another, because you need to choose everything so that all points of water intake work normally, including household appliances. Therefore, it is often said that the parameters are chosen by the “scientific poke” method.

Setting the water pressure switch for a pump or pumping station

To set up the system, you will need a reliable pressure gauge, the readings of which can be trusted. It is connected to the system near the pressure switch.

The adjustment process consists in twisting two springs: large and small. If you need to raise or lower the lower threshold (turn on the pump), turn the nut on the large spring. If you turn it clockwise, the pressure rises, counter-clockwise – it falls. Turn by a very small value – half a turn or so.

The sequence of actions is as follows:

• The system is started, the pressure gauge monitors at what pressure the pump turned on and turned off.
• Press or release the large spring.
• They turn on and check the parameters (at what pressure it turned on, at what pressure it turned off). Both values ​​are shifted by the same amount.
• If necessary, make adjustments (adjust the large spring again).
• After the lower threshold is set as you want to see it, proceed to adjust the pump shutdown threshold. To do this, press or lower a small spring. Do not turn the nut on it too much – half a turn is usually enough.
• Turn the system back on and look at the results. If everything suits, they stop there.

What else do you need to know about adjusting the water pressure switch? That not all models have the ability to change the delta, so look carefully when buying. There is a pressure switch for the pump in a moisture- and dust-proof housing. They can be placed in a pit, some models can be installed directly on the pump housing if it has such an outlet.

In some water pressure switches there is also an idle (dry) relay, in general this device is in a separate case, but there are also combined ones. Idling protection is necessary so that the pump does not break if suddenly there is no water in the well or well. Some pumps have built-in protection of this type, for others they buy and install relays separately.