How to correctly measure the water pressure in the tap

Now produced a lot of household appliances that can make life easier and create comfortable conditions. Some household appliances require connection to water supply systems.

Tap water

For the correct connection of various plumbing devices you need to know the water pressure in the faucet.

Knowing how to measure the pressure of water in the faucet will help to avoid unpleasant surprises in the future associated with improper operation of the devices due to insufficient network pressure.

For the normal operation of water-consuming appliances, it is necessary that the value of the water pressure in the pipeline correspond to the passport data specified in the operating documentation.

So, approximately these values ​​are:

  • washing machine - 2 bar (approximately 2 atm (physical atmosphere) or 2 kgf / cm² (technical atmosphere));
  • hot-water column and dishwasher - 1,5 bar;
  • hydromassage and shower facilities - 4 bar.

According to the requirements of regulatory documentation, fluctuations in the pressure in residential buildings can be from 0.3 to 6 kgf / cm², which in theory can lead to malfunctions in the operation of devices connected to water mains.

Measurement of pressure

The scheme of a stationary manometer

The scheme of a stationary manometer.

Measuring the pressure in the pipeline is very simple, if at any stage of repair or even during the construction of the house at the entrance to the apartment on the water line, a pressure gauge was installed - a manometer. In this case, it's enough just to look at his scale.

Ideally, gauges should be installed in front of each water user critical to the water supply mode. This is due to the fact that the internal layout of the apartment has a lot of places that reduce the pressure of water.

From this point of view, the critical places of the internal water supply system are:

  • areas of variation in the cross-section of pipes
  • insertion of shut-off and control valves;
  • main filters;
  • turns and tees.

However, in practice, most often, if the pressure gauge is on an in-house water pipe, it is somewhere in the area of ​​the valve that cuts the apartment from the central riser of the water supply.

Indications of such a pressure gauge will not take into account all intra-apartment pressure losses. Therefore, they can be taken into account with some assumption.

Portable manometer

Another, more universal method of measurement involves the production of measurements of the characteristic of interest directly at the point of operation.

The scheme of a portable manometer

The scheme of a portable manometer.

To implement this method you need:

  • a manometer whose scale makes it possible to make measurements in the range of values ​​typical for apartment water supply;
  • thread extender;
  • set of adapters for metric and inch threads for connection of a manometer to the control point;
  • фторопластовая лента ФУМ.

The measurement of the water pressure in the network can be carried out at any point of interest. To carry out the experiment, it is necessary to connect the manometer to the water supply network.

The selected connection is depressurized:

  • a flexible hose to the kitchen faucet;
  • The supply hose to the washing machine or dishwasher;
  • подводка к баталю unitaza;
  • shower mixer;
  • main filter housing.

If necessary, you can even disassemble any of the internal water pipe connections or cut directly into the pipe a tee with a manometer. The variant with a sidebar of a constant manometer will allow you not to puzzle over how to measure the pressure.

If the water pipe is depressurized, remember to close the water supply valve to the apartment.

Pressure switch circuit

The scheme of the pressure switch.

For the convenience of connection, the thread extension and the adapter required for connection to the trunk are screwed onto the inlet thread on the manometer body. The resulting design is installed at the selected connection point.

Sometimes there is a situation where you can not find the appropriate adapters. Correct position will help the use of a rubber hose, which will be worn on the pressure gauge and the measured point. Sealing and additional fixing of the connection in this case can be ensured by means of a pair of clamps.

To facilitate their own lives, excluding water spills and their inevitable elimination, all threaded parts of the joints are further sealed. Several turns of FUM tape will reliably hold all the water inside the system.

After connecting the manometer, the water pressure is switched on and the required value is measured.


One of the most universal methods of measuring water pressure is the use of a manometer.

Most often, all manipulations with the connection of measuring equipment are carried out on a mixer in the bathroom.

This is understandable:

  • in the bathroom there is enough convenient access to plumbing fixtures;
  • when connecting a manometer, there is no need to block the flow of water into the apartment - it is enough to close the faucets on the mixer;
  • In case of loose sealing of internal connections, water will spill into the bathroom.

When assembling the entire measuring structure, some amount of air inevitably remains in the pipeline between the pressure gauge membrane and the shut-off valve. In order to more accurately measure the water pressure, it is necessary to firstly vent it.

The scheme of connection of a tube to a manometer

Scheme of connection of the tube to the manometer.

Completely air can be removed if a special tap is installed in front of the measuring device.

But since the pressure measurement is occasional and the residual quantity does not introduce fatal errors into the result, the air effect can be neglected.

It will be enough to open a nearby tap and drain some water from the pipeline. The remaining air leaves most often with this water.

In the case of measuring the pressure in the shower mixer is still easier. It is enough to switch the water pressure regulator of the shower-cock several times.

Calculation-experimental methods

Determination of the network head is possible not only with the help of specialized instruments, but also using self-made devices and hydrodynamic calculation formulas. An example of calculation and experimental methods can be the determination of pressure by means of a hose and the calculation method through the flow of water.

Scheme of the water pressure regulator

Scheme of the water pressure regulator.

In other words, a hydraulic calculation of the existing system must be carried out with sufficiently large assumptions that allow to omit:

  • hydrodynamic resistance of individual sections of the pipeline;
  • the flow regime of the liquid inside the pipe;
  • material and length of the pipeline.

The results of such calculations and experiments are likely to differ by a significant error and have a qualitative (reference) character.

Measurement of pressure

Tentatively, you can calculate the water pressure in the tap using a simple device made from any transparent hose. The approximate length of the hose should be 2 m.

The hose is mainly used to measure the pressure at the outlet of the tap. To carry out the measuring process, the hose must be connected at one end to the crane in question. Then carry out a brief start of the water.

Before proceeding to the main part of the experiment, two conditions must be fulfilled:

  • The hose is installed vertically and its free end is plugged with a suitable stopper;
  • an important point here is the installation of the hose in such a way that the water level in it coincides horizontally with the level of the outlet location from the tap (zero level).
Scheme of measuring water pressure hose

Scheme of measuring the water pressure with a hose.

Once all the conditions are met, you must turn on the water by fully opening the tap. After a short time in the hose a new constant level will be established.

In the steady state, two values ​​must be fixed:

  • the length of the hose from the zero level to the plug;
  • the length of the hose piece between the new, steady level of water and the plug.

The approximate value of the water pressure can be determined by calculation using the formula:

R = Ratm × N0 / H1, where:

  • P is the pressure in the system, atm;
  • Ratm - atmospheric pressure present in the tube before the opening of the crane (1 atm);
  • H0 is the height of the air column in the hose prior to the start of the experiment;
  • H1 - the height of the column of air in the hose under steady-state conditions after water supply.

It should be noted that the assembled unit is a liquid manometer according to the principle of operation. The principles of its use and connection will be the same as in the case of using the usual manometer described above.

The main disadvantages of this method will be:

  • the need for reliable sealing of the open end of the hose and the location of its connection to the network;
  • the need to provide a vertical position of the measuring hose, which at a length of about 2 m can be very difficult;
  • all assumptions that are characteristic of the previous method will also hold in this case.

Pressure through flow

In the approximation, we can assume that knowing the flow of liquid flowing out of the open tap, you can determine what the water pressure in the system is. But for this it is necessary to produce quite complex and lengthy calculations, which must take into account:

  • material and configuration of the pipeline;
  • diameter of the pipe;
  • the nature of the fluid flow;
  • degree of opening of the crane.

To determine the pressure, you will need a calibrated calibrated container (in the simplest case, a 3-liter can) and a stopwatch. When the water pressure is switched on, the filling time of the container is detected.

On the basis of the obtained data, a theoretical calculation of the pressure in the network can be made. However, as already noted, due to sufficient complexity, the result will be very inaccurate. It is much easier to interpret the experimental data in qualitative terms. So, if the dimensional 3-liter capacity is filled in more than 10 seconds, then the pressure in the system is clearly less than the regulated value. Approximately enough pressure for normal functioning of household water-consuming devices can be considered pressure, which provides filling of a capacity of 3 liters in 7 or less seconds.

From the description of the most common methods for measuring pressure, it can be concluded that the most accurate and simple for practical implementation is the method using a standard purchased manometer.

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