This paper introduces the testing methods of the sealing performance of the control valve and the leakage amount of the mechanical seal of the alkali pump, and probes into the solving methods of the leakage of the control valve.

How to operate the sealing test of the control valve?

The tested regulating valve is installed in the experimental pipeline. One end is filled with pressurized water (or air), the other end is blocked by blind plate and O-ring. Pump water pressure, or air compressor, nitrogen tank supply gas pressure, pressure effect to the valve body. During the experimental balanced mechanical seal time, the number of valve stem actions is more than 3 times per minute. The valve body, upper valve cover and lower valve cover are quietly hit by the experimental hammer. Then, the leakage of packing box and sealing part is carefully checked. If air or nitrogen is used for mechanical seal test of water pump, soapy water can be applied to all inspection parts to observe whether there are bubbles. You can also immerse the control valve in water to see if there are bubbles overflowing. The use of air as the experimental medium is a little bit of the measurement error is small, no corrosion effect on equipment, cleaning the workplace. Regulating valve in the pipeline device, you can also choose a special hydraulic clamping equipment.

What should be paid attention to in the test of valve sealing? What are the rules of national standards for sealing?

The precautions for the experiment are as follows:

1. When the experimental pressure is input at the inlet side of the valve, the other end must be sealed, so as to keep the experimental pressure stable.

2. During the experiment, the number of valve stem actions is more than 3 times per minute.

3. During the experiment period, the relevant parts, especially the sealing parts, should be hit quietly with the experimental hammer.

4. Leakage beads should not be removed in water experiment and bubbles should not be bubbled in air experiment.

The packing box and other joints of the National Standard Regulation Valve shall ensure that there is no leakage at 1.1 times nominal pressure. The test pressure of the regulating valve should be 1.5 times the nominal pressure, and the compressive strength test should be carried out for more than 3 minutes. There should be no visible leakage during the experiment period.

What is the definition of the leakage of the control valve? In order to achieve low leakage, which methods have been selected for the control valve?

Leakage refers to the flow of fluid through the valve under regular experimental conditions and closed conditions.

The experimental conditions include that the actuator has sufficient thrust, that the seat and spool can be pressed, and that there is a definite pressure difference between the front and back of the valve, which is carried out at room temperature.

There are many factors affecting the leakage of the control valve, such as the size of the pressure, the information of the sealing surface, the wear condition of the sealing surface, the stress and deformation of the valve internals, etc.

When using the control valve, some occasions expect that when the valve is closed, the smaller the leakage of the sealing surface between the spool and the seat, the better. Some technical conditions even require that the control valve should not leak. Therefore, in order to achieve the intention of low leakage, there are many kinds of construction and application data, such as soft sealing, i.e. using rubber or PTFE as the sealing surface.

What should be paid attention to in the leakage measurement test of control valve?

When testing, we should adhere to the certain fluid pressure in front of the valve, measure the leakage behind the valve, and pay attention to the following points.

1. Use the pressurized fluid input to the front of the valve to wash away stolen goods, dust and oil on the sealing surface of the valve seat.

2. The actuator or valve positioner makes the valve move several times and closes the valve after passing through the experimental air pressure.

3. The leakage can be measured only after the experimental pressure in front of the valve reaches a stable level.