Valve Basic Technical Terms

1.Strength performance

The strength performance of a valve refers to its ability to withstand medium pressure. Valves are mechanical products that withstand internal pressure, therefore it must have sufficient strength and rigidity to ensure long-term use without rupture or deformation.

2.Sealing performance

It refers to the ability of each sealing part of the valve to prevent medium leakage, and it is the most important technical performance indicator of the valve.

There are three sealing parts: the area between seat and closure member; the area between stem and packing; the connection area between body and bonnet.

3.Medium

After the medium flows through the valve, there will be pressure loss (i.e. pressure difference between the inlet and outlet of the valve), which means that the valve has a certain resistance to the flow of the medium. To overcome the resistance of the valve, the medium needs to consume a certain amount of energy.

4.Open and close force and openand close torque

Open and close force and open and close torque refer to the force or torque that must be applied to open or close a valve.

When closing the valve, it is necessary to form a certain sealing pressure ratio between the sealing surface of the closure member and the seat. At the same time, it is necessary to overcome the friction between stem and packing, the thread of the nut and stem, the support at the end of the valve stem, and other friction parts. Therefore, a certain closing force and closing torque must be applied. During the opening and closing process of the valve, the required opening and closing force and torque vary, and their maximum value is at the final moment of closing or the initial moment of opening. When designing and manufacturing valves, efforts should be made to reduce their closing force and closing torque.

5.Opening and closing speed

The opening and closing speed is expressed in terms of the time required for a valve to complete an opening or closing action. There are generally no strict requirements for the speed, but some working conditions have special requirements for it. Some require quick opening or closing to prevent accidents, while others require slow closing to prevent water hammer. It should be considered when selecting valve types.

6.Service life

Service life represents the durability of valves and is an important performance indicator. Usually it is expressed in terms of the times of opening and closing that can ensure sealing requirements, or in terms of usage time.

7.Seal test

The test to inspect the performance of the closure member and valve body sealing pairs.

8.Back seat test

The test to inspect the sealing performance of stem and valve bonnet sealing pairs.

9.Seal test pressure

The specified pressure for valve seal test.

10.Flow area

The minimum cross-sectional area between the inlet end of the valve and the sealing surface of the valve seat. It is used to calculate the theoretical output volume without any resistance effect.

11.Flow diameter

The diameter corresponding to the flow area.