Some Basic Terminologies of Valve

The valve is some accessories used to open and close the pipeline, control the flow direction, adjust and control the parameters (temperature, pressure and flow) of the transmission medium.

Basic Terminology

1. Strength Performance

The strength performance of the valve refers to the ability of the valve to bear the medium pressure. The valve is a mechanical product bearing internal pressure, so it must have enough strength and rigidity to ensure long-term use without fracture or deformation.

2. Sealing Performance

The sealing performance of the valve refers to the ability of each sealing part of the valve to prevent medium leakage, which is the most important technical performance index of the valve.

There are three sealing parts of the valve, the contact between the two sealing surfaces of the opening and closing parts and the valve seat, the fitting between the packing and the valve stem and the packing box,

 and the connection between the valve body and the valve cover. The former leakage is called internal leakage. That is to say, the valve is not tightly closed, which will affect the ability of the valve to cut off the medium.

For block valves, internal leakage is not allowed. The last two leaks are called leakage. That is, the medium leaks from the inside to the outside of the valve. Leakage will lead to material loss, environmental pollution and even accidents.

For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance.

3. Flow Medium

When the medium flows through the valve, there will be pressure loss (that is, the pressure difference between the front and back of the valve). Namely the valve has a certain resistance to the flow of the medium, and the medium will consume a certain amount of energy to overcome the resistance of the valve. In terms of energy conservation, when designing and manufacturing the valve, the resistance of the valve to the flowing medium should be reduced as much as possible.

4. Opening and Closing Force and Moment

The opening and closing force and moment of force refer to the force or moment that must be applied when the valve is opened or closed.

When closing the valve, it is necessary to form a certain sealing pressure between the two sealing surfaces of the opening and closing parts and the engine seat. At the same time, it is necessary to overcome the friction between the valve stem and the packing, between the thread of the valve stem and the nut, between the end support of the valve stem and other friction parts, so a certain closing force and moment must be applied. During the opening and closing process of the valve, the required force and moment are changed. The maximum value is at the the final instant of closing or the initial instant of opening. The design and manufacture of the valve should strive to reduce its closing force and moment. 

5. Opening and Closing Speed

The opening and closing speed is indicated by the time required for the valve to complete one opening or closing action. Generally, there is no strict requirement for the opening and closing speed of the valve, but some working conditions have special requirements for the opening and closing speed, such as some requirements for quick opening or closing to prevent accidents, some requirements for slow closing to prevent water hammer, etc.. It should be considered when selecting the valve type.

6. Operation Sensitivity and Reliability

This refers to the corresponding sensitivity of the valve to the change of medium parameters. For the throttle valve, pressure reducing valve, regulating valve and other valves used to adjust the medium parameters, as well as the safety valve, drain valve and other valves with specific functions, the functional sensitivity and reliability are very important technical performance indicators.

7. Service life

It indicates the durability of the valve, which is an important performance index of the valve, and has great economic significance. It is usually expressed by the opening and closing times that can guarantee the sealing requirements, or by the operating time.