Technical Terms of Valves

Valves are pipeline accessories used to open and close pipelines; control flow direction; adjust and control parameters (temperature, pressure and flow) of conveying medium. Valve terminology is important in daily operation. Let's have a look!
 
1. Strength performance
 
The strength performance of the valve refers to the ability of the valve to withstand medium pressure. The valve is a mechanical product that bears internal pressure, so it must have enough strength and rigidity to ensure long-term use without cracking or deformation.
 
2. Sealing performance
 
The sealing performance of the valve refers to the ability of all sealing parts 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 opening and closing parts and the two sealing surfaces of the valve seat; matching place of packing with the valve stem and stuffing box; connection with the valve body and the valve cover. The former leakage is called internal leakage, that is, it is usually said that the valve is not closed tightly, which will affect the ability of the valve to cut off the medium.
 
For block-type valves, internal leakage is not allowed. The latter two are called external leakage, that is, the medium leaks from inside the valve to outside the valve. Leakage will cause material loss; pollute the environment, and even cause accidents in severe cases.
 
For flammable, explosive, toxic or radioactive media, leakage is even more unacceptable, so the valve must have reliable sealing performance.
 
3. Flowing medium
 
After the medium flows through the valve, there will be pressure loss (that is, the pressure difference before and after the valve). 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.
 
Considering energy saving, when designing and manufacturing valves, the resistance of valves to flowing medium should be reduced as much as possible.
 
4. Opening and closing force and its torque
 
Opening and closing force and opening and closing torque refer to the force or torque that must be applied to open or close the valve.
 
When closing the valve, it is necessary to form a certain sealing pressure between the sealing surfaces of the opening and closing parts and the seat. At the same time, it is necessary to overcome the friction between the valve stem and the packing, between the valve stem and the screw thread of the nut, at the end support of the valve stem and other friction parts, so 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 opening torque vary, and the 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
 
Opening and closing speed is expressed by the time required for the valve to complete an opening or closing action. Generally, there is no strict requirement on the opening and closing speed of valves, but some working conditions have special requirements on the opening and closing speed, such as some requiring quick opening or closing to prevent accidents, and some requiring slow closing to prevent water hammer, etc., which should be considered when selecting valve types.
 
6. Action sensitivity and reliability
 
This refers to the sensitivity of the valve to the change of medium parameters. For throttle valves, pressure-reducing valves, regulating valves and other valves with specific functions, such as safety valves and steam traps, its functional sensitivity and reliability are very important technical performance indexes.
 
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 number of opening and closing times that can ensure the sealing requirements, or it can also be expressed by the service time.
 
8. Type
 
It is the classification of valves according to their use or main structural characteristics.
 
9. Model
 
Number valves according to their types, transmission modes, connection forms, structural characteristics, sealing surface material of the valve seat and nominal pressure, etc.
 
10. connection dimensions
 
The connection dimensions refer to the size of the connecting parts of valves and pipes.
 
11. General dimensions
 
General dimensions refer to the valve opening and closing height, handwheel diameter and connection size, etc.
 
12. Types of connection
 
Various ways of connecting valves with pipelines or machinery and equipment (such as flange connection, screw connection, welding connection, etc.).
 
13. Sealing test
 
It refers to the test of checking the performance of opening and closing parts and valve sealing pairs.
 
14. Back seal test
 
It refers to the test of checking the sealing performance of the valve stem and the bonnet sealing pairs.
 
15. Seal test pressure
 
It refers to the pressure specified during the sealing test of the valve.
 
16. Suitable medium
 
It refers to the medium applied to the valve.
 
17. Applicable temperature (suitable temperature)
 
It refers to the temperature range of the medium applied to the valve.
 
18. Sealing surface
 
The opening and closing parts are closely attached to the valve seat (valve body), and the two contact surfaces play a sealing role.
 
19. Opening and closing parts (disc)
 
It is a general term for a part used to cut off or regulate the medium circulation, such as the gate valve, the valve disc in the throttle valve, etc.
 
20. Packing
 
It refers to the packing in the stuffing box to prevent the medium from leaking from the valve stem.
 
21. Packing seat
 
It refers to parts that support packing and keep packing sealed.
 
22. Packing gland (gland)
 
It refers to parts for pressing packing to achieve sealing.
 
23. Supports (yoke)
 
It refers to the support on the valve cover or the valve body, the parts used to support the valve stem nut and the transmission mechanism.
 
24. Dimension of the connecting channel
 
It refers to structural dimensions of the assembly connection parts between the opening and closing parts and the valve stem.
 
25. Flow area
 
It refers to the minimum cross-sectional area between the inlet end of the valve and the sealing surface of the valve seat (but not the "curtain" area), which is used to calculate the theoretical displacement without any resistance.
 
26. Flow diameter
 
It refers to the diameter corresponding to the flow channel area.
 
27. Flow characteristics
 
In the steady-state, when the inlet pressure and other parameters are constant, flow characteristics refer to the functional relationship between the outlet pressure of the pressure-reducing valve and the flow rate.
 
28. Flow characteristics deviation
 
In the steady-state, when the inlet pressure and other parameters are constant, it refers to the outlet pressure change caused by the change of the pressure-reducing valve flow rate.
 
29. General valves
 
General valves are commonly used in pipelines in various industrial enterprises.
 
30. Self-acting valves
 
Self-acting valves are valves that operate by themselves depending on the capability of the medium (liquid, air, steam, etc.).
 
31. Actuated valves
 
Actuated valves are valves operated by hand, electricity, hydraulic pressure or air pressure.
 
32. Hammer blow handwheel
 
A Hammer blow handwheel is a structure using impact force to reduce valve operating force.
 
33. Wormgear actuator
 
The worm gear actuator is a device for opening and closing or adjusting valves with a worm gear mechanism.
 
34. Pneumatic actuator
 
The pneumatic actuator is a drive device for opening and closing or regulating valves by pneumatic pressure.
 
35. Hydraulic actuator
 
The hydraulic actuator is a drive device for opening and closing or adjusting the valve by hydraulic pressure.
 
36. Hot condensate capacity
 
At a given pressure difference and temperature, it refers to the maximum amount of condensed water that the trap can discharge within one hour.
 
37. Steam loss
 
It refers to the amount of fresh steam leaked from the steam trap per unit time.

Valve definition terminology

1. Valves
 
It refers to the totality of mechanical products with movable mechanisms used to control the flow of medium in pipelines.
 
2. Gate valve (slide valve)
 
It refers to the opening and closing part (gate) that is driven by the valve stem and moves up and down along the valve seat (sealing surface).
 
3. Globe valve (stop valve)
 
The valve whose opening and closing (disc) is driven by the valve stem and moves up and down along the axis of the valve seat (sealing surface).
 
4. Throttle valve
 
A valve that changes the cross-sectional area of the passage by opening and closing parts (discs) to adjust the flow and pressure.
 
5. Ball valve
 
It refers to an open-close (ball) valve rotating around a curve perpendicular to the passage.
 
6. Butterfly valve
 
It refers to an open-close (butterfly plate) valve rotating around a fixed axis.
 
7. Diaphragm valve
 
The opening and closing type (diaphragm) is a valve driven by the valve stem, which moves up and down along the axis of the valve stem and separates the actuating mechanism from the medium.
 
8. Plug valve (cock)
 
It refers to the valve that opens and closes (plug) rotating around its axis.
 
9. Check valve (non-return valve)
 
It refers to an open-close valve (disc) that automatically stops the countercurrent of the medium by the force of the medium.

10. Safety valve (relief valve)
 
The on-off disc automatically opens and discharges when the medium pressure in the pipeline or machinery and equipment exceeds the specified value. It refers to a valve that automatically closes when the value is lower than the specified value, which can protect the pipeline or the machine.
 
11. Pressure reducing valve
 
It refers to a valve that reduces the medium pressure by throttling the opening and closing parts (disc) and automatically keeps the pressure behind the valve within a certain range by the direct action of the pressure behind the valve.
 
12. Steam trap
 
A valve that automatically discharges condensed water and prevents steam leakage.
 
13. Draining Valve
 
It refers to a valve for the blowdown of boilers, pressure vessels and other equipment.
 
14. Low-pressure valve
 
It refers to a valve with nominal pressure PN≤1.6MPa.
 
15. Middle-pressure valve
 
All kinds of valves with nominal pressure PN ≥ 2.0 or PN < 10.0 MPa.
 
16. High-pressure valve
 
It refers to a valve with nominal pressure PN≥10.0MPa.
 
17. Ultrahigh pressure valve (super high-pressure valve)
 
It refers to a valve with nominal pressure PN≥100.0Mpa.
 
18. High-temperature valve
 
It refers to a valve with medium temperature > 450℃.
 
19. Low-temperature valve (sub-zero valve)
 
It refers to a valve with a medium temperature between -40℃ and -100℃.
 
20. Cryogenic valve
 
It refers to a valve with a medium temperature of less than -100℃.