Industrial valves are used to open and close the pipeline, control the flow direction, regulate and control the parameters of the conveying medium (temperature, pressure and flow) of the pipeline accessories.
1. Strength performance
The strength of the valve is the ability of the valve to withstand medium pressure. Valves are mechanical products under internal pressure and must have sufficient strength and stiffness to ensure long-term use without rupture or deformation.
2. Sealing performance
The sealing performance of valve refers to the ability of sealing parts of valve to prevent media leakage, which is the most important technical performance index of valve.
There are three sealing parts of the pipeline valve: the contact between the opening and closing parts and the sealing surface of the seat; Packing and stem and stuffing box matching; Body to bonnet joint. A leak at the front of the valve is called an internal leak and is often referred to as a loose closure, which affects the valve’s ability to block the medium.
For block valves, internal leakage is not allowed. The latter two leakage is called external leakage, that is, the medium leakage from the valve to the valve. Leakage will cause material loss, pollution of the environment, even serious accidents.
For flammable explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance.
3. Mobile media
After the media flow through the valve will produce pressure loss (both before and after the valve pressure difference), that is, the valve has a certain resistance to the flow of media, media to overcome the resistance of the valve will consume a certain amount of energy.From the consideration of energy saving, when designing and manufacturing valves, to reduce valve resistance to the flow of media as far as possible.
4. Opening and closing force and moment
Opening and closing forces and moments are the forces or moments that must be applied to open or close the valve.
Close the valve, the need to make the open-close part and send a form a seal between the two sealing surface pressure, but also overcome between stem and packing, the valve stem and between threads of the nut, valve rod end bearing friction and other parts of the friction force, and therefore must exert closing force and close moment, in the process of opening and closing, the valve is required for opening and closing force and the open-close torque changes, its maximum is in the closed end transient or open the initial transient. The valve should be designed and manufactured to reduce its closing force and closing moment.
5. Opening and closing speed
The 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 the valve, but some working conditions have special requirements on the opening and closing speed, such as some equirements for quick opening or closing, in case of accidents, some requirements for slow losing, in case of water hammer, etc., which should be considered when choosing the valve type.
6. Sensitivity and reliability
This is the sensitivity of the valve to changes in medium parameters and to respond accordingly. For throttle valve, pressure reducing valve, regulating valve and other valves used to regulate medium parameters and safety valve, trap valve and other valves with specific functions, its functional sensitivity and reliability is very important technical performance indicators.
7. Service life
It represents the durability of the valve, is an important performance index of the valve, and has great economic significance. Usually in order to ensure that the seal requirements to open and close the number of times, can also be used to express the time.
Classification of valves by purpose or main structural features
According to the valve type, transmission mode, connection form, structural characteristics, seat sealing material and nominal pressure of the valve number.
10. Connection dimensions
Dimensions for valve and pipe connections
11. General dimensions
Valve opening and closing height, hand wheel diameter and connection size.
12. Type of connection
Valves are connected to pipes or machinery in various ways (such as flange connections, threaded connections, welded connections, etc.).
13. Seal test
Test the performance of opening and closing parts and valve body sealing pairs.
14. Back seal test
Test stem and bonnet sealing accessory.
15. Seal test pressure
The pressure specified for the sealing test of the valve.
16. Suitable medium
Valve suitable medium.
17. Suitable temperature
Valve medium temperature range.
18. Sealing face
The opening and closing pieces fit tightly with the seat (body) to seal the two contact surfaces.
A general term for a part used to cut off or regulate the flow of a medium, such as a disc in a gate valve, a disc in a throttle valve, etc.
Fill the stuffing box (or stuffing box) to prevent media from leaking from the stem.
21. Packing seat
The part that holds the packing seal.
A part used to compress the packing to achieve a seal.
A part on the bonnet or valve body used to support stem nuts and transmission mechanisms.
24. Dimension of the connecting channel
Structural dimensions of connecting parts of opening and closing parts and valve stem assembly.
25. Flow area
Refers to the minimum cross-sectional area (but not the “curtain” area) between the valve inlet and seat sealing surface to calculate the theoretical displacement without any resistance effect.
26. Flow diameter
The diameter corresponding to the flow passage area.
27. Flow characteristics
Under the stable flow state, when the inlet pressure and other parameters are unchanged, the outlet pressure of the reducing valve is a function of the flow.
28. Flow characteristics derivation
Under the stable flow state, when the inlet pressure and other parameters are unchanged, the outlet pressure change value caused by the change of valve flow.
29. General valve
Valves commonly used in pipelines in various industrial enterprises.
30. Self-acting valve
A valve that operates by itself, depending on the capacity of the medium (liquid, air, steam, etc.).
31. Actuated valve
A valve operated by hand, electric, hydraulic, or pneumatic.
32. Hammer blow hand wheel
Hand wheel construction that USES impact forces to relieve valve operation.
33. Worm gear actuator
A device for opening and closing or adjusting a valve by means of worm gear.
34. Pneumatic actuator
A driving device for opening and closing or adjusting a valve by air pressure.
35. Hydraulic actuator
A driving device for opening and closing or adjusting a valve by hydraulic pressure.
36. Hot condensate capacity
The maximum amount of condensate that can be discharged in a trap at a given differential pressure and temperature
37. Steam loss
The amount of fresh steam escaping from the trap per unit time.