The followings are the performance indexes of valves should be noticed in usage.

Sealing performance of valves 

Sealing performance of valves refers to the capacity of every sealing part in valves to prevent media from leaking. It is the most important performance index for valves. Valves have three sealing parts: connection between disc and sealing face of seat, connection between packing, stem and stuffing box, connection between body and bonnet. Leakage happening on connection between disc and sealing face of seat can be considered inner leakage, which has great impact on the capacity of valves to stop media. In terms of block valves, inner leakage is not allowed. Leakage occurring on other two connections is out leakage. Media leak from valve inside to valve outside. Out leakage causes media losses, environment pollution or even accidents. For media having combustion and explosion, toxicity and radioactivity, out leakage is also not allowed. For this, valves must have reliable sealing performance. 

 

Media 

Media passing through valves can produce pressure losses. Valves have resistance to flow of media. Media must lose part of energy to overcome the resistance of valves. Concerning for energy conservation, resistance of valves to flow should be reduced as far as possible when designing and manufacturing valves. 

 

Toque 

Torque refers to the torque for opening or closing valves. When closing valves, disc and two sealing faces of seat should form sealed pressure ratio and overcome the friction between stem and packing, stem and threads of nuts, support of stem top and other friction parts. So, closing force and closing torque are necessary. During operation, closing force and closing toque are varied. The maximum is the final moment of closing and initial moment of opening. Nevertheless, reducing closing force and torque also should be reduced possible when making and designing valves.     

 

Sensibility and reliability 

Sensibility means that valves react to coefficient of media. For throttle valves, reducing valves and control valves which are used to regulate media and safety valves, drain valves having specific functions, sensibility and reliability are very important. 

 

Service life

Service life represents durability of valves. It is also one of important performance indexes, having economic significance.