Thursday, May 22, 2008
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Kunal, a student from India has asked a rather simple question.
What is the function of VALVE ?
This question has triggered me to take a little effort to tabulate :
Valve has been commonly used for system isolation and positive protection i.e. shutdown valve. Valve used for isolation purposes generally are ball, gate and butterfly.
ii) Throttling & control
Varying opening of flowing path area in valve would be able to limit quantity of fluid passing the valve and serve the throttling and control purposes. Valve used for throttling and control purposes generally are globe, needle, special designed control valve, etc.
iii) Overpressure & Vacuum protection
Valve also use for system overpressure & vacuum protection. For overpressure protection, fluid is contained in system during normal operation. Whenever the system pressure increase, the valve will open to relief fluid to ensure system pressure below maximum allowable working pressure of the system. Valve use for his purpose is generally spring loaded pressure relief valve and pilot-operated pressure relief valve. Similar principle apply to vacuum protection but the difference is only allowing fluid enter into system to avoid vacuum.
iv) Avoid back flow
Valve with piston, flapper, etc would allow fluid flowing forward. Whenever fluid flow backward, the piston & flapper will close the flow path and restrict fluid back flow. Valve is normally called check valve or non-return valve.
v) Pump minimum flow protection
Valve like ARC valve is a self-contained valve which contain the check valve feature while allowing flow diversion during low flow. This is a good combination in pumping system where it demand back flow protection to avoid impeller damage and minimum flow protection during low flow.