check valves
check valves
(OP)
what is the philosophy behind the use of two check valves of dissimilar types connected in series to each other?
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RE: check valves
RE: check valves
RE: check valves
RE: check valves
RE: check valves
RE: check valves
RE: check valves
Probability of failure of demand (PFD) is equivalent to the unavailability of a system at the time of a process demand.
Hazardous nature of the process determines the probability of failure tolerated in a safety application
If we use one return valve then the probability of failure to execute the required safety operation (i.e Prevent Back flow)is more. To reduce the PFD (i.e Increase safety)we use two check valves. Since the chance of both return valves failing at the same time is less the PFD is reduced.
I think that we can even reduce the PFD by selecting the return valve of dissimilar types.For example if there is a design problem in a return valve the chances of both failing at the same process condition is more.
In Safety systems like PLC its called as Safety Integrity level (SIL). You can learn more about in following links.
http://www.dyadem.com/services/rlm/sil.php
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