Check Valves: Questions Answered

[RKD89]

http://en.wikipedia.org/wiki/Check_valve
from the above wiki link I have understood basic concepts on Check Valves


Suppose I Heat a gas ( air ) in a closed vessel.
It's temp and pressure increase. As soon as the pressure reaches ( or exceeds??) the cracking pressure , the valve opens and I transfer the heated gas to another vessel ( at a lower pressure and temp)
For How long will the Valve remain open
1: Till the pressure in the heated vessel drops below the Cracking pressure
or
2:Till the pressure in both the vessels is evened out ( ie the valve closes to prevent back flow)

Also are valves available that can be adjusted to work on different ( a small range of say 30-35 psi) pressures

 

[Q_Goest]

A check valve will close when the forces acting on the poppet or closing device (swing checks) equilabrate. Forces on the poppet forcing it open include the pressure times a differential area and possibly gravity. Forces closing include the spring load and possibly gravity. You can do a free body diagram on the valving element to determine what pressure it opens or closes at. Generally, the opening and closing value is the same.

Check valves don't always seal up well on closing though. Like any valve, as the contact stress on the seat drops off, leakage occurs. The sealing surfaces might be in contact over most of the area, but leakage through the seat will occur if there's insufficient contact.

There are valves that can be adjusted over the range you need. Swagelok for example has http://www.swagelok.com/search/find...-1&item=c80b8fbe-343c-49a5-8ef1-2a086c6523b7", but I'm sure there are many others. Might want to do a search on adjustable checks.

 

[RKD89]

thnx...