how to determine valve cracking pressure area?
how to determine valve cracking pressure area?
(OP)
Hello,
Fluid flow pressure from the right side. The cylindrical valve attached to spring is supposed to open at a given pressure.
In the picture attached what diameter to select to calculate the area to determine valve cracking pressure? 16mm or 19.8mm diameter? Theoretical there are 2 cracking pressure? Sorry if the answer is obvious :)
I ask because test results shows something strange.
Fluid flow pressure from the right side. The cylindrical valve attached to spring is supposed to open at a given pressure.
In the picture attached what diameter to select to calculate the area to determine valve cracking pressure? 16mm or 19.8mm diameter? Theoretical there are 2 cracking pressure? Sorry if the answer is obvious :)
I ask because test results shows something strange.





RE: how to determine valve cracking pressure area?
RE: how to determine valve cracking pressure area?
I uploaded new picture with gasket location to prevent leakage. In the test I recorded pipe wall tapping pressure gauge reading and hence static pressure. But do you think if the valve just cracks the velocity component of flow would have significant effect to consider total pressure?
You mean to say diameter 19.8mm will determine the cracking pressure?
Strange result from the test is that cracking pressure area is neither from 19.8mm nor from 16mm but from the average of above diameters. 19.8+16.0/2 = 17.9mm dia. Area equivalent to 17.9mm dia determines the cracking pressure. Am I missing something in physics? Is it obvious?
RE: how to determine valve cracking pressure area?
RE: how to determine valve cracking pressure area?
If so then the moment the plug starts to move, the effective area will increase from 16mm as the thin film of liquid between the gasket and the seat will still have some pressure until it decays in the U shaped area. Hence an effective area of over 17mm seems quite reasonable to me. You can't go from cracking pressure to atmospheric in 0.1mm.
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RE: how to determine valve cracking pressure area?
RE: how to determine valve cracking pressure area?
@LittleInch the flow goes to sump (or its open to atmosphere). I think calculation of cracking pressure shouldn't be so complicated. Valve supposed to open at 3.5 bar and hence spring force calibrated accordingly.
RE: how to determine valve cracking pressure area?
You're not far away with average diameter to size the spring then just adjust to get the right pressure.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: how to determine valve cracking pressure area?
RE: how to determine valve cracking pressure area?
RE: how to determine valve cracking pressure area?
HarshParek: Let me just add the comment that in 'real use' you will of course have a dynamic and different situation varying with state of the valve, maintenance, wear, dirt, sealing condition, spring condition etc. etc.
The measurement of (theoretical) cracking pressure and accuracy will in lesser degree vary with theese factors and for one off brand new prototype, but will also be depending on the measurement devices accuracy, placement and the dynamic situation at the cracking moment and the instruments ability to record/react at the exact cracking moment without delay or measurement peaks.
An 'exact' area calculation might thus be colored by one or several of the points above.