size of valve opening

[f1fan]

Hi everybody
I am working on a system that has a line cross sectional area of 0.0491 in^2, a velocity of 18.50 in/s and a pressure of ~11 psi. I need to determine how large a valve opening should be made such that the pressure remains constant. Is this possible without knowing the pressure downstream of the valve? The cross sectional area remains the same before and after the valve.
Thanks for any help

 

[JStephen]

I'm not sure of your question, but I think you would have to have flow data from a specific valve; it would depend on the valve configuration, not just the opening area.

What is the fluid in question? And what pressure remains constant- upstream, downstream, or pressure drop across the valve?

 

[duika]

hi f1

i think that you must choose the valve with higher Cv of the market, because the fluid always is going to have head loss in the valve.

 

[schick]

f1-
Sounds like you're dealing with 2 unkowns, Cv and downstream pressure. You're going to need to pick one. If downstream pressure is not a factor, any valve will work. If you're concerned about agitation of the fluid you're valving, pressure drop may be a significant factor along with valve type selection.

Try picking a valve out of a catalog, use the given Cv and determine whether or not the pressure drop is acceptable.

Or, you could size you valve based upon the orifice size to maintain a minimum restriction of 1/8"

Hope this helps..

Schick

 

[sailoday28]

If the downstream pressure remains constant, any added valve will give a pressure drop. Therefore the upstream pressure will change
If the flow is choked (independent of back pressure), then the flow with the added valve is basically proportional to the upstream stagnation pressure (and inversely proportional to the upstream stagnation temperature)
Valve area will then impact upsteam stagnation pressre.
I don't see how you can keep upstream pressure constant, unless something like a pump with a variable H-Q curve.

 

[brainstorming]

I need to determine how large a valve opening should be made such that the pressure remains constant.
which pressure u need it to be constant?
There should be a pressure drop while you have a valve or a fitting in the line.

What is the fluid and the its temperature?
By isentropic, there will be conditions change across the valve.

Regards

 

[rcooper]

Would a pressure sustaining valve work in this application?

 

[duika]

a sustaining valve only remains constant the pressure upstream but not equal the pressure upstream and downstream.