Pressure drop across a valve with air going thru ! Help ME!!
Pressure drop across a valve with air going thru ! Help ME!!
(OP)
Ok I am really stuck here and I need your help!
here is the information I have so far :
I am pulling facuum on a vessle using a jet, and I know the pressure at the jet and the pressure at the vessle. I have a valve mid-way and I need to know the pressure going into this valve and the pressure leaving the valve. I have measured and accounted for fittings from the vessel to the valve and after the valve up to the jet. I have calculated the pressure drops associated with the piping and fittings but I still do not know how to find the pressure drop across this valve.
inlet pressure : 49687 Pa
Size : 2 inch
Type : Ball Valve
Cv : 104
Type of FLow : Air ( this is a gas not water)
What is the correct formula to find the outlet pressure, this formula must take into account the Cv.
Also, what I want to do is see if this pressure drop will be different if I replace the valve with a 2 inch GLOBE valve with a Cv or about 50.
Please help me out on this one guyz...I would really appreciate it.
shup
here is the information I have so far :
I am pulling facuum on a vessle using a jet, and I know the pressure at the jet and the pressure at the vessle. I have a valve mid-way and I need to know the pressure going into this valve and the pressure leaving the valve. I have measured and accounted for fittings from the vessel to the valve and after the valve up to the jet. I have calculated the pressure drops associated with the piping and fittings but I still do not know how to find the pressure drop across this valve.
inlet pressure : 49687 Pa
Size : 2 inch
Type : Ball Valve
Cv : 104
Type of FLow : Air ( this is a gas not water)
What is the correct formula to find the outlet pressure, this formula must take into account the Cv.
Also, what I want to do is see if this pressure drop will be different if I replace the valve with a 2 inch GLOBE valve with a Cv or about 50.
Please help me out on this one guyz...I would really appreciate it.
shup





RE: Pressure drop across a valve with air going thru ! Help ME!!
You're not pulling much of what I call a vacuum with the vessel being at 0.5 atm.
Go to Crane's Tech Paper 410, page 3-4.
Pressure Drop = (3.62)(K * D *q^2)/d^4
where,
Pressure Drop = psi
K = for a 2" ball valve
D = gas density, lb/ft3
q = actual ft3/sec
d = internal diameter, inches
From my compiled database for valves:
a 2" Velan ball valve (split body) has a Cv of 130 for a reduced port and 430 for full port.
Cv = 29.9 * d^2/(K)^0.5
The above will give you the answer. You should be able to handle the math.
Art Montemayor
Spring, TX
RE: Pressure drop across a valve with air going thru ! Help ME!!
However, when you find the flow coefficent, Cv the formula asks for the d (diameter in inches) I was just wondering if the number value before the formula was put there to balance the units or not?
but thank you I think your reply helped a lot.
shup