Steam Valve Sizing Effects
Steam Valve Sizing Effects
(OP)
I want to make a comparison calculation for the effects of increasing the voloume of steam into one of our machines. To save money we want to use the same steam valve and just increase the diameter of piping after the steam valve. The other option is to increase the size of the steam valve as well as the piping.
How can I calculate this to determine whether there is a difference?
How can I calculate this to determine whether there is a difference?





RE: Steam Valve Sizing Effects
RE: Steam Valve Sizing Effects
Let me try, though.
Q=((P1-P2)/L)^0.5 x D^1.5 / f x k
Q=flow rate
P1=pressure at start point of pipeline
P2=pressure at end point of pipeline
P1,P2 are regarded as unchanged
D=ID of pipe
L=equivalent length of pipe line based on D
f=friction factor
k=proportional constant
f decreases with increasing D, but not much. So let's say f is unchanged.
Then the equation becomes
Q=(1/L)^0.5 x D^1.5 x k1(k1 is new proportional constant)
L=L1+L2
where L1=eq. length of pipe,
L2=eq. length of valve
Then the equation becomes
Q=(1/(L1+L2))^0.5 x D^1.5 x k1
L1=length of straight pipe + sum of (K x D / f ) of all elbows
Usually K x D / f is significant compared to legth of straight pipe. Let's say f=0.02, K=0.6. Then KD/f for one elbows is 30D. Now you can figure out how long L1 is.
L2=(Kv*D/f)x(D/D2)^4
where D2=ID of valve inlet(ID of outlet should be same as inlet. D2 is not the diameter of inside of valve), Kv=10 for globe valve, 0.19 for gate valve.
Let's say f=0.02, D2=10", D=12".
Then L2=(10*12/0.02)x(12/10)^4 = 12432"(globe valve)
L2=(0.19*12/0.02)*(12/10)^4=236"(gate valve)
I don't know how long L1 is. Let's just say 6000".
Then Q=(1/(6000+12432))^0.5*12^1.5*k1(globe)
Q=(1/(6000+236))^0.5*12^1.5*k1(gate)
As you can see, globe valve affects very much while gate valve affects just a little bit. So if the valve is globe type, there is little possiblity you can avoid replacing it.
Hope this helps.
RE: Steam Valve Sizing Effects
Do some checking first. The biggest single problem I see with steam equipment, control valves, traps etc is gross oversizing. If you do increase sizes and/or supply pressure, be sure to check the capacity on any associated components like safety valves.
RE: Steam Valve Sizing Effects
You know the steam supply pressure and you know the pressure you want at the machine. At the new flow rate, will the control valve just open up more to pass the additional amount of steam and deliver that flow at the required pressure? If not, can you save enough pressure through bigger piping downstream of the control valve to offset the pressure drop resulting from the higher flow? Can you replace the trim in the valve (assuming it's a conventional control valve)?
Essentially, you need to look at the hydraulics through the entire sytem to made a conclusion. If the existing pressure drop through the downstream piping isn't that large, then replacing the piping isn't going to help you much but you need the specifics of the system to look at that in any detail.
RE: Steam Valve Sizing Effects
If you look at it as a simple pipe size increase without considering the load, orifice steam flow data shows that your Y (flow) varies with X (diameter) squared. System flow after increasing the pipe size from 12" to 16" (133%) will cause flow to go up 178%. This does not, however, take into consideration the actual system, friction losses due to pipe length, and the demanded load. Your answer might just be to install the new component without changing anything... I say put the new thing in a see what happens! If anyone asks, tell them some guy in a forum said it was okay.