Steam Flash Drum Level Control Valve

[Instr13]

Hi,
For controlling condensate level in a low pressure steam condensate flash drum we are using a globe valve 1-1/2" in a 4" pipe. Calculation shows that flashing occures inside the valve. Any suggestion for changing the existing trim and or changing the piping layout. Process conditions are P1=40.6 psig, P2=18.99 psig, Flow= 6500 kg/hr, Temp=141 deg C.
The valve is about 9 feet below drum outlet nozzel and the valve outlet pipe line runs UPWARD toward the condensate header.
Thanks.

 

[shobi]

By the sound of it, I think the problem is the dowstream piping has a long run and in upward direction. This will cause your valve to cavitate because of downstream pressure build up caused by high mixed phase velocity. Of course it does not help when the size of the valve is less than 1/2 of the size of the pipe. (1 1/2 valve in 4 inch pipe).
Followings are few guidelines:
1) Do not install a steam valve at the bottom of a down header.
2) Do not install a steam valve at the bottom of a down header without providing a steam trap near the inlet side of the valve.
3) Do not locate a condensate return valve more than 3 feet away from a flash tank or condenser.
4) Do not install a valve in a pipe more than twice the diameter of the valve.