Excessive Pressure Drop in Pressure Reducing Valve

[MAPower]

I have a Fisher 627WH pressure regulator, used in anhydrous ammonia service. This valve was originally going to see up to ~750 psig and drop it down to 300 psig, but now is only seeing about 150 psig. I am seeing excessive pressure drop across it, ~100 psig! It doesn't make any sense, the valve should be wide open and only see minimal pressure drop (<5 psig). We took it out and inspected the internals and found no trash or debris in it. Any clue what could be causing the pressure drop?

 

[rzrbk]

The valve will allow much less flow with the current 100psi drop as it would with the original 450psi drop.

To answer your question a full set of conditions (original and current) is required.

 

[israelkk]

I am not familiar with Fisher 627WH pressure regulator. But regulator is not a valve. A pressure regulator usually has a loaded spring to determine the rated regulated pressure. If a valve was designed to give 300 psig when the inlet is 750 psig it will the regulated pressure as long as the flow rate will be under some flow rate value if larger flow rate is needed the inlet pressure should be increased to keep the 300 psig regulated pressure. you can not just change the inlet pressure to 150 without readjusting the spring to a new desired load. Even if the spring allows regulating to 145 psig you will not receive much flow when the inlet pressure is 150 psig. The inlet/regulated pressures are function of the flow too.

 

[MAPower]

Here are the conditions,

Original conditions:

Max inlet pressure - 730 psig
Outlet pressure - 600 psig
Temperature - 93 F
Max Flow - 16.2 gpm

Current conditions:

Inlet pressure - 170 psig
Outlet pressure - 30 psig
Temperature - 50 F
Flow - 625 lb/hr ~ 2 gpm

This valve (regulator) has a 1/4" orfice in it with a 1" body, could the diameter of the orifice be restricting flow? Is this a possibility? Or the liquid ammonia could be flashing as it goes through the valve, but this is a low flow rate, so I'd be surprised if cavitation is the problem.

 

[BigInch]

maybe this helps,

http://www.fisherregulators.com/technical/selectsize/

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

Also, You have flashing of the Ammonia, approximately 7% so the maximum throughput will be less than if there was 100% liquid.

 

[MAPower]

Wow! How are you able to tell we have flashing? I am no expert in chemistry, but would greatly appreciate if you could explain. That will definately explain some of the drop.

 

[pipehead]

get out your ammonia PH diagram and trace the the inlet and out let coditions, hint Delta H = 0.0.

Or run my $2000 process simulator.

 

[dcasto]

The flashing isn't the largest contibutor to your problem. israelkk is probabily on track.

The regulator has spring to keep the valve closed with 730 psig and 600 psig outlet. At the lower outlet pressure a spring with a lower spring coefficient is needed. The fisher book says you need a 627W with a low pressure spring. You should be able to get the parts to modify and not replace the whole valve.