Hi Flow Pressure Regulator for Air

[tomsaxon]

Hi-

I have a couple of basic questions for a control system under design...this is a PLC driven on-off pnuematic start system for aircraft using plant air, dried and delivered at approximately 120 psi, reduced to approximately 60 psi connected directly to jet turbines. As part of the control system design we were asked to size a 3" regulator capable of 3000cfm. The flow will go from zero to full rate in approximately 2 seconds (valve opening time programmed) so the regulator will have a fairly slow cycle but will have a very high flow rate intially until service pressure is established in a 20' line.

I have been told a couple of things by vendors that seem funky to an electrical engineer like myself--I'm looking for some good opinions from folks smarter than me!

1. Pressure ratings...an ANSI 125 is OK in this app due to the low temp. True of false.

2. Flow for gas is not directly rated with regulator size hence I can downsize to 2.5 inches and achieve a Cv that will allow 3000 cfm. Opinions....does size really matter?

3. Carbon steel regulator bodies offer no advantage over cast for a low temp, low pressure, non-corrosive environment. Boy can I save some money here!

Thanks in advance...I'd also like a basic level reference on regulator sizing for my own self study if you have a good author!

 

[dcasto]

ANSI 125 is good for 200 psig. Class 125 is almost always a cast iron body on valves. The flanges are flat faced. Temperatures under 150 F have little effect on pressure rating, so the low temperature you were refered to is under 150 F is correct.

Flow through a valve is based on the trim size that achies the desired Cv at the percent open you would like to operate. The Cv versus percent open can be adjusted by the geometry of the valve trim. Typically they a called , Quick open, Linear or equal percentage, or slow opening. Because we understand and can do 3 dimensional metal work, equal percentage valxes are most commly specified.

There are some valves that may achieve your desired Cv at 2".

Google fisher valves or regulators, they are the best source.

 

[Ashereng]

Flow for gas is affected by many things:
- orifice size
- inlet pressure
- outlet pressure
- the gas itself (eg. composition)


Typcially, a pressure regulator regulates the pressure, and the orifice is selected for the desired flow rate. Most regulators have a sizing chart that gives the rated capacity of the regulator at the full pressure drop.

If you google "Fisher regulator" and "Bulletin 71.1:627", you will get the technical datasheet for the Fisher 627 regulator.


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