Low Pressure Air throttle valve 1

[mauner]

I am designing a low pressure air system to supply dry air to an electronic cabinet.

The supply pressure must be reduced from 2.5 psig to approximately 0.02 psig (0.55 inH20) to supply a flow of 6 SCFH.

What type of throttle device would provide the best control at such a low outlet pressure and flow?

A. pressure regulator
B. needle valve
C. orifice and valve

Any advice, suggestions or links would be greatly appreciated!!

 

[JimCasey]

It is hard to set a regulator to 0.02 psi because the force to move the valve's mechanism comes from the difference between the downstream pressure and atmosphere. Translation: You would need a valve with a HUGE diaphragm.

One possibility you did not list is a purgemeter. This is a small rotameter with a pilot valve (FLOW regulator) on it that senses the flowrate and maintains a constant flowrate regardless of changes in the downstream pressure. OR if your electronic cabinet is not sealed,The downstream pressure will always be atmospheric. Then just use the rotameter with a valve on it. There are also pilot valves to compensate for varyingupstream pressure, if your air system supply pressure swings much.

There are others, but I have had much experience with this:

http://www.emersonprocess.com/Brooks/sp210/pdfs/DS-1350E-03-05.pdf

 

[Ashereng]

I would try needle.

Here is another thought. Tube the air inlet into the cabinet through a "filter box". If too much pressure, add more filters or go to denser filters. If not enough, take out some filters or go to less dense filters.



"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[zekeman]

Keep it simple. A needle valve seems to be the simplest ; you don't need any fancy control systems for this one. It's a nobrainer. For your needs which are minimal and since you are holding the supply pressure at a fixed value, you do this by trial and error. This is not rocket science. The trouble with a lot of engineers is that they tend to use all the powerful tools now available for mundane problems.

 

[Compositepro]

There is a standard way for purging air through electrical cabinets. A needle valve controls the airflow into the cabinet (usually as part of a rotameter so you actually know what the flow rate is. The air exhausts to atmosphere though a ball- (or swing-) check valve so that a small back- pressure is maintained on the cabinet though a wide range of flow rates.