Compressed air receiver sizing

[rawelk]

I've become familiar with the rule-of-thumb for a minimum one gallon of receiver capacity per SCFM of compressed air generation from several online sources, but none I've read so far get into any details.

Three questions:

1). Does the 1 gallon/CFM rule of thumb apply only to installed air receiver volume, or does it also include system piping, local equipment surge tanks, coalescing filters, and the like?

2). Are there a dynamic measurement methods for determining optimum air receiver capacity?

I know this is a rather large question, because it depend on the type of compressor (in this case, all are rotary screw), where they are located ('wet' side, between compressor and dryer, or 'dry' side after the dryer), the nature of the specific demand load, and perhaps other factors.

3). I've bought, and started reading a 1980 copy of Ingersoll-Rand's "Compressed Air and Gas Data", but haven't seen this particular point addressed yet. Are their other recommended books that I should add to my library?

 

[hydtools]

You might try looking through the resources offered by the Compressed Air and Gas Institute, CAGI.

http://www.cagi.org/

Ted

 

[quark]

http://www.pyebarker.com/TechTips/techtip3.htm

1. No, it is the receiver volume

2. There is a method in the above link. Type of compressor and the receiver position with respect to dryer don't effect the receiver sizing.

3. Spirax Sarco has a collection of small and very informative booklets on compressed air. I don't know whether they still have it.

 

[rawelk]

Thanks to you both.

The Pye links are great, and along the way found another for air receiver sizing that was also helpful.

http://www.engineeringtoolbox.com/compressed-air-receivers-d_846.html

The CAGI reference was similarly helpful.

For the sake of completeness here is a highly schematic sketch of the compressed air system in question. Nameplate CFM (1485, 970, etc.) are shown at the top of the compressors.

http://files.engineering.com/getfil...d-3a12a6448139&file=compressed_air_layout.jpg

All of the fixed units run from a sequencer, and an IR Nirvana variable capacity unit (#7) runs stand-alone. It is rated for 990 CFM, and runs down to 31% capacity, or roughly 310 CFM minimum.

I must use a setpoint on the Nirvana of 10 PSI above the sequencer setpoint in order to have it (usually) control between 31% and 100% output, and figure this is to account for pressure drops between it and the sequencer pressure sensor.

Trended Nirvana % capacity (directly proportional to motor speed), and output pressure values via the Modbus data link.

I'm an electronics tech by training, and noted the resulting Nirvana % capacity trend looks remarkably similar to an oscilloscope trace of a loaded servo drive's DC bus link voltage when insufficient capacitance is across the bus.

That got me to wondering about the rough equivalent of electrical capacitance (air receiver volume) for a compressed air system, and it appears my suspicion of insufficient air receiver capacity is on the right track.

 

[quark]

I suspect the fluctuations to be more due to the layout of piping and header size. If you have more consumption in Dept.2 (comparitively), then you will have more fluctuations in that line. A ring header connecting the two compressor banks after coalescing filter and then taking branch off for usage will ensure less pressure fluctuations.

 

[foodprojengr]

I just purchased Compressed Air Operations Manual by Brian Elliott and it seems to be pretty thorough so far. I'm new to air compressors and it includes basic as well as detailed info.

Dave