FP System Air Compressor

[RossABQ]

I picked up a massive two cylinder Champion "Fire Protection System" air compressor. I am told it is typically used to pressurize a water tank at or near grade level, to give NFPA-required system pressures in multistory buildings without the use of a pump. In other words, rather than the head tank way up on the roof, like you used to see in the old days, you'd pressurize a large water tank that's down low, with air. Apparently the way these compressors were rated called for 40 psig discharge, and their capacity was measured in CFM of Free Air delivered in 30 minutes (duration of a fire?).

Does anyone have any history or experience on these types of compressors? I can't find anyone at the mfr. who can tell me if the compressor can be used for higher pressures. It certainly appears robust.

 

[stanlsimon]

Are you sure about the previous application for that air compressor? A more common present day method of delivering water to standpipes or sprinklers is to use a electric or diesel driven pump that pumps the water directly from water mains or atmospheric (unpressurized) tanks. It would be possible to construct a pressure vessel to hold 20 or 30 thousand gallons of water but probably not economical.

Air compressors are used in dry pipe sprinkler systems to fill the pipes with compressed air. These compressors have to be fairly large so that the pipes (sometimes 3"id x 100's of feet long)can be filled in a reasonable amount of time. These dry pipe systems are common in frozen food storage warehouses which can be very large and hence require big air compressors. When a head is set off, the air leaks out and the system is charged with water.

 

[RossABQ]

I agree, I am used to the dry pipe system applications, but when I called the Champion rep, that was the story they had. My compressor actually came from a dairy farm in California, used to feed a milking system.

 

[chief]

It is common on ships domestic potable water and fire sprinkler systems to use a Hydrophor tank ( pressurised tank)to give a storage battery effect. This eliminates the need for a constantly running pump. A high and low pressure switch , 'kicks' in and out the pump as required.
In the fire sprinkler case a smaller 'jockey pump' is used for top up and the larger pump will start in the case of fire demand.
The air compressor is used to top up the tank to the required pressure , usually in the 60 psi range. A 40 psi air compressor will give a head capability of just over 90 feet and may not be sufficient for a tall building.
In some case the tank has a rubber lung, and others the air is trapped above the water level.
The water level in the cylindrical tank is generally about 2/3rds, when fully charged with air.

Offshore Engineering&Design

 

[jimdfp]

The compressor you have would appear to be one for a dry pipe system.
Most dry pipe systems are regulated to about 40 p.s.i. The 30 minute cfm delivery time is the maximum time limit per NFPA 13 allowed for restoring air to the system after it has activated and then re-set.
Today's newest dry pipe valves are now requiring lower pressures, in the 18 to 20 p.s.i. range, which allows for quicker operation due to reduced exhaust time.
Your compressor is likely capable of much higher pressures, you just need the appropriate regulator.
Pressure tank sytems generally require a minimum of 75 p.s.i. and are pretty much obsolete. I've only seen one which was installed in the 1950's and taken out of service in the 1990's due to city water service becoming available.

 

[RossABQ]

Thanks for the responses! It's been an education!