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A FORUM FOR FIRE PROTECTION QUESTIONS & PE EXAM PROBLEMS | SUBSCRIBE NOW

Best Way to Setup Multiple FP Air Compressors?

11/24/2020

8 Comments

 
I inherited 3 sites each with multiple sprinkler systems (2 or 3 depending) on "plant air". The problem is the compressors assigned to deliver said plant air are only robust enough to air up a single component system within 30 minutes.

During the fall, we experience drastic temperature drops at dusk that result in pressure drops across all systems simultaneously, that effectually over-task the lone compressor at each site. The compressors run until the overtemperature cut-off pops, and they've been leaking oil from the head gasket due to overheating.

I'm perfectly willing to buy a $5k compressor, but they're typically 3 phase. I'm also willing to buy 2 or 3 small compressors/riser and cap the plant air line, but in either case the greater expense is running AC power to the risers, or upgrading the current plant air circuit voltage.

A permutation of the above 2 options would be to run 2 -$700 compressors in parallel at the current plant air site to split the CFM output requirement. I would have to run a 2nd dedicated circuit to the existing compressor locations, but it's in relatively close proximity to the panel.

To do so I am assuming I would need to wire the on/off pressure switches to an air maintenance device. I need them to come on and cut off at the same time, or else one will run to failure, the pressure bleed down, then the redundant compressor will run to failure. I'm worried that modifying the new compressors will void their warranties (which I acknowledge I may have to live with).

Does anyone have a diagram and parts list for how to use 2 compressors in tandem? Any recommendations for most pragmatic fix?

​Thanks in advance.

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8 Comments
Dan Wilder
11/24/2020 10:21:40 am

First, if your systems are losing that much air, even with the temp difference, that should be your priority not the band-aid of trying to keep up with the leaks.

You don't want a single switch to run both compressors at the same time, they will either short cycle each other both run needlessly when one could handle things. I would approach this more as pumps in parallel and have the compressors start at different low point PSI settings. Maybe even check valve the compressor air from plant air so any plant draw doesn't kick on the fire sprinkler compressors.

Maybe buying a air reservoir/receiver instead (no wiring required) would be a better option to lessen the overall impact of low air issue (again, check valve this from the plant air to lessen additional volume draw. Have any old compressors around you can salvage tanks from?

Just spit balling ideas...

Reply
John Rasmussen
11/24/2020 10:37:36 am

Agree strongly with eliminating leaks and adding air receiver tank. Also, what pressure do you maintain in the fire sprinkler system? Typically dry valve systems only need 30 psi and plant air will be 100+ psi. If your sprinkler system air pressure is too high it will leak worse and load compressors more.

Reply
Pete D
11/24/2020 11:44:39 am

Reliable Model D w/ 105psi city water. I think the regulators are set a little high at 40psi, which is the next line of the table. System volumes are unknown (let's say big). All systems have B-1 accelerators, so we can safely assume >750 gallons, but I think they may be as big as 1500 gal.
I landed on a 5HP Speedaire that runs on 1 phase 240. I have to pull a new #8 circuit and install a 50A breaker. The compressor delivers 14cfm at 140 psi and has a 60 gal reserve tank. I got off cheap- [$1250 compressor + $500 electrical + $100 in external regulator and 3/4hoses] x 3 buildings. I miscommunicated the scenario in the original post. Multiple sprinkler systems are configured as though they are on plant air, but the air lines only serve the sprinkler systems. There is no peripheral task for the compressors. Thanks for the feedback

Mike F.
11/24/2020 10:38:45 am

Talk to the guys at General Air Products!

Reply
Kelsey
11/24/2020 10:48:04 am

I second this!

Reply
Ray F. link
11/29/2020 12:58:54 pm

Thanks for the call out. We are always happy to help with questions like this. Pete D. my email is rmfjr@generalairproducts.com, while I understand you are using a Speedair compressor, I can still offer assistance on the set up if you like. Reach out and we can discuss.

Reply
Mark Harris
11/24/2020 08:07:20 pm

Agree with everything said above but if you really want two compressors I would use tank compressors and put check valves on discharge piping of each compressor and then a listed air maintenance device on each system. The check valves should keep the start stop on the two compressors from fighting each other. But just the extra tank suggested above could be more cost effective.

All the air supply in the world will not fix a leaky system. Not the time of year to do it if you are in cold weather location but quickest way to evaluate your piping issues if water damage could not be catastrophic (like a data center or attic system in a nursing home) would be to flood system with water. You may find multiple pinhole leaks. Sometimes issues are concentrated in main piping if thinwall pipe and branch lines are schedule 40 and drain well.

Once the system is tight may want to consider a nitrogen generator to slow future corrosion.

Reply
Pete D.
11/24/2020 08:18:24 pm

Thanks Mark. Not leaking anywhere to my knowledge.

Reply



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