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Re: siamese compressors

To: Douglas Shook <>
Subject: Re: siamese compressors
From: Eric Murray <>
Date: Fri, 3 Sep 1999 09:45:12 -0700
On Fri, Sep 03, 1999 at 08:32:44AM -0700, Douglas Shook wrote:
> Eric Murray wrote:
> > 
> > On Thu, Sep 02, 1999 at 06:42:40PM -0400, Fred Zampa wrote:
> > >
> > > Hello all:
> > >          I have two large Gilbarco gas station compressors
> > > which I would like to run in tandem in the hope of getting enough air to
> > > sandblast without frustration.
> > >
> > > How do I go about hooking them up ?
> My neighbor did this with a pair of 5hp
> compressors, and it is not as easy as you might
> think.  If you just hook up the outlets, then only
> one compressor motor will run (the cut-in points
> will never match exactly), so as someone
> previously stated, the second one is little more
> than a second tank.

It's unlikely that both compressors will have the same cut-in/out points.
So, say that compressor A is set up for cut-in at 110 and out at 140, and
compressor B is set up for cut-in at 100 and out at 130.
Both compressors are piped into the air system without valves.

Start the thought experiment with the entire air system @ 141.
As you start using air, the pressure in the system drops.
-if the pressure doesn't drop below 110, nothing happens, stop using tool, end.
-if the pressure drops below 110, compressor A starts.
-if A can keep up with your air use, the pressure will stay
 the same or rise to the cut-out point stopping A, stop using tool, end.
-if your air use is greater than A's output volume, the pressure will
continue to drop, albeit more slowly.
-if the pressure in the system drops below 100, B will kick in, adding
it's volume to A's. 
-if you're still using more air than both A and B can provide, both
compressors will run until you're done with the tool, at which point
they will refill the system and stop at their respective cutouts.
-if not, B will refill the system until it hits it's cutoff (130)
at which point it will stop, and the cycle repeats until you stop
using the tool.

So, if you use more air than the compressor with the higher cut-in
point can provide, in the system will cycle between the cut-in/out
points of the compressor with the lower cut-in point while the
higher compressor runs continually.


> I don't know which will work best for you, but it
> will be more involved that just connecting the
> outlets if you actually want to take advantage of
> the second motor and pump.

As I show above, you will take advantage of both compressors when the
added volume is required.

Eric Murray  ericm at the site  PGP keyid:E03F65E5

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