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RE: Compressor-related motor question

To: <>
Subject: RE: Compressor-related motor question
From: "Randall" <>
Date: Thu, 15 Jul 2004 13:42:08 -0700
> As far as starting torque, before a decent-sized compressor is up
> to speed,
> you'd need a doggone large accumulator or else need to run unloaded a few
> revolutions (which is what lots of better compressors in this
> range in fact
> do - centrifugal unloader) to alleviate most of the starting load.  No
> realistic amount of longer pipe, etc. between the compressor and
> tank would
> do much there.

Not sure I understand your thinking here, Karl.  A quick check of HF's web
site turned up a compressor pump rated 5 hp, 145 psi, with a displacement of
20.5 cfm @ 1370 rpm or .015 cf/rev.  If we scale that back to a 1hp unit,
displacement would be .003 cf/rev or about 5 cubic inches.  3/4" copper
tubing has a cross sectional area of about 0.3sqin, so a 1.5 ft section
would provide about a displacement's worth of buffer.  So, at the end of one
revolution, the pressure would only be about 15 psi or about 10% of full
load.  Two revolutions gets us 20% and so on.

And if you double the length of pipe, still only 3' of 3/4" tubing, you
double the time to full load, etc.  Heck, if you wanted to, you could even
tee a smaller pressure vessel into the existing line ... something to do
with those propane tanks you've been saving <g>  Granted this would waste
some power at every startup, but so would an unloader.

Seems to me an unloader wouldn't be that hard to add either ... wire a
solenoid to the existing start switch inside the motor.  A suitable solenoid
should be only about $10 on eBay ... in fact there's a lot of two new ones
closing without a bid at $15 in about 15 minutes.


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