Subject: Way too much cycling of compressor motor

From: [email-masked]
Date: 9 Dec 1996 15:53:01 GMT

Here goes my story. I saw a very nice 80 gallon 2-stage industrial
compressor. Motor, plumbing, etc was missing. Price was $35. I had a 5HP
motor. I went to Home Depot and bought a lot of pipe, even made a
radiator. The only thing lest was the pressure switch, which I got from a
surplus electronics store. It is labled as a "adjustable pressure switch
25-250 PSI". So I wire everything and when the pressure is reached, the
motor starts turning on and off in 1 second intervals. I blew a 100A fuse!
What have I done wrong? Thank you for your help.

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From: [email-masked]
Date: 9 Dec 1996 18:37:42 GMT

Dear Fellow Metalworker :

Your problem is, that the span on your pressure switch is set too low,
should be at least 30 psi. in an installation of your kind.

Alberto:

Keep up the good work.

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From: [email-masked]
Date: Tue, 10 Dec 1996 18:11:09 -0600

>I So I wire everything and when the pressure is reached, the

Does the switch have an unloader valve?  If the pressure sensing port were on the 
pump side of the check valve, then the switch would start the motor as soon as 
the unloader had dropped pressure to the cut-in point.

It is also possible that you installed the switch between the pump and the tank.  
If so, then there might be enough of a pressure surge (due to slight restriction)
to stop the pump too soon.

-KF-

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From: [email-masked]
Date: 9 Dec 1996 22:17:47 GMT

In article <[email-masked]>,
[email-masked] writes:

> So I wire everything and when the pressure is reached, the

Sounds like the pressure switch is connected between the tank check valve
and your compressor instead of on a separate line into the tank.  Did that
just this weekend when building a small one.

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From: [email-masked] (Chuck Sherwood)
Date: 9 Dec 1996 18:21:37 GMT

In article <[email-masked]>,
Ed Clarke <[email-masked]> wrote:
j
>>motor starts turning on and off in 1 second intervals. I blew a 100A fuse!

Where are you connecting the pressure switch? Is it connected to the tank,
or is it connected to the pipe between the pump and the tank? If its the
latter, it will see BIG pressure pulses from the pump.

-- 
--
Chuck Sherwood
[email-masked]

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From: [email-masked]
Date: 13 Dec 1996 17:26:46 GMT

In article <[email-masked]>, Elliott <[email-masked]>
writes:

>my vote is you need a pressure switch with a differential or hysterisis
> as one fellow wrote.
>  check ww grainger for one by furnas its about 35.00 and has adjustable
>differential set points.
> 

Hey Vantanova, what was the outcome of this? I for one would be interested
to know, providing you are still alive and not electocuted as a result.
Probably still like to know then.

Peter

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From: Elliott <[email-masked]>
Date: 13 Dec 1996 03:09:25 GMT

elliott

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From: [email-masked] (VAntonova)
Date: 13 Dec 1996 19:25:26 GMT

>Probably still like to know then.
I had four problems: the motor was too weak, no cooling for the
compressor, the pressure switch was between the compressor and the
receiver, before the check valve, and it was the wrong kind of pressure
switch. After fixing all of this, I ended up paying a total of $120, and
had a 10HP 80 gallon two stage compressor delivering about 15-20CFM at
150PSI. When I opened the compressor it was in great condition! Either it
was new or newly honed and rebuilt. I could see clear hone-marks on the
cylinder walls and the valves were brand new. The downside was that I
spent a total of at least 40 hours, mostly between 10PM to 5AM, set a pile
of greasy newspaper on fire, reseived a nasty electrical burn, and the
flywheel almost flew out!!! By the way, the place I bought this is the
gratest store imaginable (it's not really a store, it's a big repair
shop)! Here are some of the best deals:
20HP 3 phase motor $25
10HP 1 phase motor $35 (true 10HP)
200A mig welder, slightly rusty, free shpping $45
Superior Electric NC controller with 3 servos FREE
5'x25' (that's FEET) lathe $500 (Not even rusty; too big for my garage :-(
the compressor, 4 regulators, 100' hose, 80 gallon tank $40
8" divining head, great condition $50
Unfortunately, a new owner took over and the prices went up. :-(
Man, do I wish there were more places like this!!

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From: James Askew <[email-masked]>
Date: Fri, 13 Dec 1996 20:29:33 -0800

> Man, do I wish there were more places like this!!

Oh man I would like to have that "divining head" ....  I have
never seen one but maybe with it I could find that drive pin I lost
in the shop somewhere.

Jim

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From: [email-masked] (Ed Clarke)
Date: 9 Dec 1996 16:21:05 GMT

>What have I done wrong? Thank you for your help.

No hysteresis.  You want it to start at 90 psi or less and cut off at 120
(for example).  If this isn't adjustable on your switch, go buy another 
one of a different sort.