Hi all. I've got an air compressor that won't shut off when it reaches it's
maximum pressure. Am I correct that there is a pneumatic switch of some kind
to stop the motor? This is an old compressor, so is there an aftermarket
source and any help or comments are appreciated....thanks.

Michael wrote:
Hi all. I've got an air compressor that won't shut off when it reaches it's
maximum pressure. Am I correct that there is a pneumatic switch of some kind
to stop the motor? This is an old compressor, so is there an aftermarket
source and any help or comments are appreciated....thanks.

First.
Compressor tank explosions have killed quite a few people, and working
on a compressor which won't shut off without understanding it is a good
way to try for a darwin award.

The unloader is something different.
There is a one-way valve into the tank, from the compressor output.
Between the compressor output and the valve is a small controlled leak.
When the compressor stops, the valve shuts, and the leak drains the small
bit of pipe, so that the compressor can start easily, not have to start
against a load. (which it may not)

There will be a pressure switch, which should turn off the motor.
However, if you can't find this, you should really consider either having
it serviced, or buying one.

Alternatively, if you'd mentioned the make, people might be able to help
more, with hints on where you might get bits or manuals.

Michael wrote:
Hi all. I've got an air compressor that won't shut off when it reaches it's
maximum pressure. Am I correct that there is a pneumatic switch of some kind
to stop the motor? This is an old compressor, so is there an aftermarket
source and any help or comments are appreciated....thanks.



There are some compressors that unload the pump instead of shutting the
motor off. (I have one that was originally set up that
way, a Quincy.) It had a totally pneumatic unloader that held the
intake valves open when more air was not needed. If you have somthing
that looks like little pneumatic diaphragms on top of the compressor
head, with an air line connecting to it, that is an unloader. In this
case, you need a pneumatic control to switch the unloaders on and off.

If the power cord goes straight to the motor without going through
a little 3" cube box first, then there appears to be no electrical
pressure switch. Depending on the setup of the pump to tank connection,
an unloading-type pressure switch may or may not be needed to convert
it to an electrical pressure control.

But, most important of all, you want to make sure there is a pressure
relief valve, and that it works properly at safe pressure, generally
something like 10 PSI above your normal cutoff pressure. If in doubt,
get a new one from an air compressor dealer. That's what I did when I
refitted my Quincy.

Jon

But, most important of all, you want to make sure there is a pressure
relief valve, and that it works properly at safe pressure, generally
something like 10 PSI above your normal cutoff pressure. If in doubt,
get a new one from an air compressor dealer. That's what I did when I
refitted my Quincy.


Thanks, Jon. The relief valve works fine, as when it pops, I know to unplug
the unit. just kidding

I'll take it apart tomorrow and see what's inside the thing........Maybe I
can just add/replace the pressure switch ro something.....

Ian Stirling wrote in message
...
Alternatively, if you'd mentioned the make, people might be able to help
more, with hints on where you might get bits or manuals.

Thanks, Ian, but the unit is not handy right now. I'll go get it tomorrow
and list the specs.....

On Thu, 09 Dec 2004 00:03:32 -0600, Jon Elson
wrote:

There are some compressors that unload the pump instead of shutting the
motor off. (I have one that was originally set up that
way, a Quincy.) It had a totally pneumatic unloader that held the
intake valves open when more air was not needed. If you have somthing
that looks like little pneumatic diaphragms on top of the compressor
head, with an air line connecting to it, that is an unloader. In this
case, you need a pneumatic control to switch the unloaders on and off.

I service a bank of Huddlestons that do this.

Gunner



"If I'm going to reach out to the the Democrats then I need a third
hand.There's no way I'm letting go of my wallet or my gun while they're
around."

"Democrat. In the dictionary it's right after demobilize and right
before demode` (out of fashion).
-Buddy Jordan 2001

On Thu, 09 Dec 2004 00:03:32 -0600, Jon Elson
wrote:

Michael wrote:
Hi all. I've got an air compressor that won't shut off when it reaches it's
maximum pressure. Am I correct that there is a pneumatic switch of some kind
to stop the motor? This is an old compressor, so is there an aftermarket
source and any help or comments are appreciated....thanks.

There are some compressors that unload the pump instead of shutting the
motor off. (I have one that was originally set up that
way, a Quincy.) It had a totally pneumatic unloader that held the
intake valves open when more air was not needed. If you have somthing
that looks like little pneumatic diaphragms on top of the compressor
head, with an air line connecting to it, that is an unloader. In this
case, you need a pneumatic control to switch the unloaders on and off.

The idea behind this in an industrial setting is sound - if you use
a lot of air and have a VERY large compressor, you don't want to get
hit with the extra power charges for the motor starting surges several
times an hour. (Turn the motor off when everyone goes home.)

With a commercial "Demand Meter" panel, the utility not only
measures how much power you use, but how much you use at any one
moment. The higher the peak demand, the higher the power bill.

The head unloaders act like pushing in the clutch on your car. It's
cheaper to unload the compressor and let the motor and compressor spin
unloaded for a few minutes until there is another call for air. The
current draw of one compressor motor at idle is far less than
increasing the demand charges on the entire month's power bill for the
start surges bumping up your demand meter.
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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