Re: I need some help

[jlandry@domain.elided (John A. Landry)]

The black helicopters hovering over the house recorded <hofs@domain.elided>
whispering:

>I can't find a normally closed solenoid. Help!

John,

What you want is a Square-D Pumptrol(R) Pressure Switch.  They make an
inexpensive commercial pressure switch that should be exactly what you
need.  It would REPLACE the existing pressure switch on the compressor and
is a known as a REVERSE Action Switch.  That is, the contacts OPEN on
falling pressure verses closing on falling pressure.  In this way you would
not need to add another solenoid (relay) in between the throttle solenoid
and the compressor outlet.

The switches I listed below are fully adjustable and they "cut in" (close)
in the range of 65 to 150 psi.  They "cut-out" (open) in the range of 35 to
120 psi.  The differential pressure between the cut-in and cut-out points
is adjustable between 30 to 45 psi.  For example, this means you could set
the switch to close the contacts at say 150 psi and open at approximately
120 psi.  These ranges should work nicely for an air compressor.  I have a
version of this same type switch on my truck air compressor conversion.


Square-D Part Numbers


Single Pole                           Two Pole

Class 9013, Type FRG-92              Class 9013, Type FRG-82

The above features 1/4" NPSF Internal (Female) threads


Class 9013, Type FRG-93              Class 9013, Type FRG-83

The above features 3/8" NPSF Internal (Female) threads


Class 9013, Type FRG-98              Class 9013, Type FRG-88

The above features 1/4" Flare fitting


Class 9013, Type FRG-99              Class 9013, Type FRG-89

The above features 1/4" NPT External (Male) threads


To the above part numbers, you MUST add a code to the end of the number
which specifies the factory pressure setting.  The closest one available
(stock) is J25, which means 60 psi open and 80 psi closed.  Remember that
you can change this once the switch is put into service.  Code J99 is for a
custom pressure setting that you can specify (within the ranges I explained
above).  A custom pressure setting might make the lead time a bit longer
from the factory.  So a complete part number would be Class 9013, Type
FRG-82J25.

If for some reason you need to retain the "normal" action of the pressure
switch (like the one you have now) IN ADDITION to the "reverse" action, you
can have that too in the same switch!  Just order a two pole switch from
the list above and add an "H" to the end of the entire part number.  For
example, Class 9013, Type FRG-82J25H.  Then one pole will be normally open
and one will be normally closed.

Any Square-D distributor should be able to easily order this switch for you
from factory stock.  Look in the Yellow Pages under "Electrical Supplies."
You can also have W.W. Grainger (www.grainger.com) order special Square-D
switches for you (they don't stock these).  The typical price will be about
$30.00.  If you want the "H" suffix, you can expect to pay a couple of
dollars more.

>There may also be some other answer that neither he nor I have thought 
>of. 

I can't imagine that ever happening!

Good luck,

John
------------------------------------------------------------------------
jlandry@domain.elided             |
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