I want to sense pressure in a line that feeds part clamps and turn on a
green light and/or have a red light go out so the operator will try to
remember to clamp the parts. (don't laugh) I could use a compressor switch
for about $30 and a search finds sensors for about $80. Can I use an
automotive oil pressure idiot light switch or something like those? They
are only $5-$10. Any other ideas?
Idiot light OPS are good to 100psi or so; usually NC, trigger at 3psi.
VW ones also can be NO to 1.8 bar.
JR
Dweller in the cellar
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What pressure. There are A/C system switches as well as oil pressure
switches and even brake light switches that operate using brake
pressure. The OP idiot light switches usually turn OFF (NC contacts) at
about 5-8 PSI. The A/C switches depend on which end of the system they
are on. The high pressure switches usually turn on about 120-140 PSI
(and there are adjustable ones)
The brake pressure light switches turn on around 100-150 PSI. (Ford,
Chrysler)
I'll bet that would work fine. It might eventually fail after 5 years
or so with the pressure going on/off/on all the time. Buy two.
There likely is a less expensive strain gauge type sensor available that
would last forever since there is no bellows constantly stretching.
Jon
Umm, these are good to thousands of PSI, my guess is the trip pressure
may be anywhere from 50 - 250 PSI on each unit. They may not work in a
system with just 100 PSI line pressure.
Jon
The part is spec'ed at "100 PSI", (+- something).
It looks to be a piston - activated device. What might cause the switch to
work properly yet activate at a pressure significantly different than 100 PSI?
The piston / cylinder could change diameter by more than a few percent.
(Unlikely.)
The return spring behind the piston could change pressure.
(Possible with temperature change though we can be pretty sure Tom's shop stays
cooler than the temperature commonly found in the area of a car firewall).
Piston stiction caused by 1000's of wear cycles could cause it to activate at
different pressures from cycle to cycle.
(Possible. The replacement part is not expensive.)
At three bucks one could afford to buy 20 and cherry pick for actuation
pressure.
Tom, you can also try the 'low pressure' version. It's not cheap, though.
I'll get a bunch of the $3 guys and test them. Shop air rarely falls below
110, but even at $18 they won't hurt my budget. (which is about $5k over
already)
I'm fond of Nason pressure switches. I needed a SPDT oil pressure
switch for my car that operated at 15psi but didn't want to pay an arm
and a leg for one. A standard oil pressure switch operates at 3-5
psi, which for me is way too late. The 15 psi gave me the warning I
needed, and on the engines I've used them on, the light would barely
flicker when the engine was really hot. Got it from my local Carquest
that ordered it for me. I think I paid in the $25 range, retail. The
thing is solid as a rock and very well built. I was never worried
about the stem breaking off from the vibration.
Anyway, the price was really good as well. A buddy of mine repeated
what I did, and they sampled him the one he wanted. Link is
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You pick out the
pressure range, connection type, etc, rather than figuring out how to
make what's on the market wire up to your existing system. They also
have adjustable ones, too.
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