Jon Elson wrote:
Winston wrote:

Tom Gardner wrote:

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.

(...)

Three bucks for a 100 PSI brake light switch. Only 911 are left.
http://www.surpluscenter.com/item.as...-2400&catname=


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.
http://barrywhitesrrc.com/Merchant2/...gory_Code=PROD

Eighteen smackers, yikes!

--Winston