Resetting the pressure switch

[Dale]

Our pressure switch is currently cutting off at 110lbs so we wanted to reset it to 120lbs. I thought we could just adjust the Allen screw on the side but it doesn't seem to have any effect. Is there something we're missing or are these permanently set at the factory and perhaps our gauge is at fault? Is there some pressuring sequence involved in setting them?

[Daniel_LaFleur]

Originally Posted by Dale

Our pressure switch is currently cutting off at 110lbs so we wanted to reset it to 120lbs. I thought we could just adjust the Allen screw on the side but it doesn't seem to have any effect. Is there something we're missing or are these permanently set at the factory and perhaps our gauge is at fault? Is there some pressuring sequence involved in setting them?

Pressure switches are typically set at the factory and cannot be set to a different value. Most of them are a diaphram, spring, and plunger setup.

Most likely you have loosened something on the switch and made it illegal for FIRST.

[Al Skierkiewicz]

Dale,
These devices are fairly imprecise so 110 psi is possible. There is no adjustment to my knowledge.

[Nate Laverdure]

According to the cutsheet for the Nason SM-2B-115R/443 pressure switch, the switch's setpoint tolerance is +/- 5%.

Since the setpoint for this switch is nominally 115 psi (and since 5% of 115 psi is 5.75 psi), a setpoint of 110 psi is in-spec. Sorry!

[Dale]

The weird thing is we've swapped in three switches now and they all read 110. We'll try the gauge next.

[Clifford]

We've run into this problem before as well. We just went along with that switch, but made space for another accumulator to make up the volume difference. One of our regional inspectors said this was the right choice, since modifying the switch in any way could make it illegal for FRC. I would mark the one you modified and set it aside until you can get an answer from FIRST about whether it can still be used.