Pneumatic Pressure Switch

We used RS Stock no. 398-7045 (£15) for Blue with a mosfet switch instead of a relay, but found out the hard way that they bounce. They are only made of a spring and set of contacts that the spring closes (or opens) when it gets to the set pressure. When near the set pressure any shocks cause the contacts to bounce. Hence when they reach pressure they will turn on and off several times very quickly. This was enough to burn out the motors on the cheap compressors alone. Also trying to start the motors while pressurised at 10 bar also overloaded the motors.

The solution for us was actaully quite simple. Use a time delay, so if it fires it turns off for 5 seconds or so before allowing it to turn on again. This can be done by adding one resistor and capacitor so its not that hard.

In the end we found a large compressor as the cheap ones were not reliable enough for us and we wanted more flow rate as always. They are a good starting point for someone who wants to use pnumatics, thats how we started, and as long as you dont push them too hard they will last a while but they are cheap for a reason.