Hello,
I am an importer of a small Japanese made air pump, and am consulting with the factory to add an attached alarm to it. The pump is small and inexpensive, so the solution to my problem must also be small and inexpensive. We developed an alarm that would sound in the event of pressure loss, which was easy to do with a pressure switch fed by a 1/8" plastic airline connected with a barb fitting. There is a small market segment that would like to also have the alarm sound in the event of overpressure. Their requirements would be in the range of 4 to 5 psi. I thought we could take the standard alarm unit and add a 1/8 or 1/4" plastic check valve, or something similar. The check valve would lift off its seat at 4 to 5 psi, and the escaping pressure would allow the low pressure alarm to sound. I expect if I could find the correct plastic fitting it would only add perhaps $5.00 to the cost of production. So effectively it would just be a simple Tee with a spring loaded check, but the check valves I find crack at around 0.5 to 1 psi. If I am on the right track perhaps someone could point me to a manufacturer, or if not please correct my thinking and suggest another means to the end.

Thank you!