New member looking for a solution to a problem.

[Bearmtnmartin]

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!

 

[3DDave]

Tricky. An electronic solution would be best but getting the pressure sensor cheaply enough is a problem. There are microprocessors available for 3 cents each, so that part isn't bad; the board and supporting chips might be another 50 cents to a dollar, but no cheap pressure sensors pop up readily.

The mechanical solution might use a simple bellows and a resisting spring with two switches on the bellows. When the bellows passes the first point it opens the 'low-pressure' switch and when it passes/reaches the overpressure position it closes (or opens) the overpressure switch. One might use a plastic Bourdon tube instead of the bellows and save a separate spring.

The overpressure switch could be a metal contact on the bellows or Bourdon tube that closes a circuit; it may not have to be a microswitch as it has only the one endpoint adjustment.

 

[Bearmtnmartin]

Thank you for the suggestion. Unfortunately you hit on the method the only competitor uses, and it is patented in this application! Also, it would require replacing the pressure switch completely on all pumps, or having two different product lines. I am hoping for a simple blow of valve that I could tee into a small diameter line. I have looked at this one:

https://kscdirect.com/item/SPE+S1101-05/Spears_1%2F2+ADJUSTABLE+SPRING+CHECK+VLV+MPTXFPT

I think something like this would work but I need a 1/8 or at the largest, 1/4" version.

 

[JR97]

Put a pressure or flow sensor on the output of the check valve. however, most check valves will re-seat when the over pressure condition passes. You may get intermittent flow / pressure as the check valve lifts and re-seats.