A DIY pressureswitch
Ever heard of a "vacuum advance unit"? It's a small device used in car engines.
Has something to do with the ignition moment. It is a small "can", equipped with a membrane attached to a lever. It has a tubeconnector at the side opposed to the lever. See also the picture. It can be used to make a pressureswitch yourself. Here is what I did:
I connected the vacadvance to some copper piping built in a wooden box. The vacuum pulled by my pump is applied on the unit and therefore it retracts the lever. The lever in its turn operates a switch. (See the second picture) The whole contraption can be tuned by tightening a spring.
To get some feedback I mounted the pressuregauge on top of the box.
See the third picture for the end result. It works like a charm!.....
However.... The switch has a wide range of "hysteresis". In this case it means that the points at which the switch kicks in and out are a bit too far apart. On operation the pressureswitch switches the pump off at let us say -0.9bar. It switches on again at -0.7bar. Rather wide apart.
It will do for the time being, but when another solution comes by I will give it a serious consideration.