Membrane-air pump adapted to function as a tachometer

Claim 1

In a positive displacement pump, a first flow circuit extending from a flow inlet at the suction side of the pump to a discharge at the delivery side of the pump providing flow or pressure values serving a speed-dependent guide values for control or regulating apparatus, said first flow circuit including a pump chamber; a flexible membrane dividing said pump chamber into first and second chamber portions sealed from each other; a first suction chamber communicating said first chamber portion with said flow inlet; a first pressure chamber communicating said first chamber portion with said pump discharge, a second suction chamber communicating said second chamber portion with said flow inlet; and a second pressure chamber communicating said second chamber portion with said pump discharge, the improvement comprising: a second flow circuit extending from said first pressure chamber upstream of said pump discharge to said first suction chamber; relief pressure valve means in said second flow circuit inhibiting flow therethrough below a predetermined low flow or pressure value at said pump discharge and permitting return flow therethrough from said first pressure chamber to said first suction chamber at and above said predetermined value; and adjustable throttle means in said second flow circuit located intermediate said relief pressure valve means and said first suction chamber and operable above said predetermined low flow or pressure for adjustably restricting the flow through said second flow circuit and controlling the flow or pressure values at said pump discharge.