A diaphragm pump which overcomes the problem of diaphragm failure due to overfill
of the oil transfer chamber and the inability to self-prime. A notch is provided
in the upper portion of the surface of the cylinder so that air can be forced back
to the reservoir. In addition, the bias spring connected to the diaphragm and supported
by the piston is made stiff with a spring constant that produces a bias pressure
that can overcome abnormal suction pressures.
