Fig. 2.
Definition of variables. (A) During valve opening, air is drawn out of the chamber with volume Vo, through resistance Ro, thus decreasing the pressure, p(t), over the valve membrane until the threshold pressure for valve opening, Pto is reached. Q(t) is volumetric flow rate, and I(t) is molecular flow rate at the entrance to the valve chamber. We define I(t) to be positive for flow into the valve chamber and negative for flow out of the chamber. (B) During valve closing, air flows into the chamber with volume Vc, through resistance Rc, until the threshold pressure for valve closing, Ptc, is reached. Vc < Vo because there is less volume in the valve chamber with the membrane deflected.