Abstract: A liquid pump comprises two flexible impulsion members disposed in series between inlet and outlet openings of the pump casing. The members are engageable with sealing means to form an intermediate chamber in the casing between the inlet and outlet. Both members are connected to a common pivot shaft which is rocked to reciprocate the members 180.degree. out of phase in order to drive liquid through the pump. The pivot shaft is sealed from the exterior by torsionally flexible sleeves clamped at opposite ends to the shaft and to the casing.