A reciprocating positive displacement pumping system has a rigid chamber wall (31) to which a flexible membrane (33) is attached defining a pumping chamber. An inlet (34) and outlet (37) allow liquid flow. A rigid limit structure (32)limits the movement of the membrane and the maximum volume of the pumping chamber defining an actuation chamber. An actuation port (38) through which a fluid under positive or negative pressure can communicate with the actuation chamber is configured to connect to a positive pressure fluid reservoir and a negative pressure fluid reservoir through a valving mechanism for controlling the flow of control fluid between the actuation chamber and each of the reservoirs. An actuation chamber pressure transducer (44) measures the pressure of the actuation chamber and a controller (49) integrates pressure information from the actuation chamber pressure transducer over time during a stroke to detect an aberrant liquid flow condition.
