Eccentric screw pump with liquid bypass controlled by a flexible diaphragm

An eccentric screw pump for delivery of gas and/or liquid, comprising:

• a pump casing having an intake inlet and a delivery outlet and forming a suction chamber and delivery chamber;
• delivery elements disposed within said pump casing adapted to be driven by a motor, including a casing insert forming a stator and an eccentric screw rotatable within said stator;
• a liquid bypass line connecting said suction chamber and delivery chamber;
• a valve provided in said liquid bypass line;
• and
• a control element for opening and closing said valve, said control element being a flexible diaphragm which is actuated on the basis of a pressure differential between said suction chamber and delivery chamber, such that during delivery of at least a predetermined proportion of gas said valve is set in an open position and during delivery of liquid said valve is set in a closed position.