How do piston diaphragm pumps work?

Wobbly plate

The shaft drives a wobble plate, which converts the rotary motion of the shaft into an oscillating motion. This oscillation deflects the hydraulic pistons and the suction stroke fills the pistons with oil. The oil is pre-pumped towards the back of the diaphragm during the discharge stroke. This pressure is almost identical to the pressure on the medium side (= hydraulically balanced diaphragm).

During the suction stroke, springs in the hydraulic piston help to return the diaphragm to its original position. While the diaphragm is in the suction stroke, the medium flows through the open suction valve in the diaphragm chamber. The discharge pressure valve is closed in the suction stroke. During the discharge stroke the discharge pressure valve opens, the suction valve closes. This generates the pumping motion.


The crankshaft is held in position by a respective ball bearing at the ends of the shaft. Between these bearings, pistons are attached to one or three cams. These pistons are attached at the other end to a spring-loaded check valve. The complete mechanism is immersed in a lubricating oil bath.

As the drive shaft rotates, each cam actuates the associated piston. Thus, the axial movement is converted into a linear pumping motion of the diaphragm attached to the piston. Each piston is located in a separate oil chamber that equalizes the pressure of the oil behind the diaphragm to the media-side pressure.

During the discharge stroke of the piston, the oil is compressed, causing the respective membrane to move outward and push the liquid out of the pump head. As the diaphragms move back, the liquid is admitted to the suction side of the pump head. The pistons are driven sequentially in uniform sequences by the drive shaft. This leads to a superposition of the strokes and thus to a uniform, nearly pulsation-free flow.

Asynchronous design

The principle of asynchronous design is the same principle as the crankshaft principle. But the diaphragms are not mechanically attached to the pistons. The diaphragms are hydraulically controlled. This allows much more performance with less mechanical stress. The underflow or overflow valve keeps the diaphragm in hydraulic equilibrium.

During the discharge stroke of the piston, the oil in the valve chamber is compressed at the diaphragm and leads to a deflection of the diaphragm. This controls the pumping action. This system eliminates the environmental concerns of packaged piston pumps and provides a virtually pulsation-free, linear flow - without the need for a pulsation damper.

Contact me about my application

Have you got any questions regarding your application for our pump expert? Do you want to know how pumps can help your process? Leave your contact details and one of our pump experts will contact you!