A Hydraulic Diaphragm pump is also a positive displacement pump. This model comprises of hydraulically actuated diaphragm liquid heads incorporating a diaphragm actuated replenishing system. The hydraulically balanced diaphragm pump is a hybrid design. Like the other pumps, its power end and capacity control are common.

This, however, is where the similarity ends, since the plunger does not come in contact with the pumped fluid, and the actuation of the diaphragm is by hydraulic power instead of mechanical power.

The pump consists of three sections which are the drive end, hydraulic chamber end, and the liquid end, also known as the diaphragm head. The drive end mechanism for a plunger pump and hydraulic diaphragm pump is the same. The diaphragm head is fitted to the stroke length control mechanism.

The plunger reciprocates within a precisely sized cylinder at an established stroke length, displacing a volume of hydraulic liquid, not the product liquid. The hydraulic liquid is stable and has excellent lubricating qualities. The plunger uses the hydraulic oil to move the diaphragm forward and backward, causing a displacement which expels the product liquid through the discharge check valve and, on the suction stroke, takes in an equal amount through the suction check valve.

The diaphragm isolates the liquid product being contained within the liquid chamber and check valves. The diaphragm also acts as a perfect seal between the hydraulic oil and the liquid being pumped, creating a hermetically sealed system, making the pump safe for toxic fluids and other hazardous fluids.

When properly installed and working within the recommended temperature range and not affected by corrosion or abrasion, the diaphragm has an unlimited life.