How Do Piston Diaphragm Pumps Work?

Piston diaphragm pumps are electrically driven positive displacement pumps that operate in a manner similar to an air diaphragm pump. Diaphragms flex back and forth to form a chamber of varying volume that in conjunction with inlet and outlet check balls causes the pump to draw in then expel the slurry being pumped. This makes them ideal for pumping abrasive and thick/viscous slurries with a high concentration of solids such as clays, cement, muck, ore slurries, pigments, latex, acids, lye, pharmaceuticals, and

But how do piston diaphragm pumps work?

An electric motor drives a crankshaft (as in a car) which is connected to a piston. The piston moves back and forth and transmits the stroke via a working fluid to the diaphragm. During the suction stroke the piston is retracting which draws in the diaphragm, creating suction which lifts the inlet check ball and draws the slurry into the diaphragm casing. During the pressure stroke the piston is extending which forces the diaphragm to flex out. This causes the slurry in the diaphragm casing to be forced out through the discharge check ball and into the pressure pipe or discharge piping.

What happens when the pump reaches its maximum pressure?

When the pump is nearing maximum pressure, some of the working fluid is vented through an adjustable relief valve back to the pumps reservoir. This reduces the amount of working fluid that can flex the diaphragm, which also limits how far the diaphragm can be flexed thus reducing the pump flow rate. This also limits the maximum pressure that the pump produces to the desired set point. On the suction stroke the working fluid that was vented is replenished from the reservoir by the make-up valve. Venting and replenishing of the working fluid is what controls the pumps flow and pressure output which keeps energy usage low. The pressure and flow control strategy of venting and refilling the working fluid creates a flow curve that makes a piston diaphragm pump an ideal choice as a filter press feed pump.

Energy Efficient Options

Upon request a hydraulic bypass soft start-up device can be installed. The device switches on when the pump is started in order to reduce energy consumption during startup. The working fluid between the piston and the diaphragm is vented to the make-up tank. The working fluid is automatically replenished by the make-up valve and the flow rate increases to maximum capacity. This soft start-up saves energy and makes the pump economical.

Pump Protection and Safety Features

The flexible diaphragm serves as a barrier between the slurry being pumped and the working fluid. The working fluid is protected from slurry contamination by the diaphragm. This allows the pump to handle abrasive slurries without contamination and wear to the precision internal components. Clean working fluid is necessary to prevent premature wear of precision components such as the piston, relief valve, and fill valve. The diaphragm is usually a two layer design with a pressure sensing port between the layers. A damaged or ruptured diaphragm can be detected by monitoring the sensing port with a pressure switch. The signal from the pressure switch can be wired to the plant control system or motor starter and be used to shut down the pump in the event of a diaphragm failure.

Are you still asking yourself “how do piston diaphragm pumps work?” We have attached a simple animation that represents how a piston diaphragm pump works and may help you to visualize the description above. If you still have questions or would like more information then don’t hesitate to contact us by filling out an application for details form or call us at (770) 592-8664.

David Chittick: