Diaphragm Pump

Written by Matt Milbury. Posted in Pump

A diaphragm pump, also known as a membrane pump, is a positive displacement pump that uses a combination of the reciprocating action of a diaphragm and a series of check valves to pump a fluid. The action of a diaphragm pump is similar to that of a piston pump in which the piston is replaced by a pulsating flexible diaphragm. This removes the piston and packing from the process fluids. Therefore, they are useful in processes where leaks through packing cannot be tolerated.

The process starts when the diaphragm flexes and increases the volume in the pump chamber. The differences in pressure, cause the fluid to rush in. The diaphragm flexes and decreases the volume in the chamber. The fluid is forced through the discharge by a check valve. Finally, the diaphragm moving up once again draws fluid into the chamber, completing the cycle. This action is similar to that of the cylinder in a piston pump.

The materials for a diaphragm pump must be chosen to suit the process. Typical materials are Buna-N (Nitrile), EDPM, Neoprene, Polyester, Polyurethane, Rubber, Polytetrafluorethylene (PTFE). Note that these materials are all sensitive to heat and should not be used in high temperature applications. In applications where sludge, sewage, or other suspended solids are parts of the consistency of the media, a strainer can be used to protect the pump from debris that can clog or interfere with the pump operation.

Diaphragm pumps can be run dry for an extended period of time so they can be used in many automotive, water, food and beverage, and marine applications where continuous use is required.

Types

  • The diaphragm is sealed with one side in the fluid to be pumped, and the other in air or hydraulic fluid. The diaphragm is flexed, causing the volume of the pump chamber to increase and decrease. A pair of non-return check valves prevent reverse flow of the fluid. This is known as a single acting diaphragm pump.
  • Anther type of diaphragm pump acts the same as the one listed above with the exception that the diaphragm is moved by a mechanical crank or geared motor. This type of pump method flexes the diaphragm through simple mechanical action, and one side of the diaphragm is open to air.
  • The third type of diaphragm pump has one or more unsealed diaphragms with the fluid to be pumped on both sides. The diaphragm(s) again are flexed, causing the volume to change.

Applications

  • Sludges and Slurries & viscous liquids
  • Mining
  • Pulp and Paper
  • Petrochemical
  • Automobile Fuel Pumps
  • Artificial Hearts

Characteristics

  • Can be run dry
  • Low shear pumps
  • Good suction lift characteristics
  • Self Priming
  • Good rangeability, depending on the diaphragm diameter and stroke length

Failure

  • Cause a pulsating flow that may cause water hammer
  • Diaphragm may wear or tear if not suitable for the process.
  • Diaphragm may tear or burst if pressures are exceeded.