Diaphragm Pumps

A diaphragm pump (also known as a Membrane pump) is a positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic or teflon diaphragm and suitable one-way valves on either side of the pump head  (E.g. check valve, ball valves, flap valve, or any other form of flow operated non-return valve) to pump a fluid.

The reciprocating motion of the diaphragm has a similar effect to that of a piston. The constant flexing of the diaphragm is responsible for the admission of fluid into the pump and subsequent discharge from the delivery end. When the volume of a  chamber increased (the diaphragm moving back), the pressure decreases, and fluid is drawn into the chamber. When the chamber volume decreases (the diaphragm moving forward), the fluid previously drawn in is forced out, completing the cycle. Diaphragm Pumps deliver a hermetic seal between the drive mechanism and the compression chamber, allowing the pump to transfer, compress, and evacuate the medium without a lubricant.

Diaphragm pumps are intended for handling abrasive as well as corrosive fluids and sludges. They are particularly useful for low head applications such as dewatering of trenches and building sites. Small diaphragm pumps can also be suitable for  priming centrifugal pumps.

A diaphragm is used as a versatile dynamic seal that removes many of the limitations found with other sealing methods. They do not leak, offer little friction, and can be constructed for low pressure sensitivity. With the right material consideration, diaphragms can seal over a wide range of pressures and temperatures without needing constant lubrication or maintenance.

There are three main types of diaphragm pumps:

  • Those in which 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.
  • Those employing volumetric positive displacement where the prime mover of the diaphragm is electro-mechanical, working through a crank or geared motor drive, or purely mechanical, such as with a lever or handle. This method flexes the diaphragm through simple mechanical action, and one side of the diaphragm is open to air.
  • Those employing 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.

Grundfos use the first type of diaphragm pump in their chemical dosing pump range. DDE, DDA, DDI, DME and DMX pumps all have the pumped fluid on one side and air on the other. DMH Hydraulic piston diaphragm dosing pumps have the pumped fluid on one side and hydraulic drive oil on the other. Grundfos do not make diaphragm pumps for sludge handling or general transfer of liquids.