A special pump is the EM type pump. It is an electric driven, single-diaphragm pump. The diaphragm, made from an elastomer, covers the pump chamber and is forced up and down by means of an excenter, driven by an electric motor-reductor combination. Check valves in the inlet and outlet allow the fluid to move in one direction only.
Due to the large inlet and outlet ports and clearance between diaphragm and pump housing, debris and particles can easily pass through the pump without causing any damage. It makes the pump ideal for media which, in addition to oil, contain a lot of other pollution. It reduces maintenance to replacing the diaphragm 3 to 4 times a year, an inexpensive component which is easily replaced, keeping maintenance cost very low. The heavy, bronze, pump housing is very durable, making the pump suitable for use in virtually any environment.
The pump is not suitable for applications that require a high differential pressure. The maximum allowable suction height is less than 1 meter and the discharge height (pressure) should not be more than 5 meter (0,5 bar). The pump is self-sealing in the counter-flow direction only which means it can not be used in situation where the liquid level on the suction side is considerably higher than the level on the discharge side, unless special measures are taken.