Suction & Discharge Sequence of an FTI Air Air Operated Double Diaphragm Pump


Air operated double diaphragm pumps are positive displacement pumps that use a combination of the reciprocating action of two flexible diaphragms, two inlet and two outlet ball check valves to pump a fluid. There are two pump chambers which are divided by the diaphragms into air and fluid regions. The two diaphragms are connected to a common shaft located in the center section. This creates the effect that during a cycle one side is pumping fluid while the other side is filling.



Suction Sequence – Figure 1

Suction Sequence

As the common shaft located in the center section moves to the right, the diaphragm in the left chamber moves towards the center section. This movement creates a vacuum on the liquid side of the left diaphragm, lifting the lower ball check valve, allowing liquid to flow through the suction manifold into the liquid chamber. At the same time, any fluid in the right chamber is discharged.

Discharge Sequence – Figure 2

Discharge Sequence

The air distribution system senses that the diaphragm in the right chamber reaches the end of its discharge stroke and causes the common shaft to shift. This moves the diaphragm to the left pressurizing the liquid, lifting the upper ball check valve, allowing fluid to flow though the discharge manifold and out of the pump.


Annotated GIF 4 - Timing