How does a diaphragm pump work

AODD pumps (Air Operated Double Diaphragm) are alternating double diaphragm volumetric pumps that use compressed air as motor fluid.

COMPONENTS

There are three main sections in the construction of AODD pumps:

• Central casing: includes the air inlet and outlet and the pneumatic exchanger;
• Fluid chamber: houses the volumes in which the fluid is aspirated and pumped, including the diaphragms (green and yellow in the image below). Sometimes they include the ball seats (that work similarly to a check valve in inlet and outlet).
• Manifolds: used as the connection interface with the system. Sometimes they include the ball seats (that work similarly to a check valve in inlet and outlet).

AODD pump cross section

The various components can have different layouts, whilst maintaining the same operating principle, according to the size of the pump and their series.

OPERATION

As mentioned earlier the entire operating cycle of an AODD pump is based on using compressed air as motor fluid.

Air cycle

As shown in the adjacent figure, the air enters the central casing through an opening, and after driven the pump inside the pneumatic exchanger, comes out.

During this passage the air undergoes a sudden expansion that lowers the temperature at the outlet, creating the conditions for forming ice, whenever the supply air has not been adequately dried and filtered.

A key element to the operation of the pump is the pneumatic exchanger (Debem patent).

It consists of the following:

• an external cylinder, divided into three sections; the air enters the central one and exits from the lateral ones;
• a shuttle that, by moving along the axis, sends the air alternatively to the two diaphragms;
• a shaft on which the shuttle slides and onto which the diaphragms are secured.

Pneumatic exchanger

EXCHANGE CYCLE

The exchange cycle essentially consists of three phases that are repeated alternatively for each chamber.

PHASE 1

Exchanger phase 1

The air, passing through the opening in the pump casing, reaches the central ring where, through a series of passages between the spool and external ring, it reaches one of the two antechambers (in the figure the path is highlighted in red and the antechamber in blue).
The diaphragm, pushed by the air pressure, pushes the liquid into the manifold. The correct direction is ensured by balls below that, due to the effect of gravity, close the passage, preventing the liquid from falling.

PHASE 2
In the second phase the spool, pushed by the air, strikes the opposite side of the pneumatic exchanger, sliding along the shaft and pressurises the other antechamber.

Exchanger phase 3

PHASE 3

The third and final phase is the discharge.
The antechamber of the diaphragm, which was pressurised previously, now has an open passage to the outside: the traction of the opposite diaphragm, which is now inflating, retracts the diaphragm and creates a vacuum in the fluid chamber, which allows the fluid to rise and fill it.

At the same time the phase 1 is repeated for the second chamber and the cycle restarts.
The range of supply pressures supported by most Debem pumps is between 2 bar (minimum) and 8 bar (maximum), even though we have tested that even pressured under 1 bar are sufficient to operate certain models.