What is a diaphragm pump? Also known as a Membrane pump that uses a combination of the reciprocating action of a rubber, thermoplastic or PTFE and suitable valves on either side of the body (check valve, butterfly valves, flap valves, or any other form of shut-off valves) to pump a fluid.
There are three main types of diaphragm pump. Those in which the pump 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 sections with the fluid to be pumped on both sides. The diaphragm(s) again are flexed, causing the volume to change.
When the volume of a chamber of either type of pump is increased, the pressure decreases, and fluid is drawn into the chamber. When the chamber pressure later increases from decreased volume, the fluid previously drawn in is forced out. 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 an internal combustion engine. 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.
An elastomeric membrain can be 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, Yamada pumps can seal over a wide range of pressures and temperatures without needing lubrication or maintenance.
A double diaphragm is a positive displacement pump which utilises two flexible diaphragms that reciprocate back and forth, creating a temporary chamber, which both draws in and expels fluid through the pump. The diaphragms work as a separation wall between the air and the liquid.
The first stroke
The two diaphragms that are connected by a shaft through the centre section where the air valve is located. The purpose of the air valve is to direct the compressed air to the back of diaphragm number one causing it to move away from the centre section. The number one diaphragm causes a press stroke moving liquid out of the pump. At the same time diaphragm number two is performing a suction stroke. The air behind diaphragm number two is being pushed out to the atmosphere causing atmospheric pressure to push the liquid to the suction side. The suction ball valve is pushed away off its seat allowing the fluid to flow past the ball valve into the liquid chamber.
The second stroke
When the pressurised diaphragm number one has reached the end of its stroke, the movement of the air is switched from diaphragm number one to the back of diaphragm number two by the air valve. The compressed air pushes diaphragm number two away from the centre block resulting in diaphragm number one being pulled toward the centre block. In pump chamber number two the discharge ball valve is pushed off its seat, whilst in pump chamber number one the opposite occurs. Upon completion of the stroke the air valve leads the air again to the back of diaphragm number one and restarts the cycle.
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