Diaphragm pumps operate as positive displacement pumps through the reciprocating action given through a combination of diaphragms and valves. Moving the diaphragms in and out produces an expansion/contraction cycle. During operation, the suction valve opens and fluid flows in. On the down stroke, the discharge valve opens and liquid flows out.
The reciprocating action creates a vacuum that intakes a set volume of fluid and then pushes it out of the discharge. Given the positive displacement of fluid, the flow rate does not vary and the pumps operate at a continuous discharge rate. In addition, diaphragm pumps contain no sealing or lubricating oils within the pumping head. As a result, the residual gases produced within the vacuum do not contain any oil vapor.
The combination of design, action, and materials has established diaphragm pumps as a good choice for transferring liquids with low, medium or high viscosities and liquids that include large solids. Since the diaphragms consist of different materials, the pumps can also handle corrosive chemicals such as acids. Diaphragm pumps are driven through compressed air, electric motors, magnetic force, and hydraulic power.
A hard diaphragm can generate higher pressures and flows. Softer diaphragms are rated for lower pressures and require less energy to operate.
Flat diaphragms are inexpensive and can provide adequate vacuum separation between chambers but have a limited stroke/offset length, lower energy efficiency, and lower lifespan. It deforms as it adjusts to the stroke.
Rolled/molded diaphragms provide a required stroke length, a repeatable displacement with a constant effective pressure area, and less resistance.
A structured diaphragm incorporates a ribbed underside to accommodate a specific load and provides higher strength, good capacity, and higher efficiency.
Air-Operated Diaphragm Pumps
Air-operated diaphragm pumps (AOD) have become the most popular type of diaphragm pump and use compressed air to drive the diaphragms. AOD pumps have two chambers with a diaphragm, an inlet check valve and an outlet check valve in each chamber. The air supply shifts from one chamber to the other through the action of an air spool valve that resides within the pump. Continually shifting air from one chamber to the other forces liquid out of one chamber and into the discharge piping. As a result, the other chamber fills with liquid.
Electric-Operated Diaphragm Pumps
With electric-operated diaphragm pumps (EOD), electrical energy generated by a small electric motor attached to the pump causes the pumping action of the diaphragm. During operation, a cam system converts circular motion into linear motion and drives the up-and-down plunging motion of the diaphragm. EOD pumps usually have 3/8", 1/2" or 3/4" inlet and outlet ports, and flow rates that range from one to seven GPM. The pumps develop pressures ranging from a minimum of 60 PSI to a maximum of 100 PSI.
Air-operated diaphragm pumps can run dry, can run submerged, and do not require electrical power. The air-driven pumps can self-prime, have variable flow rates, and can handle variable solids.
Applications for AOD pumps range from sewage treatment to chemical processing. Electric-operated diaphragm pumps have many of the same capabilities as air-operated pumps but remain more susceptible to combustion. EOD pumps work well in applications that require smooth and constant dosing.