In brief
A diaphragm pump is a positive displacement pump in which an oscillating diaphragm separates the pumped medium from the drive and draws it in and expels it via valves.
Contents
What is Diaphragm pump?
The diaphragm moves back and forth, enlarging and reducing a pumping chamber. Check valves on the suction and discharge sides determine the direction of flow. Because no shaft seal comes into contact with the medium, diaphragm pumps are suitable for aggressive, toxic, abrasive or solids-laden liquids in chemicals, electroplating, food production and wastewater treatment.
Air-operated double diaphragm pumps are widespread: they need no electric motor, can run dry safely and can be controlled via the air pressure. Mechanically or hydraulically driven diaphragm pumps work with a motor and eccentric and are also used as metering pumps. Key parameters are flow rate, discharge pressure, suction lift, connection size and the materials of the housing, diaphragms and valves, such as polypropylene, stainless steel, PTFE or EPDM.
Diaphragms are wear parts that fatigue as a result of load cycles, chemicals or solids. A ruptured diaphragm can allow the medium into the air side or the drive, so regular inspection and spare part kits make sense. For pumps available in several material variants, the spare parts order must match the installed version exactly. A wrongly selected diaphragm can swell or tear and quickly lead to another failure.
In practice: maintenance and procurement
Replacement diaphragms and valves require the pump type, size and material combination from the type designation. For new media, the chemical resistance of the materials should be checked before use.
Synonyms and abbreviations: double diaphragm pump · AODD pump (air-operated double diaphragm) · air-operated diaphragm pump · membrane pump
Frequently asked questions
How does an air-operated double diaphragm pump work?
Two diaphragms are connected by a rod. An air control valve alternately pressurises the back of one diaphragm with compressed air, which pushes the medium out of its chamber while the opposite diaphragm draws medium in. Ball or flap valves determine the direction. The flow rate can be adjusted via air pressure and air volume.
What information is needed for diaphragm pump spare parts?
Required are the pump type and size, drive type and the materials of the housing, diaphragms, valve balls and valve seats. This information is usually encoded in the type designation. The serial number should be to hand for diaphragm kits. If the medium changes, the resistance of the materials must be checked.
Can a diaphragm pump run dry?
Air-operated double diaphragm pumps are considered safe to run dry because there are no sliding seals or rotating parts rubbing in the medium. Prolonged dry running nevertheless increases wear on diaphragms and valves. For other designs, the manufacturer’s specifications apply. The valves should also be checked after periods of dry running.
When is a diaphragm pump better than a centrifugal pump?
Diaphragm pumps are advantageous for viscous, abrasive or solids-laden media, for aggressive chemicals without the risk of leakage at shaft seals, for self-priming operation and, with an air drive, in potentially explosive atmospheres. Centrifugal pumps are usually more efficient for large volumes of low-viscosity media and continuous operation.