Air-operated double diaphragm pump is a very common type of diaphragm pump. As its name suggest, the pump operation is carried out using compressed air, rather than electricity. The air operated double diaphragm pump is made up of the two liquid chambers and two membranes/diaphragms. Each of the chambers has a discharged and suction check valve. Basically, the pump uses the two diaphragms to pump liquids in and out of the pump’s body. The flow of air flow of air between the chambers is controlled through and inbuilt air spool control device. The flow of air from one membrane to another causes one chamber to expel fluid through the discharge and also facilitates the suction of fluid in the other chamber. Due to their unique operation characteristics, air operated double diaphragm pumps are suitable for applications where the use of electricity would be disastrous e.g., pumping of flammable liquids.
Fig: The components of an air operated double diaphragm pump (image credits: michael-smith-engineers.co.uk)
The air operated double diaphragm pump uses specially designed check valves to control the flow of fluid in and out of the central chamber during pump operation. The function of the check valve is to ensure the fluid flows in one direction only.
Working principle of air operated double diaphragm pump
The compressed air distribution system directs air to the back of diaphragm A pushing it away from the center section. The diaphragm A then causes a press stroke on the liquid chamber expelling the liquid out of the chamber A. At the same time, the compressed air behind the chamber B is pushed out into the atmosphere and a vacuum is created. The inlet ball valve in chamber B is forced out of its seat allowing the chamber to be filled with liquid. Once the pressurized diaphragm A has reached the end of its stroke, the air in the chamber is vented out by the air distribution system and compressed air is directed behind the diaphragm B. The compressed air pushes diaphragm B away from the center of the pump body resulting in the shaft pulling the diaphragm A towards the center of the pump body. Simultaneously, the volume of chamber B decrease, the discharge ball valve is pushed off its seats, and the fluid is pumped into the discharge port. Upon completion of the stroke the air valve leads the air again to the back of diaphragm A and restarts the cycle.
Figure: suction and discharge cycle of air operated double diaphragm pump.
Characteristic of Air operated double diaphragm pump
- It is a positive displacement type of pump
- The air operated double diaphragm pumps are leak-free
- Can handle high viscosity fluids
- It is suited for the transfer flammable, toxic and corrosive liquids
- Air operated double diaphragm pump can achieve maximum efficiency of about 97%
- has excellent self-priming ability
- internal components are suspended in oil to reduce wear and to extend service life
- Great idling properties
- it can be used to create artificial heart
- suitable for exhaust pressure of up to 1200 bars
- Good suction lift properties: low flow rate and low pressure
- Gentle spinning and thus suitable for shear sensitive media
- Air operated double diaphragm pump can operate in submerged conditions
Application of air operated double diagram pump
Air operated double diaphragm pump pumps are extensively used in various industries for wide range of purposes as highlighted below
Biopharmaceutical manufacturing, food and beverage industries
- Air operated double diaphragm pump are used in injection of additive
- chemical dosing
- To transfer corrosive, abrasive and toxic chemicals
- unloading raw material
- Aseptic transfer of proteins and cells
- Air operated double diaphragm pump shear-sensitive processes
- Filter presses
- To produce the required flow and pressure for spraying and cleaning tasks.
- loading and unloading tankers, totes and barrels
Waste water treatment plants
- Transferring solid lade media
- Air operated double diaphragm pumps are used as utility pumps
Oils and gas
- oil and glycol transfer
- settling pond transfer
- filter presses
- Dewatering sites and quarries
- pumping abrasive slurries and sludge mixtures
- Transferring solvents for separating minerals from ore
- moving fuels for vehicles and equipment
Electroplating and anodizing
- Air operated double diaphragm pump replenishing chemicals in plating and metal finishing tanks
- Offloading corrosive as well as solid laden waste
- Agitating cleaning solutions
- Circulating liquid to avoid sedimentation
- Filtration (when critical purification is required for high quality parts)
Advantages of air operated double diagram pump
- Can run dry-unlike conventional pump an air operated pump can run dry for a long time without damage or any operational issues. This is because the pumps have no internal seals or moving parts that require lubrication. Conventional pumps such as the lobe pump, magnetic drive pumps, centrifugal pump would have to stay primed during operation to prevent damage to some of their components, which can lead to expensive repairs.
- Safety- The pump can be used for flammable liquid because they are air powered and cannot produce spark. Also suitable for volatile chemicals
- The pump requires minimal repairs- The pumping fluid is separated from sensitive pump components; hence increased time between repairs
- Application versatility- the pump and the diaphragms are made from a variety of material enabling the pump to have a wide range of applications. They area also capable of handling variety of feeds ranging from low viscosity to high viscosity fluids.
- Can be used for sanitary and food grading processes
- Simplicity- the pump design does not involve complex wiring or electrical controls. This makes the pump easy to install and operate
- Does not require electricity
- Suitable for corrosive, abrasive and powdered materials
- relative low cost and reliable
Disadvantages of air operated double diagram pump
- The efficiency of AODD depend on the quality of compressed air.
The pressure of compressed air must be higher than the pressure of the fluid to be pumped.
- The pump is prone to icing.
This may occur due to constant venting which can cause ice to build up around the air vent or within the air distribution system. This challenge can be solved by installing a heater or maintaining the pressure of compressed air at the level recommended in the pump manufacture’s guide
- AODD produces a pulsating discharge
This is caused by the cycling action of the diaphragm which cause the fluid to accelerate during compression cycle and to slow down during the suction cycle, creating pulses in the discharge. To solve this problem, a dampener must be installed on the top of the pump to decrease the pulses.
- The pump can be noisy
Noise in AODD pump is caused by the constant venting of the air valves and vibrations resulting from the cyclic action of the diaphragm and. The level of noised can be reduced by installing the air vent line with a muffler.
Troubleshooting Air operated double diaphragm pump
Air operated double diaphragm pump fails to operate
- air inlet size too small (replace with large airline)
- Icing in the pump muffler (install a heater in the air supply line of the pump, decrease pump’s air pressure, lower the pump speed, install air line filter)
- Leakage on the pump surface (check for ant worn our O-rings and replace)
- Ball valve wedged into seat due to excessive pressure (install pressure relief valve)
- Dispensing valve is clogged (Reduce pressure and clear the valves)
- Blocked air connection
- Diaphragm breakdown (replace the diaphragm)
- Dirt in the pump chamber (clean dirt from the chambers)
Air operated double diaphragm pump cycles but does not prime
- clogged inlet or outlet (clean)
- Pump speed too high leading to cavitation before priming (reduce the inlet pressure of air)
- lost inlet fittings or manifolds (Tighten)
- Check valves balls severely worn out (replace the balls)
- Closed or partially closed valves (ensure suction and discharge valves are open)
Air operated double diaphragm pump has premature diaphragm failure
- Excessive pressure on the suction side (raise the pump or place it on top of the tank to reduce pressure
- Cavitation (Enlarge pipe diameter on the suction side of the pump or move closer to the product)
- Wrong selection of materials
- long periods of dry running
- Incorrect diaphragm plates or plates installed backward (consult manufacturers guide on correct installation)
- Startup with too high pressure on the suction side (start the pump at the pressure level as recommended by the AODD pump manufacturers)
Air operated double diaphragm pump has Liquid leaking
- loose side housing (tighten the tire rods, screws)
- Damaged O-rings on manifolds (check and replace)
- fault in the pipe network
- Ruptured diaphragm (replace the diaphragm and ensure regular maintenance to prevent this from occurring)
Air operated double diaphragm pump has bad flow or pressure
- Pressure falls in air supply or Pressure losses on suction side air supply
- air valve leaking
- worn our Valve balls or Valve seats (check/repair/replace the valves)
- Air in the liquid
- Icing on the muffler
Air operated double diaphragm pump has unequal cycling
- Excessive suction lift (fill the chambers with liquid to prime the pump)
- pumped fluid in the exhaust air muffler
- Air leakage on the suction side
- Obstructed check valves (dislodge the obstruction in the check valve pocket)
- Entrained air or vapor lock in the chamber (use chamber vent plugs to purge chambers)
This article discusses the air operated double diaphragm pump, the operation mechanism, and applications. It also explores the benefits, limitations, and troubleshooting issues related to the pump. An air operated double diaphragm has been defined as a type of diaphragm pump that is powered using compressed air. The air operated double diaphragm pump consists of two liquid chambers and two membranes through which it sucks in and expels liquid from the pump. The flow of compressed air between the pump membranes is managed by an in-built air distribution system while the flow of air in and out of the pump is regulated through specially designed check valves.
An air-operated double diaphragm pump is characterized by a cyclic operation, gentle spinning and self-priming ability. The air operated double diaphragm pumps are widely used to transfer viscous, corrosive and abrasive liquid in different industries such mining, oil and gas, food and beverage, and waste water treatment plants, and pharmaceuticals industries. As the AODD pumps run on compressed air, they are suitable for applications where the use of electricity would be disastrous e.g., pumping of flammable liquids, highly volatile liquids and hazardous environment.
Air operated double diaphragm pumps offer a myriad of benefits including the ability to run dry without damage, they are self-priming, simple construction, ease of installation and minimal maintenance requirements. These pumps are also available in different designs to suit the needs of different applications. However, these pumps also have a few operational limitations including icing in the pump muffler, pulsating discharge, noisy operation, and their efficiency is dependent on the air quality. Some of the common troubleshooting issues for an air operated pump include unbalanced cycling, premature diaphragm failure, pump cycling but not priming, bad flow and press and many more.