How Do Air Operated Diaphragm Pumps Work?
As the name implies, air operated double diaphragm pumps (AODD) use compressed air to operate, rather than an electrical motor. This unique operating characteristic allows them to be used in situations where an electrically powered pump would not be advisable (e.g., when pumping flammable liquids). By their very nature, though, these types of pumps must be installed and maintained properly to function as designed.
AODD pumps use a flexible diaphragm mounted on either side of the pump’s central chamber to pump fluids into and out of the pump’s body.
When these diaphragms are pushed away from (or toward) the center section, or air motor, a vacuum is created in the pump’s body, and fluid flows into one of the liquid chambers through an inlet port. When the diaphragms are subsequently pushed in the opposite direction back to their original positions, again via compressed air, the fluid is expelled from the liquid chamber via an outlet port.
This cycle repeats over and over when the pump is in operation, creating the pumping action. Specially designed check valves control the flow of the fluid in and out of the pump’s central chamber as the pump cycles, ensuring that the fluid flows in only one direction.
In Fig. 1 the compressed air has forced the left diaphragm towards the product chamber and displaced the liquid from that chamber through the open valve at the top to the discharge port. Liquid is simultaneously drawn in by the right diaphragm, thus refilling the second liquid chamber. When the end of the stroke is reached, it reverses automatically, and the cycle is repeated in the opposite direction.
In the Fig. 2 liquid is drawn in by the left-hand diaphragm and displaced by the right-hand diaphragm. The liquid is displaced, and thus conveyed, by the compressed air.
What Are Air operated double diaphragm pumps used for?
AODD pumps have good suction lift characteristics, are self-priming in most fluids, and can run dry. These pumps can handle low to medium viscosity fluids with ease (including those containing large suspended solids) and may be used to pump both corrosive and flammable liquids. There’s a saying in the processing industries that if a material can be poured into an AODD pump, these types of pumps can generally pump it.
Due to their simple design, AODD pumps are relatively inexpensive to both purchase and operate, and coupled with their efficiency and accuracy, stainless steel versions are well suited for certain food grade sanitary processing applications, including filling, dispensing, and metering fluids, as well as water removal.
Common uses in the food & beverage processing and biopharmaceutical manufacturing industries include:
- Additive injection
- Sampling
- Dosing
- Coating
- Raw material unloading
- Filling
- Shear-sensitive processes
- Filter presses
- Aseptic transfer of proteins and cells
- Producing the required flow and pressure for spraying and cleaning tasks.
Advantages of Air Operated Double Diaphragm Pumps
- Unlike most other pump designs, AODD pumps can run dry for extended periods of time without damage.
- Due to their air-powered design, AODD pumps are well suited for use in hazardous situations (e.g., in environments where flammable materials are present), as the working mechanisms of these types of pumps don’t produce a spark.
- The pump’s design separates process fluids from potentially sensitive pump parts. The isolation of the pumps internals provide increased time between repair.
- AODD pump diaphragms come in many materials to cover a wide range of temperature and chemical compatibility applications.
- They are manufactured from a wide variety of metal and non-metal materials
- Many AODD pumps are designed for sanitary and food-grade processing.
As with any pump, if the application isn’t right it can be disadvantageous, we suggest you contact an applications specialists to ensure you use the right pump for your unique application.
How to install and troubleshoot AODD pumps
AODD pumps have somewhat specialized requirements when it comes to installation.
- Due to the vibration caused by these types of pumps as the diaphragms cycle, AODD pumps must be mounted on a rigid base plate. Failure to do so will eventually result in the wearing down of the pump’s feet due to friction, resulting in costly repairs.
- The fluid inlet suction pipe or hose must never be smaller in diameter than the size of the suction port. This may cause pump starvation, lowering efficient operations. A 1” suction port, for example, requires a 1” suction hose feeding into it. Also, this suction pipe or hose should be as short as possible, and preferably as close to the supply vessel as possible, provided the total system head does not exceed the pumps duty point.
- The air supply line for these types of pumps must be properly sized. Using too small of an air line leading into the pump will starve it of the “fuel” (i.e., compressed air) required for its operation. If you must supply the pump with a smaller air line, try to supply the pump with an air line no more than one pipe size less than the air supply port. Example; a pump that has a 3/4 inch air supply port should have an air supply line no smaller than 1/2 inch.
- To control the performance (flow and pressure) of an AODD pump, install an air pressure regulator assembly in the pump’s air supply line to control the incoming air pressure. Installing the correct air line size with an air regulator will solve most AODD pump installation problems.
If an AODD pump fails to operate, check for the following:
- Ensure that the air inlet size isn’t too small. As mentioned above, the air supply line inlet pipe should be the same diameter as the pump’s air inlet port. Also, verify that the incoming air pressure is at the required psi to operate the pump.
- Inspect the pump’s muffler for icing. As noted earlier in this article, AODD pumps are loud when in operation, and mufflers are often installed on them as a result. Due to the air compression, these mufflers can operate at temperatures below freezing, and in humid environments icing may occur in the muffler, restricting the pump’s operation.
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To avoid problems with muffler icing, do the following:
- Decrease the air pressure to the pump.
- Increase the pump size, allowing it to operate at lower speeds (i.e., at lower air pressure).
- Exhaust the muffler to a remote location via an exhaust port pipe.
- Add an air line filter with a water catcher and drain.
- Install a heater in the air supply line to the pump.
- Regularly inspect the pump’s surfaces for leakage. Any PTFE O-rings that are fitted to the pump should always be replaced when servicing, as they may be prone to leak on reuse.
- Pump priming on initial start-up may also be a source of problems with AODD pumps. When priming the pump the first time it is used, slow down the pump’s speed initially with an air regulator. When the pump speed has been reduced and the fluid has had enough time to enter the pump’s body, increase the air pressure to operate the pump at its normal speed.
- Check the pump’s inlet and outlet lines for any restrictions, including closed or partially closed valves, and clogs or twists in the lines.
Saniflo™ Hygienic Series
Wilden Saniflo Hygienic Series pumps are capable of efficiently pumping a wide range of fluids found in food processing and biopharmaceutical manufacturing, including sauces and purees, pharmaceutical products and high purity solutions, and abrasive media and solids. They incorporate a free-draining flow path that increases performance and enables CIP capability.
These pumps are offered with passivated stainless steel components for hygienic applications, and are available in multiple sizes and surface finishes.
Saniflo™ FDA Series
Wilden Saniflo FDA Series pumps possess the versatility to safely and efficiently pump a wide range of viscosities and shear-sensitive products. They are available in various materials that meet strict FDA guidelines for sanitary process applications.
FDA Series pumps comply with all FDA, CE, and 1935/2004/EC andrequirements.
Pro-Flo® Shift Series
Wilden Pro-Flo® SHIFT Series pumps provide energy savings and higher flow rates when compared to many competitor pumps. The secret is a first-class design that comes equipped with industry-leading air valves that offer up to 60% energy savings and 34% greater flow rates when compared to other AODD Pump technologies.
Additionally, for increased reliability, the Pro-Flo SHIFT Series has been designed with increased suction lifts and fewer moving parts.
Almatec Pumps
Biocor
Biocor AODD pumpsare suitable for sterile applications within the pharmaceutical, biotechnology, and food processing industries, and are built with compliance to EHEDG and FDA standards.
These pumps feature 316L stainless steel for wetted surfaces, and are engineered with suction and discharge ports that are compatible with Tri-clamp® and other sanitary fittings.
E Series
Almatec’s E Series pumps are the latest generation of plastic AODD pumps, designed for liquid and slurry transfer applications in chemical processing.
All housing bolts in this pump are tightened against a diaphragm-sized ring on either side of the pump’s body, increasing torque loads for greater pump safety. These E Series pumps are designed for low maintenance, with no drives, rotating parts, or shaft seals.
Next Steps
Air operated double diaphragm pumps offer a unique ability to pump a wide range of fluids found in the sanitary processing industries, and are suitable for a variety of applications. In certain situations, such as when pumping flammable liquids, these types of pumps can be the preferred style of pump.
However, AODD pumps require particular attention when it comes to installation and operation.
Having trouble deciding which AODD pump is best for your specific application? Contact CSI at (417) 831-1411. We’ll be happy to assist you in choosing the best pump solution.
ABOUT CSI
Central States Industrial Equipment (CSI) is a leader in distribution of hygienic pipe, valves, fittings, pumps, heat exchangers, and MRO supplies for hygienic industrial processors, with four distribution facilities across the U.S. CSI also provides detail design and execution for hygienic process systems in the food, dairy, beverage, pharmaceutical, biotechnology, and personal care industries. Specializing in process piping, system start-ups, and cleaning systems, CSI leverages technology, intellectual property, and industry expertise to deliver solutions to processing problems. More information can be found at www.csidesigns.com.