An air-operated double diaphragm pump (positive displacement pump or reciprocating pump) may be simple in design but that doesn’t stop it from operating across challenging environments. These mechanical pumps are appropriate for on-off cycling, continuous, and on-demand intermittent requirements.
In this blog, we will discuss the following points:
- Definition of AODD pumps
- Features and benefits
- Working principle
- Basic components of AODD pumps
What Are Air-Operated Double-Diaphragm Pumps?
Air-operated double diaphragm pumps (AODD pumps) are positive displacement pumps with two pumping chambers. Flexible diaphragms alternatively fill and discharge the two chambers. Air chambers on the other side alternatively fill and vent compressed air supply to create a pumping action.
AODD pumps are used in transfer applications and can handle a wide range of feeds, including slurries, sludge, and shear-sensitive and abrasive fluids. The pumps are reliable, robust, and easy to maintain. That said, they can be noisy, limited to low-pressure applications, and prone to icing.
Features and Benefits
The features and benefits of air-operated double diaphragm pumps include:
- The simple design of AODD pumps makes them easy to use. They don't have any close-fit, sliding, or rotating parts and thus, require minimal assembly. Once you connect the AODD pump to a compressed air supply, they are ready to run.
- AODD pumps can run dry without damaging the parts or destroying the motor. They don't use any lubricants or oils making them free of clogging due to lack of lubrication. The pumps don't require any cooling mechanism.
- You can program the system to shut down once it has reached certain pressure without damaging the pump.
- Air-operated diaphragm pumps are lightweight and portable, which makes them easy to use in diverse locations. They are easy to dismantle, repair, clean, and maintain.
- You can use AODD pumps for diverse mediums such as water, effluent, harsh chemicals, naphtha, and animal entrails. They can handle water, 90% solids, and everything in between.
- The pumps are customizable and can meet your application requirements, keeping costs to a minimum.
- AODD pumps operate on the compressed air supply. They don't require a power source or fuel to run. This eliminates any harmful exhaust, short circuits, and liquid spilling on live wires thus keeping the surroundings and workers safe.
- They are fully sealed and you can submerge them in any liquid safely. The pumps are suitable for the food and beverage industry because they are not a contamination risk.
- The pump comes in different sizes and flow rates. It can pump as slowly as 1-gallon per minute.
- Double diaphragm pumps are easy to maintain. They don't leak unless both the diaphragms fail. The internal ball valves provide a better seal and are less prone to wear than flap valves.
The limitations of compressed air pumps include:
- The efficiency of the AODD pump depends on the compressed air supply. The pressure should be either equal to or higher than the pumped fluid. This makes the pumps suitable for low-pressure applications.
- The pump speed depends on the supply of air and fluid. An increase in the compressed air pressure or reduction in the fluid pressure can increase the pumping speed. Additional flow and pressure control may be needed to maintain a constant flow.
- The AODD pump draws power and control from an air distribution system which is relatively cheap, simple, and easy to maintain. However, some applications may need to filter expelled air to capture contaminants.
- Poorly designed AODD pumps can constantly vent air, causing icing problems. You can minimize this by avoiding constrictions, reducing the humidity and pressure of compressed air, or installing a heater.
- The cyclic action of the diaphragms creates a pulsating discharge. The fluid accelerates during the compression and slows down during suction. You can use the pulsation dampeners in discharge piping to reduce vibrations, loosened connections, and leakage.
- AODD pumps can be noisy because of the vibrations and the constant venting of the air valves. You can reduce this noise by fitting a muffler on the air vent line.
AODD pumps have applications in metering, dispensing, transferring, and dosing applications.
Mining – The pump can operate in hazardous areas.
- Dewatering above and below ground and in quarries.
- Transferring sludge mixtures and abrasive slurries.
- Dosing reagents.
- Transferring solvents used in separating minerals from the ore.
- Transferring fuel for equipment and automobiles.
Coatings – The pump can work with low to highly viscous liquids and low shear/gentle fluid transfer.
- Dispensing, dosing, and transferring paint, dyes, and ink.
- Feed pump for spray guns.
- Flush/clean paint lines using solvents.
Ceramics – The pump can work with abrasive slurries.
- Day tank transfer.
- Ceramic slips.
- Filling molds.
- Circulating ceramic slurry.
- Wastewater transfer.
Chemicals – The pump has high resistance to corrosive/hazardous chemicals.
- Loading and unloading the tankers, barrels, and totes.
- Portable utility pump.
- Batching/dosing chemicals.
Anodizing and electroplating
- Replenishing chemicals in metal finishing and plating tanks.
- Agitation of cleaning solutions.
- Circulation of liquid to avoid sedimentation.
- Filtration for critical purification of high-quality parts.
- Offloading solid-laden and corrosive waste.
Pulp and paper
- Printing inks.
- Bulk transfer.
- Kaolin clay.
Oil and gas – The pump can operate in hazardous areas.
- Settling pond transfer.
- Oil and glycol transfer.
- Filter press.
- Bulk transfer.
- Transferring solid-laden media.
- Filter press.
- Utility pump.
How Does an Air-Operated Double Diaphragm Pump (AODD Pump) Work?
Air-operated double diaphragm pumps function by displacing fluid from one of the two liquid chambers on each stroke. AODD pumps require a certain amount of pressure and air volume to deliver the fluid.
The two diaphragms are connected through a linked shaft, two inlet valve balls, and two outlet valve balls. The diaphragm acts as a membrane for separating liquid and compressed air supply.
Driving the diaphragms with compressed air pressure instead of the shaft balances the load and removes the mechanical stress. This allows the valve balls to open and close on the valve seats and direct the liquid flow.
Air-Operated Double Diaphragm Pump Mechanisms
The compressed air in an AODD pump enters an air motor. The air motor directs the air to push a diaphragm, pushing the liquid out. Another diaphragm attached to the first one is pulled, creating a cavity on the other side, refilling the second liquid chamber.
On the top and bottom of the two diaphragms are one-way valves (ball valves or flap valves). When a cavity closes, it pushes the liquid up and out. On the other side, it opens another cavity to suck the liquid inside. This can happen at up to 400 cycles per minute.
What Are the Basic Components of an Air-Operated Double Diaphragm Pump (AODD Pump)?
The information below explains each of the components in brief.
Fluid Side Components
The Fluid Suction/Discharge Manifold
The manifold seals and creates a flow path for the liquid. It is bolted or clamped to the outer chambers. The valve/seat seals between the outer fluid chamber and the manifolds are leak-free. They also have the valve balls in the ball cages inside the manifold.
The Outer Fluid Chamber
The outer fluid chamber is a part of the pump's fluid path. It is sealed and attached to the discharge and suction manifolds by the seats. It is also sealed with the diaphragm's bead between the air chamber. It creates an empty space for the reciprocating diaphragms to draw fluid in and push it out on each side to start pumping.
Diaphragms act as a barrier between the fluid side and the air side of the pump. They maintain a seal at the center of the diaphragm hole by tightening the inner and outer plates to the main shaft. The outer circumference is also sealed.
The Inner/Outer Diaphragm Plates
The plates work in combination with the diaphragms to isolate the fluids from the air. The plates are fastened to the diaphragm rod by threading, to compress the diaphragms and create an air-tight and fluid-tight seal.
Clamp Assemblies or Bolts
The pumps are available in clamped or bolted styles. Clamp assemblies or bolts are used to assemble the pump components.
Air Side Components
The Main Shaft/Diaphragm Connecting Rod
The diaphragm connecting rod or main shaft connects the assemblies. They can be either male or female-threaded to connect to the external plates.
The Inner Chamber/Air Chamber
The inner chamber holds the seal with the diaphragm when compressed air enters alternatingly. This pressurizes the rear of the diaphragms, which in turn puts pressure on the fluid.
The Air Valve
The air valve directs compressed air into the air chambers and shifts the diaphragm/connecting rod assembly.
The Intermediate/Center Block
The center block guides the main shaft with seals and bushings. The pilot shaft delivers alternating pressure on the air valve to shift the main valve spool, creating a reciprocating action within the pump.
Air Exhaust Muffler
The air exhaust muffler reduces the sound of the air from the pump. You can remove the muffler and port the exhaust. This allows you to submerge the pump or release the air to any other safer place.
Important Pump Component Considerations
The following components can significantly impact the pump's performance and mean time between failures.
The Valve Balls
Use heavy-weight valve balls while pumping viscous fluids. It will allow them to cut through the liquid and seat faster under gravity. This makes pumping with thick fluids efficient.
The Valve Seats
If you are pumping abrasive fluids, use abrasive-resistant valve seats. For example, stainless steel valve seats are suitable for abrasive ceramic slips. Polyvinylidene fluoride (PVDF) is more resistant than polypropylene in plastic pumps.
The Air Side Materials (air valve, center section / non-wetted side of the pump)
The fluid you pump will come in contact with both the wet side and air side of the unit. This can lead to chemical spills and fumes in the pump. Therefore, the air-side must have the necessary chemical compatibility.
How Air-Operated Double-Diaphragm (AODD) Pumps Operate
The AODD pump operates in two cycles – suction and discharge. Let’s take a closer look at each.
The Suction Cycle
During the suction cycle, compressed air fills the left inner chamber. This causes the opposite diaphragm to create suction and lift the lower valve ball to pull in the liquid. Simultaneously, the left fluid chamber undergoes the discharge cycle.
The Discharge Cycle
During the discharge cycle, compressed air fills the right inner chamber. This causes the upper valve ball to open and discharge the liquid. Simultaneously, the left chamber undergoes the suction cycle.
Selecting an Air-Operated Double Diaphragm Pump (AODD Pump)
Although AODD pump solutions are easy to understand, it makes sense to know the specific components before selecting one. They can handle a wide range of chemicals, viscosities, and flow rates, and are applicable in many industries. Be sure to select pumps with maximum flow rates and minimum pulsation and air consumption.
Based on the guide above, please check if the pump meets your specific requirements.
Adler Tank Rentals offers air-operated diaphragm pumps from 2" to 3" for general fluid transfer. We offer 24/7 service, expert assistance, and transportation. The pumps meet stringent industry standards and undergo extensive testing.
Call us at 800.279.6310 or visit our website for a free quote.
How Long Do Diaphragm Pumps Last?
The motor in a diaphragm pump lasts for years. However, the diaphragm life ranges from just 6 to 12 months.
Can a Diaphragm Pump Run in Reverse?
No, diaphragm pumps cannot run in reverse because they rely on one-way valves.
Can Diaphragm Pumps Cavitate?
Cavitation is possible in the suction valve if it is not designed properly or the inlet pressure is not high enough during operation.
Is a Diaphragm Pump Submersible?
Yes, diaphragm pumps are fully sealed and submersible. You can also port the exhaust muffler to submerge the pump in any liquid.
AODD pumps have a simple and reliable technology with two air chambers and good suction lift characteristics. One of the main uses of this pump is that it can work with large solids without internal damage.