The workhorse for all applications
Throughout almost every area of industry, a role exists for the air-operated double diaphragm (AODD) pump. This is because its design allows the flow of the media being pumped to remain constant with the speed of the pump and furthermore, it is suitable for handling and transferring liquids of all types and consistencies even in the most challenging of environments.
To function, all that it needs is an electricity supply and the availability of compressed air.
Why AODD pumps?
The capabilities of the AODD pump are clearly demonstrated by its suitability to roles in many stages of production and processing, from the intake of ingredients from tanks through to transporting semi-processed and processed products around a manufacturing site right up to the place of distribution. Where it scores over many other types of pump is in its ability to pump shear-sensitive fluids, maintain the movement of both viscous and thick fluids and deliver leak-free operation. For many industries all this contributes to reducing product loss, lowering energy costs, optimising plant and equipment uptime, minimising environmental impact, whilst at the same time delivering products of the highest quality.
Working principle
For all its operating capabilities and advantages, the AODD pump is a relatively simple piece of equipment that has few moving components and is easy to maintain. The principle components are: an air distribution subsystem, air chamber, outer and inner diaphragm pistons, ball valves, valve seats, inlet and outlet manifolds, two fluid chambers and diaphragms.
An AODD pump contains two diaphragms that are connected by a shaft through the center section where the air valve is located. The diaphragms work as a separation wall between the air and the liquid. The purpose of the air valve is to direct the compressed air to the back of diaphragm number one causing it to move away from the center section. The number one diaphragm causes a press stroke moving liquid out of the pump. At the same time diaphragm number two is performing a suction stroke.
The air behind diaphragm number two is being pushed out to the atmosphere causing atmospheric pressure to push the liquid to the suction side. The suction ball valve is pushed away off its seat allowing the fluid to flow past the ball valve into the liquid chamber.
When the pressurised diaphragm number one has reached the end of its stroke, the movement of the air is switched from diaphragm number one to the back of diaphragm number two by the air valve. The compressed air pushes diaphragm number two away from the center block resulting in diaphragm number one being pulled toward the center block. In pump chamber number two the discharge ball valve is pushed off its seat, whilst in pump chamber number one the opposite occurs. Upon completion of the stroke the air valve leads the air again to the back of diaphragm number one and restarts the cycle.
Applications
AODD pumps provide an excellent method for handling for all kinds of liquids, whether thick pastes, solids-laden, aggressive or thin and with poor lubricity. Driven by a constant supply of compressed air, this pump type can be used in explosion proof areas where highly volatile liquids and gases are present.
Containing few components means that installation is simple and mean time before failure (MTBF) is extended, thereby contributing to lower maintenance. Furthermore, being seal-less, they are leak-proof; a factor which
makes them ideal for handling potentially hazardous fluids.
Verderair AODD pumps have a low component count. This means the pumps have fewer components to fail and are easier to disassemble and service. The components are of the highest quality with the diaphragms being moulded for strength and long servicelife.
The pump is sealed with an o-ring assembly, removing abrasive wear from the sealing system and with it, any risk of leakage via the seals.As all diaphragms in AODD pumps are a wearable part, it is recommended to inspect the condition of them as part of your regular maintenance procedure.
Left: A cut-away view of the Verderair Pure diaphragm pump. Visible is the diaphragm, air valve, seat assembly and of course, the flow path for the fluid to pass.
The Verderair Pure is purpose-built to handle the most aggressive fluids in the most hazardous environments in industry. Examples include concentrated acids, bases and even those with abrasive particles.
What makes it so suitable is the pump is built from 100% pure virgin PTFE or PE material so there is no metallic component in contact with the environment or fluids.
The entire unit is machined rather than cast to produce a pump with exceptional tolerances and fewer mechanical stress lines so the pumps efficiency is increased and the service life is longer.
To add to the reliability and service life, the diaphragms are over-moulded. Where the shaft is joined to the diaphragm there is a reinforced centre section. The diaphragm itself is designed to be more malleable and have an extended life.
A new generation of air valves comes as standard which use less compressed air and reduces the running cost.
In the case of Verderair AODD pumps non-stalling operation is guaranteed, even at low pressure and being self-priming they will run dry indefinitely without damage.
Pumping chemicals and abrasive fluids is always a challenge, but the AODD pump is particularly well suited to such applications especially those within the ceramics and surface coating industries. The pumps have excellent properties for handling paint mixture and adding pigments, whilst varnishes and laminates can be pumped without problems.
Verderair diaphragm pumps are used extensively for pumping chemicals such as acids, solvents, resins and latex, and for the most severe applications the solid machined non-metallic pumps are available. These diaphragm pumps are completely metal free and are made of solid machined pure PTFE and PE to ensure the highest levels of chemical resistance and leakage protection.
Where harsh environments are encountered and challenging fluids are being pumped, one major consideration has to be corrosion and the pumps must offer high levels of corrosion resistance. Consideration must also be given to the internal components with the materials for the wetted parts and elastomers being compatible with the nature of liquid being pumped and its temperature. Careful selection of the appropriate material for the diaphragms is essential and with the Verderair range there is no shortage of material options.
The external temperature in which the pump is working should not be overlooked. It is not unusual for pumps to be used in sub-zero conditions, the offshore oil and gas industry being one specific example, and external temperatures will influence the choice of materials from which the pump is constructed. As a rule of thumb, metals are best suited for extremely high and low temperatures and plastics for controlled environments.
configuration pumps in aluminium, with Teflon/Teflon diaphragms and stainless steel seats in 2-inch and 3-inch sizes have been supplied for pumping diatomaceous fluid to pre-coat and clean the filter press screen and removing excess water from the filter bed. The diatomaceous fluid is mildly aggressive, whereas the excess water being removed from the filter bed is much more aggressive slurry which could cause considerable damage and wear the internal components of the pump. The combination of the materials selected for the build of the pump, combined with its ability to be used where an electrical submersible centrifugal pump would struggle, has proved to be a successful solution for what is a highly challenging application.
The paint industry
The finishings and offshore industries provide a good insight into the workings, capabilities and flexibility of the AODD pump. The core ingredients for the production of paint are starch, oils, pigments, fillers and dilutions. All these present individual characteristics that can influence pump selection. For instance, with water based paints the pigments are less easy to dilute. In a paint production plant pumps are used to transfer the ingredients to preparation tanks to create a pre-mix. Following this pre-mixing stage the paint mixture is moved by another pump to the dispersion mill for a total homogeneous mixing. To complete the primary production of the paint, the homogeneous mixture is pumped to a dilution tank. Diluents are added, after which the paint is ready for further processing. All these tasks can be readily undertaken by an AODD pump, thereby giving the end user to opportunity to invest in a single pump type for the plant.
In the offshore production sector there is a demand for pumps that can operate in ATEX defined areas for handling aggressive chemicals, slurries and sludges. A sludge pump has to be resistant to abrasion as wear of the wetted parts will occur from the solid content in the fluid. The Verderair AODD pump can satisfy all these requirements. Filter press cleaning is an essential operation in well cleaning and provides a good example of the versatility of the AODD pump.
Left: The Verderair nonmetallic industrial range in ATEX conductive material. The standard industrial range is available in both metallic and non-metallic builds.
All of the Verderair range feature responsive air valve technology to maximise the amount of air used to move the fluid. More fluid is moved for the same amount of air used to reduce energy costs.
Verder UK supply pumps for virtually every chemical type and application. The Verder range includes leak-free mag drive pumps, chemically inert non-metallic AODD pumps, peristaltic dosing pumps for the accurate delivery of chemical including abrasive and solid-laden types.
Summary
The AODD pump is a versatile workhorse that enables users across a hugely diverse range of industries to standardise on a single pump type that for handling a wide variety of fluids. So long as there is a compressed air supply available the pump can be installed wherever it is required and should circumstances change it can be moved round a plant and switched to other operations with ease. Whether to fluid being handled requires a gentle pumping action, is chemically or physically aggressive the positive displacement AODD pump offers an efficient and low maintenance solution.
