Air-Operated Diaphragm Pump Qualities

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Air-operated diaphragm pumps are unique in that they are actuated with a compressed air and not a motor. The air pressure actuates diaphragms or bellows, and their reciprocating motion creates the pumping action. Due to this design, these pumps can pump a wide range of working fluids, from chemicals to food products of variable viscosity, and can run dry indefinitely. This quality comes down to the fact that there are no dynamic seals and that the flow rate is maximally adjustable (0% to 100%) based on air pressure. This allows for purity and durability for a wide variety of pumping situations. In Image 1, you can see the most common type of air-operated diaphragm pump (duplex) and its inner workings.

Image 1: Duplex air-operated diaphragm pump

For more information on air-operated pumps, refer to HI standard, Air-Operated Pumps for Nomenclature, Definitions, Application, and Operation (ANSI/HI 10.1-10.5) at www.pumps.org.

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Frequently Asked Questions (FAQs)

Q: How can I work out the air consumption for a pump?

A: Most manuals have performance charts which show air consumption figures based on a fluid delivery flow rate and air input pressure.

Q: Why would I need an ATEX approved pump?

A: If the area in which the pump is to be operated is designated as an ATEX zone, then you must use an ATEX certified pump.

Q: What is meant by &#;dry suction lift&#; and &#;wet suction lift&#;?

A: Dry suction lift refers to the pump needing to draw in the fluid from below the level of the pumps inlet. This means that the pump has to develop enough negative pressure (vacuum) to pull the fluid up the siphon tube and suction hose into the pump. Wet suction lift refer to the fluid level being above the inlet of the pump, in other words the pump inlet is flooded and therefore easier to prime than a dry lift installation and more able to cope with higher viscosity fluids.

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Q: The manual for my AODD pump states that the maximum pump speed is 400 cycles per minute. Is this the maximum continuous speed it can operate at?

A: No, maximum cycle rates are really just a benchmark figure based on pumping at free flow, so you can compare the performance of one manufacturers pump against another. It doesn&#;t represent a real world practical application. Typically a double diaphragm pump will be able to run continuously at between 40 and 60 cycles per minute and intermittently at much higher rates for short periods.

Q: The fluid I want to pump contains solid particles, can a double diaphragm pump be used?

A: Most double diaphragm pumps scan cope with solid particles, the maximum particle size will be stated in the technical specifications of each pump.

Q: How can I check if a pump is OK for use with specific fluids?

A: Contact our sales department who will be able to check chemical compatibility between your fluid and the wetted parts of the required pump.

Q: The exhaust outlet of my air powered pump keeps freezing up and this stops the pump from cycling, what can I do?

A: The air supplied to your pump contains a large amount of moisture which is freezing as it&#;s exhausted. As a minimum, fit an inline air separator upstream of the pump. If you have this already, check if it needs draining. The best thing you can do is invest in a refrigerant or desiccant dryer unit which all your air tools would benefit from.

Q: At a slow cycle speed my pump operates fine, but at faster cycle speeds the flow drops off and there&#;s pulsing out of the dispensing nozzle.

A: It&#;s likely that if the fluid you are pumping is quite viscous, at the faster cycle rates you are experiencing pump cavitation. This is when there is insufficient time for the pump to draw in the full volume of that stroke before the pump changes over to the next stroke. To prevent this, try using a larger and/or shorter suction hose if you are not able to reduce the fluids viscosity.

Q: I have a polypropylene DD pump, should this be connected to an earth i.e. grounded?

A: Polypropylene is not conductive so the pump cannot be earthed. However, the fluid delivery system should be grounded if you are pumping a conductive flammable fluid. Never use a polypropylene pump with non-conductive flammable fluids as any static electricity generate will not be able to safely dissipate to ground and could lead to an ignition spark.

Q: The image on your website of the Husky shows the outlet on the right, I need the outlet on the left, can I order a pump with the outlet that way round?

A: Husky pumps are supplied as standard with the inlet and outlet on the right but you can easily swap these around. There are instructions in each pumps manual on how to do this.

Q: The technical specs for the Husky 307 states that the air inlet is 1/4&#; NPT(F) is this the same as 1/4&#; BSPT?

A: No, although they look similar the threads are slightly different and not compatible. We can provide you with any size adaptors to convert between BSPT and NPT thread sizes whether for use on the air or fluid connections to a pump. Speak to our sales team for advice and pricing.

Q: Will a Husky 716 pump a fluid with a viscosity of centipoise?

A: Possibly, but we need to now more information about your application specifically; flow rate required, delivery pipework I.D. pipework length, head etc. so we can calculate the pressure drop. We&#;ll also need to check chemical compatibility so the advice is to speak to a member of our sales team before placing an order.

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