What is an Air Operated Double Diaphragm Pump and When Should You Use Them?

As we mentioned in our last post, today we’re kicking off a series of blogs to give you an overview of Graco’s line of Air & Electrically operated double diaphragm pumps and figured we’d start with AODD 101- what are they and when should we use them. So let’s take a closer look.

Let’s start with the basics- what’s an air operated double diaphragm pump or AODD and how does it work? Well, as the name implies, AODD’s use compressed air rather than an electrical motor to pump fluids.

Graco FG Series

Compressed air is supplied to the pump air inlet which drives an air valve. The air valve directs flow towards one of two diaphragms (connected by a rod) while simultaneously exhausting air from the opposite diaphragm chamber. This reciprocating diaphragm action pressurizes the discharge chamber and creates a vacuum on the suction chamber which actuates a series of product inlet and outlet check valves- drawing fluid in through a central inlet and pushing it through a central outlet. The check valves are typically ball checks, but flapper style valves are also available for products with large particulates.

AODD’s have no close fitting or rotating parts, which allows them to handle a variety of products with high solids contents. This also means no mechanical seal, so we can run and AODD pump dry without damage.

Graco HS/3A Approved AODD

This run dry capability coupled with the precision tolerances on Graco’s valve seats (manifold seats are actually lapped by a robot) allow the Graco AODD’s to create considerable suction lift and self-prime, even at dry start up and with heavier fluids.

Graco air operated double diaphragm pumps are easy to control by simply regulating the air inlet pressure. Depending on the precision required, this can be considerably less expensive than the variable frequency drives we use to regulate standard AC induction motors.

And because AODD’s use the air inlet pressure to “push” fluid through the pump, discharge line pressure can never exceed air inlet pressure, which means we can deadhead AODDs.

AODDs have a small footprint, especially for the amount of volume they can move, reversible inlet and outlet connections and can be quickly and easily installed- simply connect inlet and outlet connections and an air supply and you’re ready to go. As far as PD pumps go, they also deliver one of the best GPM/dollar ratios out there.

As mentioned previously, we love to use AODD’s with fluids that have large solids. The push/pull action, as well the minimal number of parts in contact with the product make AODDs exceptionally low shear.

The use of compressed air also means no electricity, so when properly grounded, AODDs are intrinsically safe. This makes AODDs excellent options in explosion proof environments.

Because there’s no rotors, gears, or pistons that wear over time, we not only minimize our maintenance cost, but also run with almost perfect efficiency until maintenance is required.

Saniforce 2.0 Drum Unloader

All of the above features- easy to control, run dry, self-prime, simple setup, ability to deadhead, high efficiency, and low shear- make them perfect for drum, bin and tote evacuation, coating applications, filter presses, general transfer, and counter pressure filler feed (more on that in a future post).

So what don’t we love about AODD pumps? There’s not too much, but there are a few things we should consider when specifying them. First, AODDs are generally louder than comparable electric pumps. They also tend to pulse, which is fine for transfer applications, but less desirable for precision dosing and metering applications. Supply air pressure can also be a limiting factor for higher pressure applications.

Graco EODD

Finally, because it takes a lot of electricity to make compressed air, it can be more expensive than the electricity needed to drive an electric pump. So if the pump is going to be running with high frequency, we may want to consider one of Graco’s electrically operated double diaphragm pumps for a lower total cost of ownership.

That’s AODDs in a nutshell. We love them for their ease of use, low shear handling, small footprint, and low up-front cost. AODDs are able to handle a wide range of flows and medium to high product viscosities. As always, if you have any questions about Graco’s Air Operated Double Diaphragm pumps, contact a Triplex Sales Engineer today!

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