The Guide to Air Diaphragm Pumps

Air Operated Double Diaphragm pumps, or AODD Pumps, are a fantastic solution for many facilities. They are extremely gentle and powerful. They can be inherently safer than standard electrical pumps, as they run on compressed air rather than electricity. This helps mitigate sparking hazards that could ignite flammable vapor. When you have the right air compressor, AODD pumps can push liquid up great heights and over long distances (you can find our guide on picking an air compressor here). But, as with all pumps, there are some considerations you should take into account first, and some basics you should understand before deciding on a pump. Let's get into it.

How do air diaphragm pumps work?

As usual, Wikipedia comes to the rescue with a nice illustration of the working principle of air diaphragm pumps in practice.

Air Diaphragm Pump Animation
The never-ending air diaphragm pump There'sNoTime, CC BY-SA 4.0, via Wikimedia Commons

Looking at the above illustration, it may be helpful to focus on just one side at first—either the left or right side. The black shape moving in and out represents the diaphragm. As it moves out, the ball on the bottom of the chamber moves down, creating a seal in the bottom of the chamber. At the same time, the ball at the top of the chamber moves out, which lets liquid pass out the top.

Then, as the diaphragm moves back in toward the center of the pump the bottom ball lifts up, while the top ball falls back down creating a seal against the top of the chamber. This lets liquid into the chamber from the bottom. That new liquid will in turn be pumped out in the next cycle.

Notice that as the diaphragm is extending on one side of the pump, another diaphragm is doing the opposite motion on the other side of the pump. So, there are two diaphragms operating oppositely from one another at the same time. One extending while the other retracts, and vice-versa. This is why they're called "double diaphragm" pumps.

Compressed air powers the motion of these diaphgrams, hence why their full technical name is Air-Operated Double Diaphragm Pumps, or AODD pumps, for short.

What are air diaphragm pumps good for?

Air diaphragm pumps are great for moving shear-sensitive liquids. There are no rotating surfaces inside the pump. Liquid is just pushed/pulled, so there is no shear except the normal shear that occurs as a result of moving fluid across any static surface

Assuming your air compressor can deliver high pressures, AODD pumps can also push liquids at high pressures. This means they are great for pumping thick or viscous fluids that need high pressure and slow pumping speed to move. They can also move liquid up great heights and over long distances.

They can be lightweight and compact, particularly ones that are made of polypropylene or other light polymers. They have no electric motor weighing them down, which is typically the heaviest part of electric pumps. That means small AODD pumps are used often for barrel work, where the user can just lift the pump around transferring to and from barrels.

Finally, because they don't use electricity they are often used in situations where the user is concerned about electrical sparks that could ignite flammable vapors. As a result, they are often the first choice for distilleries and ethanol extraction facilities, where there can be significant flammable vapors present, particularly in cases of spills or equipment rupturing.

What aren't air diaphragm pumps good for?

We've found that the easiest-to-use pumps are:

  • Self-priming
  • Dry-running
  • Reversible

AODD pumps are great at numbers one and two. They generate a good amount of vacuum at the inlet, which pulls liquid in and gets the pump started up. Air pumps can also run dry without any issues. Since they're not lubricated or cooled by any of the material they pump, you can run them dry without any issues.

AODD pumps are not reversible, though. They run in one direction only. While this is usually not a dealbreaker for most facilities, it's worth noting.

Air diaphragm pumps are not good for anything that has large solids in it. Smaller solids can be fine. We often get questions about whether or not you can use an air diaphragm pump for moving semi-solids. I.e., are they a good must pump or mash pump? The answer is, it depends. As with all pumps, you want to make sure your pump has a large enough inlet and outlet to be able to pass the largest solid in suspension. Air diaphragm pumps have a further barrier to pass solids through, though: the ball and check valve.

In the animation above you can see there are four balls that alternately block or pass liquid at various points in the pumping cycle. Any solid has to pass by that ball without blocking it or getting stuck. If something does get stuck we'll usually get a call from the customer, who says that the pump is "chugging, but not moving liquid". That's a sure sign that something is stuck in one of the check valves. To clear out the blockage the user must remove the top or bottom manifold of the pump to clean and dislodge whatever is causing it.

So, are they good must pumps? Nope. Wine must usually has many large, irregularly-shaped solids. It'd be very difficult to keep an air diaphragm from clogging on wine must. Anyway, there are definitely better choices when it comes to pumping must, so we advise against it.

Are air diaphragm pumps good mash pumps? They definitely can be, but they must be sized appropriately. If your mash has a uniform consistency with small solids, it's probably fine. Try and figure out the size of the largest solid you expect it to pass, and check against the pump's specs. It will usually note the largest solid in suspension it's capable of passing. Also, when you're done moving any solids, it's very important to rinse the pump thoroughly to prevent anything from sticking or gunking up the check valves. If you have any questions just ask us.

Maintenance & Troubleshooting of AODD pumps

All-in-all, air diaphragm pumps are more "plug & play" than just about any other type of pump. However, when things go wrong, they can be slightly harder to troubleshoot than electrical pumps until you become familiar with them.

Air pumps typically have two "sides": the "wet" side and the "dry" (sometimes called "air" side).

The wet side consists of anything that is in contact with the pumped liquid. This includes the diaphragm, the ball valves, and the valve seats. The dry side consists of anything that comes into contact with the compressed air, and transfers the power of the compressed air into the pumping action.

Fixing the wet side—say, a torn diaphragm or a clogged ball valve—is pretty straightforward. You just disassemble the pump partially, check the ball valve and seats for any knicks, scratches, or solids that would prevent it from sealing.

Fixing the dry side can be more daunting. There are just more parts to deal with. Thankfully VersaMatic produces videos that walk users through both wet and dry end rebuilds step-by-step.

A full rebuild usually consists of tearing down and rebuilding both the wet and the dry side. We sell wet and dry side rebuild kits for the pumps we carry. Replacing both the wet and dry side essentially makes it like a brand new pump.

Keeping Your AODD Pump Healthy with Dry Air

Air pumps generally require one thing above all to work well: clean, dry compressed air. If you are in a very dry climate then it's usually not a problem. If you are in a climate that is the least bit humid, however, you will want to get an air drier for your compressor. Any moisture in the air will travel through the compressed air lines and get into the dry side of the pump. It's called the dry side for a reason.

Moisture on a pump's dry side will cause components to fail prematurely, and inevitably leads to hard-to-pinpoint reliability issues that will eventually lead to full-on failures that aren't covered by warranty. When we're fixing pumps from humid climates it's easy to tell who's using an air drier and who didn't. The pumps with moisture in them are, well, nasty.

Refrigerated air driers are not too expensive. The upfront cost will pay for itself in saved pump downtime and rebuild kit costs, at any rate. We don't sell air driers, but companies that specialize in compressed air equipment certainly will.

Final Considerations

We separate our AODD pumps into categories according to what product they're best at pumping: SimpleWine for wine & beer applications, SimpleSpirits for distilled spirits producers that want a groundable pump, and SimpleSolvent for CBD extraction facilities that may be using the pumps at extremely low temperatures.

Beyond this, consider your target flow rate when selecting a pump. Bear in mind, we typically advise sizing one pump "up", if feasible. Air diaphragm pumps operate best and most smoothly when they are used at about 50-60% of their full capacity. Running them full out all the time tends to be hardest on the wear parts.

Air diaphragm pumps are famously noisy, and produce a rough, choppy flow that can be annoying. For that reason we build a pulse smoother that does a great job of smoothing out the flow of air diaphragm pumps.

We love air diaphragm pumps, and love talking pumps in general. Give us a call if you have any questions!

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