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Alternative Pumping Technologies- Air Operated Sanitary Pumps

November 25, 2013
Graco  Saniforce Sanitary Double Diaphragm Pump

Graco Saniforce Sanitary Double Diaphragm Pump

A lot of our recent focus has been on sanitary pumps and different pump technologies. All of these so far have been electrically driven pumps. An alternative to electric sanitary positive displacement or centrifugal sanitary pumps are air-operated pumps, namely air operated double diaphragm pumps and piston pumps. Holland is able to offer a full complement of sanitary air operated pumps and an overview of their application will be the focus of upcoming posts. This post will focus on sanitary air operated double diaphragm (AODD) pumps.

As stated in the introduction, there are two primary styles of air-operated pump: the air operated double diaphragm and the piston pump. The double diaphragm style pump is excellent for lower viscosity applications (<100,000 cps). Double diaphragm pumps utilize two pulsating diaphragm valves and ball or flapper style check valves. The working principle of an air operated double diaphragm pump (AAOD) is relatively straightforward. Compressed air flows into the right air chamber, causing the right diaphragm to flex. This expansion creates a high pressure in the right fluid housing equal to the air pressure applied to the pump.

As the inlet check valve of the right fluid housing closes, the outlet valve opens, and the fluid is pumped through the outlet manifold.  A rod connects the left and right pump chambers and as the pump shaft moves right it creates a vacuum in the left fluid housing.

The left inlet check valve then opens, the left outlet valve closes, and the fluid flows into the left fluid housing. The process repeats itself in the left chamber completing the cycle. The pump continues to cycle between the left and right chambers to effectively move fluid.

All AODD pumps have a 1:1 fluid to air ratio. This means the fluid pressure of the pump outputs will be approximately equal to air inlet pressure (somewhere between 50 and 120 psi depending on model). With high fluid delivery capacities (up to as much as 275 GPM), AODD are excellent choices for fluid transfer applications. Bulk tank loading and simple transfer are excellent applications for an AODD.

AODD are easy to install and their use of air makes them extremely convenient. They generate suction and self-prime. They are very portable, can be mounted on carts, and suction/discharge ports are reversible. AODD come in a wide variety of materials. Body materials include polypropylene and stainless steel. Ball and diaphragm materials include PTFE and santoprene.

AODD can handle a variety of products and are ideal for jams, jellies, fruit juice concentrates, and tomato pastes. While standard ball check style pumps are not suitable for stringy, particulate laden products, flapper style pumps allow particulates up to 2.5” in diameter to be handled. While flapper valves do not seat as effectively as ball check valves, they are ideal for meat poultry applications. Graco offers a dedicated flapper style pump specifically for these applications.

They are also very economical. They don’t require an AC induction motor. This allows them to be mounted in a variety of ways to reduce cost. Cost of an AODD is often 10% less than centrifugal pumps of comparable capacity.

Graco Sanitary Bin Unloading System using 2  Sanitary Double Diaphragm Pumps

Graco Sanitary Bin Unloading System using 2 Sanitary Double Diaphragm Pumps

Another big advantage of air-operated pumps is the lack of a rotating shaft seal. This allows them to be run dry. This allows them to be applied in sump type applications where we are trying to fully drain a tank. This also allows them to be mounted to a ram plate and used for drum and bin unloading. Sanitary drum and bin unloading products will be a topic of a future post.

Like any sanitary pump, AODD pumps do have limitations. They aren’t designed for high-pressure applications. As stated earlier, they have a 1:1 air to fluid ratio. If 100 psi air is supplied, 100 psi of fluid pressure will be output. Most AODD are limited to applications with pressure requirements below 120 psi. They also pulsate more than a lobe style pump, which can lead to excessive surge. Air also isn’t free. So while there are almost no electrical costs, continual air usage can be significant.

AODD are also loud. While pumps that use an AC induction motor often harmonically hum along, air pumps bang away. For reference, the maximum decibel level for a mid sized Graco 1040 AODD is 92 dBa at 100 psi or full flow. For reference, the University of Wisconsin Police used to inform me that my college dorm room parties were often in excess of 100 dBa and warranted a citation. While this level of noise isn’t conducive to studying, it isn’t usually an issue in an industrial setting; it’s just something to be aware of.

Holland is a certified distributor of the industry leading Graco sanitary air operated diaphragm pumps. While we do offer the industrial line (your Husky pumps), Graco’s primary sanitary offerings are the Saniforce series. Alternatives include Wilden pump and Murzan. The Saniforce product line will be the focus of future product focus posts. Contact Holland today with your product application and see if a pneumatic pump is a good fit for you.

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