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Showing content with the highest reputation on 06/23/2019 in all areas

  1. 1 point
    I'd add AODD pumps to the mix. They seem to be the most popular pumps we sell for transferring liquids, particularly high-proof. Mash is another story unless you get a very large AODD. Centrifugal pumps are much cheaper in terms of dollars per GPM. Take something like our Dynahead 114, a centrifugal pump with a 1.5 HP motor and a maximum potential flow rate of 130 GPM. A similarly-specced flexible impeller pump in terms of size, motor HP, and price has a maximum flow rate of about 20 GPM. To get to 100 GPM with a flexible impeller pump you'll be spending at least twice the cost of the Dynahead 114 and have a motor about 3 times as powerful. That said, centrifugal pumps are not a total slam dunk. You have to work around them. They need to be primed, or to have liquid already running to their inlet in order to work properly. Manufacturers recommend against moving solids with centrifugal pumps, as the fast-spinning impellers will be damaged by abrasive solids (and at 3500 rpm, solids can be very abrasive). Additionally, if the inlet becomes clogged or the product you are trying to move is very viscous, you run the risk of cavitation. Cavitation is where there isn't enough material making it to the inlet of the pump fast enough. It causes vapor bubbles to form and it ultimately destroys the stainless steel impeller. The best way to be sure you're getting the right centrifugal pump is to understand the pumping conditions. Questions like: Will it have a flooded inlet? If not, how will you prime it? What is the tallest run you will have to pump? What kind of backpressure will it face as the result of any process valves, filters, 90° elbows, etc.? Will it have any pressure at the inlet? With those answers in mind, work with your centrifugal pump salesperson to spec the pump for a given duty point. That, or just overspec the hell out of it and buy more pump than you need to ensure your bases are covered and you are operating within the pump curve. Cavitation and viscous materials like mash are not such a big deal for flexible impeller pumps because they are a type of positive displacement pump, and the above-noted conditions don't make as much difference to positive displacement pumps. High temps are not good for flexible impeller pumps. At higher temperatures the impellers will swell. Since there's already a lot of friction in the pump head, the swelling increases the friction, and ultimately prematurely destroys the impeller. Sometimes very rapidly. Jabsco makes shortened impellers that are designed to swell to fit the head, however they're not as efficient at low temperatures, so you kind of have to choose one or the other: all high-temp or all low-temp (or swap impellers based on what you're pumping, but that'd be a pain). Centrifugal pumps are not great for high temperatures either, but for different reasons. A typical centrifugal pump uses a "Type D" that seals off the head from the shaft. At high temperatures the seal is more prone to fail or crack prematurely, and cause leaking behind the head. There are other seal styles that are better for high temp transfer, though. Some have a separate inlet to allow you to introduce water or other cooling agents to the head to keep the seal cool. Again, you'll want to work with your sales rep to go over which seal choice makes the most sense. There are a few "do-it-all" pumps we sell that can move hot, cold, thick, thin, near or far: Rotary Lobe, Piston Pumps, and Peristaltics. All are great, but none are cheap.


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