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Positive Displacement Pumps vs. Centrifugal Pumps

Hi Brother John, Forget the details and concentrate on the principles. A positive displacement refers to the fact that a bellows has a certain volume, OK? When it opens, that creates a vacuum representative of the volume it just displaced. The faster it opens determines the negative pressure (vacuum pressure) in inches of water. In all vacuum pumps of both kinds, the pressure will be inversely proportional to the cu. in/minute, but positive displacement can generate much higher pressures exponentially as air volume decreases linearly. However it is greatly limited in its cu in/min air volume capacity. The centrifugal pump's cu in/min air volume increases somewhat exponentially with a larger and larger area opening. A centrifugal pump is no more than a fan blowing away from you. So you box it in a tube and give it an exhaust, and the vacuum pressure it creates is proportional to its size, velocity, and inversely proportional to its cu. in/minute draft. Its pressure decreases linearly as its air volume decreases exponentially (sort-of). In other words, it's an air-volume-sort-of, vacuum pump. The positive displacement pump can never pump the equivalent volume of air but it can reach higher pressures faster. The centrifugal pump is called "centrifugal" because it grabs the entrained air in the 'tube' system from its center and throws it away at its outside edges. That's centrifugal force. A centrifugal pump will work as a replacement for an Ampico pump because Ampico pumps are designed around a spill valve. The centrifugal pump itself is also a type of spill valve, whose very principle is designed around air "slippage." Only a positive displacement pump will work for a Duo Art and the only "safety valve" (or limiting pressure factor) in a Duo Art is a slipping belt or a stalling pump motor. Even the "Soft" setting in a D/A relies on a positive throttle on the modulator which just changes the size of hole the expression box is allowed to operate from. Brother Craig On 9/21/2018 2:17 PM, John A Tuttle wrote: > Hi Brother Craig, > > I'm trying to see if I understand the main difference/s between positive > displacement and centrifugal when it comes to generating a vacuum.

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