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FAQ: What Type of Pump Should be Used for a Running Viscous Liquid?

March 22, 2019

In fluid dynamics, viscosity is a function of flow resistance. That definition might make sense to an engineer, but it's not going to make much impact on a pump installer. Better to say, a viscous liquid has a thicker consistency. Low viscosity fluids, on the other hand, are those that are thin and watery. As for the pump types that suit the different fluid viscosities, please read on for more information.

What's The Best High Viscosity Pump Type?

Positive displacement suitability makes sure that all types of formidably high fluid densities are handled with equal efficiency. Prime examples of this pump type include progressive cavity devices and lobe pumps.

What's A Reciprocating Pump?

This is the second half of the positive displacement sector. In the first half, there are screw and lobe architectures, plus vane and gear mechanisms. A reciprocating mechanism operates by employing a backwards and forwards motion. Diaphragm and piston pumps occupy this group.

Where's The Low-Viscosity Equivalent?

Designed to draw Newtonian Fluid types, the oils and watery mixes, solvent bases and alcohols, centrifugal pumps deliver throttle-free power. They're commonly used in water systems and extra low-viscosity applications. Expect to see large centrifugal mechanisms employed as oil and fuel pumps, too.

Are There Different Viscosity Terms?

Yes, indeed there are different fluid types. Newtonian fluids already received a mention. Next, there are Pseudoplastic liquids, which are thick, but that thickness tends to decrease alongside an inversely proportionate rise in shear rate. Latex paints have Pseudoplastic properties. In this case, since centrifugal pumps cause shear, a progressive cavity pump would suit this application.

What's A State Changing Fluid?

In this context, a fluid becomes more viscous as it's pumped. As one example of this action, think about butter, which is a dilatant (agitation-sensitive) fluid. This milk-based product is soft and creamy, but as soon as it's pumped, it becomes thicker, to the point it will stall a conventional centrifugal pump. Thixotropic substances reverse this behaviour.

There were at least three takeaways that came to light as this FAQ progressed. Yes, low viscosity applications favour centrifugal pumps. Equally correct, positive displacement apparatus works exceptionally well as a high-viscosity solution. In between those two clear-cut pumping solutions, there are thixotropic and dilatant bases to process. To solve that last challenge, a pump engineer needs additional data. How thick is the fluid? Will it become more viscous or thinner when agitated? Shear problems are another issue, especially in viscous materials. Basically, as soon as a pump impeller lops off a thick fluid slice, its shear properties decide what happens next.

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