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Dynamic or kinematic viscosity with gear pumps

Dynamic or kinematic viscosity with gear pumps

Dynamic or kinematic viscosity with gear pumps

Most specifications for gear pumps list a certain viscosity they are capable of handle at a given rpm, for example : 500 cSt @ 1440rpm. Is this referring to the dynamic viscosity of the moving fluid? I'm looking at charts for SAE crankcase oil viscosity and I see different ones for both kinematic and dynamic. My understanding is kinematic is the resistance to flow under the presence of gravity, dynamic is resistance to flow when an external force is applied. In my mind, I should be then looking at dynamic viscosity of the oil to determine if the pump can handle it correct?

Also, when a pump specification lists a max. viscosity at a certain rpm, what would happen if you were to try and pump a fluid with a higher viscosity? Would it potentially cause damage to the pump, or is the manufacturer simply stating that as a benchmark for how much flow the pump can deliver i.e., 10 gpm @ 500 cst and 1440 RPM, so anything higher than 500 cst would result in lower gpm?

RE: Dynamic or kinematic viscosity with gear pumps

centistokes (cSt) are a unit of kinematic viscosity, so if you know the density you can get dynamic (aka absolute) viscosity by the following relation:
kinematic * density = dynamic

If I had to guess, I would say you should use kinematic viscosity for Newtonian fluids because that represents the inherent resistance to flow of said liquid.
If you try to pump a higher viscosity liquid, both situations you listed can occur depending on where on the pump curve you end up; if my limited auto repair experience is to be trusted, the pressure will be more adversely affected than flow from your gear pump with the higher viscosity oil.

RE: Dynamic or kinematic viscosity with gear pumps

at high visc you will get a lot more internal shearing and heating.
The pressure goes down and you can damage both the fluid and the pump.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Dynamic or kinematic viscosity with gear pumps

"500 cSt @ 1440rpm. Is this referring to the dynamic viscosity of the moving fluid?"

The most basic way to answer this question is, cSt are a unit of what? There's your answer.

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