Progressive Cavity Pump Speed for Viscous Fluids – 2000 Series Engineering Guide
Viscosity can limit progressive cavity pump speed because the pumped fluid must have enough time to enter and fill the progressing cavities.
This engineering reference explains how viscosity affects recommended operating speed and element selection for Moyno® 2000 Series pump configurations.
Why Viscosity Changes Progressive Cavity Pump Speed
As viscosity increases, a progressive cavity pump may need to operate at a lower speed to allow the fluid to flow into and fill the pumping cavities. If the pump runs too fast for the fluid to fill the cavities completely, volumetric efficiency can decrease. The practical response is often to reduce RPM and, when required flow must be maintained, select a larger pumping element.
Viscosity alone does not fully describe every fluid. Non-Newtonian materials can change apparent viscosity with shear rate or time, so actual application behavior should be considered when sizing the pump.
2000 Series Suggested Maximum Pump Speeds for Viscous Fluids
The 2000 Series viscosity-selection table evaluates pumping elements at 1,000, 2,500, 5,000, 10,000, 30,000, 50,000 and 75,000 cP. The table is intended as a selection limit: as viscosity increases, the recommended maximum RPM generally falls, and a larger element may be required to maintain capacity.
Important Selection Note
Beyond the maximum viscosity listed for an element, volumetric efficiency can be less than 100% even at the maximum recommended RPM. Final speed and capacity should therefore be checked against the applicable performance curve and the actual fluid behavior.
Viscosity Range Used for 2000 Series Selection
| Viscosity | Selection Consideration |
|---|---|
| 1,000 cP | Beginning of the published high-viscosity speed-selection table. |
| 2,500 cP | Worked polymer example demonstrates speed correction for incomplete cavity filling. |
| 5,000 cP | Maximum recommended RPM is reduced for many elements. |
| 10,000 cP | Lower-speed operation becomes increasingly important. |
| 30,000 cP | Larger element selection may be required to maintain flow at reduced RPM. |
| 50,000 cP | High-viscosity duty requires careful inlet and performance review. |
| 75,000 cP | Upper viscosity column in the published 2000 Series selection table; not every element is suitable to this viscosity. |
Worked Example: 2,500 cP Polymer
A polymer-feed example requires 16 GPM at 2,500 cP. From the water performance curve, a No. 6 element would require approximately 330 RPM to produce 16 GPM. Because the polymer does not fill the cavities like water, the operating speed must be corrected for viscosity.
The viscosity table shows the No. 6 element can operate at up to approximately 430 RPM at 2,500 cP. Using the viscosity-corrected performance procedure, the required speed remains within that limit, so the No. 6 element is acceptable for the example.
Engineering Lesson
Do not select a progressive cavity pump for a viscous fluid from a water curve alone. First establish the water-curve speed required for the desired flow, then account for viscosity and verify that the corrected operating point remains within the recommended speed range for the selected element.
Fluid Rheology Matters
| Fluid Class | Behavior |
|---|---|
| Newtonian | Viscosity remains constant regardless of shear rate. |
| Non-Newtonian | Viscosity changes in response to shear rate and possibly time. |
| Pseudoplastic | Viscosity decreases as shear rate increases. |
| Dilatant | Viscosity increases as shear rate increases. |
| Bingham Plastic | Flow begins after an initial yield stress is exceeded; apparent viscosity then decreases with increasing shear. |
| Thixotropic | Viscosity decreases with shear rate and with time under shear. |
| Rheopectic | Viscosity increases with shear rate and with time under shear. |
Viscosity and Abrasion Must Be Checked Together
A fluid can be both viscous and abrasive. In that situation, the allowable operating speed should satisfy both limits. Use the more restrictive speed and then select an element large enough to provide the required flow at that RPM.
See the 2000 Series Abrasive Fluid Speed Guide →
Need Help Selecting a Pump for a Viscous Fluid?
Send ACCA the required flow, viscosity, fluid description, temperature, suction conditions, differential pressure, solids information and available pump model. We can review the element size, operating speed, materials and stage configuration for the application.
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