Key Parameters Often Overlooked When Selecting a Screw Pump: Viscosity, Temperature, Differential Pressure & Shear Sensitivity

 Key Parameters Often Overlooked When Selecting a Screw Pump: Viscosity, Temperature, Differential Pressure & Shear Sensitivity

Screw pumps are widely regarded as reliable, low-pulsation positive displacement pumps, making them a go-to choice for viscous fluids and demanding industrial services. However, many premature failures or performance problems occur not because of the pump itself, but because four critical selection parameters are overlooked during the design phase:

👉 viscosity, temperature, differential pressure, and allowable shear limits.

For more technical insights and real-world considerations, see:

🔗 https://www.scpv.cn/news/387.html

1. Viscosity: Not Just a Number on Paper

Viscosity is often treated as a secondary concern, yet it is one of the most important factors influencing screw pump performance.

A fluid’s viscosity directly affects:

Actual flow rate (high viscosity reduces effective pumping volume)

Required torque (higher viscosity demands higher torque from the drive)

Mechanical power (increased friction leads to more power consumption)

Selecting a pump purely based on “flow and head” without adjusting for actual fluid viscosity can lead to:

❌ Under-delivery

❌ Frequent overload alarms

❌ High energy consumption

❌ Premature wear of rotors and stators

Pro tip: Always use real, measured viscosity data at operating temperature rather than standard “water values.”

2. Temperature: A Hidden Multiplier of Effects

Temperature changes significantly impact screw pump performance in multiple ways:

Lowers or raises viscosity

Affects elastomer properties in stators

Changes fluid compressibility and density

Alters lubrication behavior of rotating parts

For example, a fluid with high viscosity at 20 °C may behave very differently at 60 °C. Thermal effects also influence material selection, seal compatibility and long-term component life.

Selecting a pump without considering temperature range is like building a house without checking the climate.

3. Differential Pressure: More than “Head”

In positive displacement pumps like helical rotor/screw pumps, the system differential pressure (ΔP) — the difference between suction pressure and discharge pressure — determines the actual load on the pump.

A high differential pressure means:

✔ Increased mechanical stress

✔ Higher torque demand

✔ Elevated energy consumption

✔ Elevated internal wear

If only discharge head is considered, ignoring the actual suction conditions and system backpressure, a pump may be under-specified and operate in an overloaded region.

Accurate ΔP calculation should integrate every real system resistance — piping, valves, filters, throttling, and downstream equipment.

4. Shear Sensitivity: A Factor Too Few Engineers Consider

One of the reasons screw pumps are popular is their low shear characteristics. But “low” isn’t “zero.”

For fluids that are shear-sensitive — such as:

Polymers

Emulsions

Biofluids

Gels and pastes

Food suspensions

even moderate shear can cause:

🚫 Molecular structure changes

🚫 Product degradation

🚫 Viscosity reduction

🚫 Emulsion breaking

For sensitive media, verifying fluid behavior under shear conditions is essential before specifying a pump.

5. The Real Trouble: Parameter Interactions

These four parameters don’t act independently. In real systems, they interact:

Temperature raises → viscosity drops → ΔP changes

High viscosity + differential pressure → torque demands spike

High shear sensitivity + variable flow → product quality issues

Without acknowledging these interactions, many selections succeed on paper but fail in practice.

Practical Selection Guidelines

To improve screw pump performance and reliability:

✨ Use real test data (viscosity at operating temperature)

✨ Calculate actual suction and discharge pressures

✨ Evaluate fluid sensitivity to mechanical shear

✨ Consult with manufacturers on materials and clearances

✨ Perform system simulations where possible

Selecting a screw pump is not simply picking a catalog entry — it’s matching fluid characteristics to mechanical capabilities.

Conclusion

While screw pumps have a solid reputation for handling viscous and difficult media, ignoring critical factors like viscosity, temperature, differential pressure, and shear sensitivity can undermine performance and shorten equipment life.

Good design starts by understanding the fluid — not just the numbers.

For deeper technical insights and case examples, check:

👉 https://www.scpv.cn/news/387.html