Pumps for viscous liquids Which pump type is most suitable for pumping highly viscous fluids in industrial service?

Introduction / Context:
Fluid viscosity strongly influences pump selection. Dynamic (centrifugal) pumps lose efficiency and capacity as viscosity rises, while positive displacement pumps maintain flow with less slip, making them preferable for viscous services like oils, syrups, and slurries.

Given Data / Assumptions:

• High viscosity fluids where Reynolds number is low.
• Steady flow requirements without excessive shear or heating.

Concept / Approach:
Screw and progressive-cavity pumps are positive displacement machines generating flow by trapping fluid in cavities and transporting it axially. Their performance is relatively insensitive to viscosity (within limits), unlike centrifugal pumps that rely on imparting kinetic energy and suffer large head losses at high viscosity.

Step-by-Step Solution:
Identify viscosity range: as viscosity increases, centrifugal efficiency drops and NPSH requirements rise.Positive displacement options (reciprocating, gear, screw) become favorable.Among them, screw/progressive-cavity pumps provide smooth, low-pulsation flow suitable for continuous processes.Therefore, the best general choice is a screw (or progressive cavity) pump.

Verification / Alternative check:
Manufacturer selection charts map acceptable viscosity ranges, consistently favoring PD pumps for high-viscosity applications.

Why Other Options Are Wrong:
Centrifugal and jet pumps are poor at high viscosity; air-lift depends on buoyancy with gas injection, not suitable for thick liquids; reciprocating pumps can handle viscosity but introduce pulsation and complex valving—screw pumps are generally preferred for steady viscous service.

Common Pitfalls:
Overlooking shear sensitivity of the product; ignoring suction limitations that demand careful NPSH margin for viscous feeds.

Final Answer:
Screw pump (progressive cavity/rotary screw)