What Is a High Viscosity Pump?

Defining Viscosity and the High Viscosity Pump

Viscosity is a liquid's internal resistance to flow, usually expressed in centistokes (cSt). Water sits near 1 cSt at room temperature; heavy fuel oils reach thousands of cSt and food pastes, resins and bitumen can reach hundreds of thousands. The higher the viscosity, the more the pump technology itself decides whether the duty succeeds.

A high viscosity pump is not a single machine type but a class of positive displacement machines selected for such fluids — our industrial pump types overview groups every major technology by operating principle and duty.

Why Positive Displacement Is the Defining Principle

Centrifugal pumps convert impeller velocity into pressure and flow. In a thick liquid, friction in the impeller and casing makes head and flow fall while efficiency drops steeply. Positive displacement (PD) pumps work the other way: each revolution traps a fixed volume, so flow is set mainly by speed and a thicker liquid improves internal sealing. The two families are compared in depth in our positive displacement vs centrifugal pump article.

External gear pumps move clean oils compactly, while rotary lobe pumps handle shear-sensitive and hygienic products gently — the trade-offs are laid out in our rotary lobe vs gear pump comparison.

Screw Pumps: The Viscosity All-Rounders

The most common high viscosity pump is the screw pump, and the name covers two machines. The G-type single screw is a progressive cavity pump: a helical metal rotor turns inside an elastomeric stator, forming sealed cavities that travel from suction to discharge with low-shear, near-pulseless flow. Qingdao Green Power publishes it for high-viscosity oils and resins above about 1500 cSt, sludge, slurry, bitumen, food pastes and shear-sensitive polymers, at 0.1–150 m³/h and 0.6–2.4 MPa. The stator elastomer (NBR, EPDM or FKM) must match the chemistry and temperature of the liquid, and the pump must never run dry because the rubber stator is destroyed within seconds.

The 3GB triple screw pump is the other family: three intermeshing screws convey clean, low-viscosity oil axially with balanced loads, giving quiet, low-pulsation flow up to 350°C at 2.4–241.7 m³/h. Both families are presented on the G and 3GB industrial screw pump product page.

Where Centrifugal Pumps Fit — and Where They Stop

Centrifugal pumps remain the right tool for water, solvents and thin process liquids, where continuous, non-pulsating flow and low cost dominate. Qingdao Green Power's IS/ISW centrifugal pump range is published at 1.5–1600 m³/h with heads to 125 m, but the guidance is clear: above about 150 cSt, switch to a gear or screw pump, and thick, shear-sensitive media point further toward progressive cavity or lobe designs.

Choosing a High Viscosity Pump: Practical Checks

Selection starts with the fluid, not the catalogue — the same discipline as in our industrial pump selection and viscous fluid pump selection guides:

• Viscosity and temperature at the worst case: size for the coldest, thickest condition — it drives torque and suction.
• Flow and discharge pressure: PD flow rises with speed and is largely independent of pressure; confirm the maximum pressure and fit relief protection.
• Solids and shear sensitivity: abrasive or fragile products point to progressive cavity or lobe designs, with solids kept below the minimum flow passage.
• Elastomer, seal and material: match stator rubber, seal type and wetted materials to the chemistry and temperature of the liquid.
• Dry-run protection: progressive cavity pumps in particular must never run dry — fit low-level protection.

Frequently Asked Questions