Industrial Screw Pump for Viscous Fluids

Why Viscous Fluids Favour Positive Displacement

Centrifugal pumps lose performance as viscosity climbs: friction in the impeller raises losses, head and flow fall, and efficiency drops. Positive displacement pumps work the other way — higher viscosity improves internal sealing between the moving parts, so volumetric efficiency stays high. That is why pump selection based on fluid properties treats viscosity as a first-order decision; as a rule of thumb, above roughly 150 cSt a gear or screw pump replaces the centrifugal type, which is the published guidance for Qingdao Green Power's centrifugal range. The full logic is covered in our pump selection based on fluid properties guide and the high-viscosity pump selection article.

G-Type and 3GB: Two Screw Pump Families

"Screw pump" covers two very different machines. The G-type single screw is a progressive cavity pump — a helical metal rotor turning inside an elastomeric stator. The 3GB triple screw pump is a multi-screw rotary machine in which three intermeshing screws convey fluid axially. Choosing between them starts with the fluid: viscosity and temperature point to one family or the other.

Both are available through the industrial screw pump range. If the medium is thick, soft, solids-laden or shear-sensitive, the G-type is the candidate; if the duty is a clean low-viscosity oil at high temperature, the 3GB fits.

G Single Screw (Progressive Cavity): Viscous, Shear-Sensitive and Abrasive Media

In a progressive cavity pump the rotor-stator geometry forms a series of sealed cavities that move steadily from suction to discharge. Flow is smooth and nearly pulseless, and the large, gentle passages impose low shear on the product. The published application list for the G-type covers high-viscosity oils and resins above about 1500 cSt, sludge, slurry, bitumen, food pastes, biological fluids, shear-sensitive polymers and abrasive liquids — provided the solids stay below the minimum flow passage dimension. This combination makes it a standard answer for industrial sludge transfer and for products that a centrifugal or gear pump would damage.

Stator material is a selection input, not an afterthought

Because the stator is the wearing and sealing element, its elastomer must match both the chemical and the temperature of the medium. NBR, EPDM and FKM are the standard stator materials offered in this class of pump; each has a different resistance profile, so the grade is chosen against the actual liquid and operating temperature, not against the pump size alone.

3GB Triple Screw: Low-Viscosity Hot Oil

Where the G-type excels with thick media, the 3GB triple screw pump is engineered for the opposite corner of the viscosity map: clean, low-viscosity oil at high temperature. Its balanced three-screw geometry gives quiet, low-pulsation flow with good performance up to 350°C, which suits hot-oil circulation and heavy oil transfer systems where the oil is kept thin by heat. Because the pumped oil itself lubricates the screws, the 3GB depends on a clean, lubricating medium.

Running Rules That Protect the Pump

Screw pumps are forgiving of viscosity but unforgiving of abuse. Follow these operating rules to protect the machine and its elastomer:

• Never run a G-type pump dry. Without liquid, the elastomeric stator is destroyed within seconds — install low-level protection or a dry-run trip.
• Keep solids below the minimum flow passage. Oversized particles or hard agglomerates damage rotor and stator.
• Respect the pressure limit. Confirm the model's maximum discharge pressure and fit relief protection against a closed discharge valve.
• Check cold-start viscosity. A cold, highly viscous fluid raises starting torque — heat the line or confirm motor sizing for the worst case.

Not every viscous duty needs a screw pump: gear pumps handle many clean medium-viscosity oils more compactly. Our screw pump vs gear pump comparison helps draw that line before you specify.

Frequently Asked Questions