Screw Pumps: Quiet, Low Pulsation Pumps for Oils and Fuels

How a Screw Pump Works

Picture two or three screws meshing inside a close fitting housing. As they turn, the threads form sealed chambers that carry liquid along the length of the screws, from the inlet at one end to the outlet at the other. There are no valves and nothing moves back and forth, so the flow is smooth and continuous.

Because the screws turn steadily, these pumps offer a rare mix of strengths:

• Very low pulsation, so pipework, gauges and meters stay steady.
• Low noise, even at high pressure.
• High efficiency on thick fluids, because less fluid slips back as viscosity rises.
• Long life when the fluid is clean and lubricating.
• Self-priming, with good suction on most designs.

Types of Screw Pumps

Three Screw Pumps

One driven centre screw turns two idler screws, one on either side. The fluid itself drives and lubricates the idlers, so there are no timing gears. These pumps handle clean, lubricating fluids such as fuel oil, lube oil and hydraulic oil. Many reach pressures well above 100 bar while staying very quiet.

Two Screw Pumps

Timing gears keep the two screws apart, and the bearings sit outside the pumping chamber. Because the screws never touch, the pump can handle dirty, non lubricating or gassy fluids, as well as very thick products such as bitumen and heavy crude. These pumps can also run dry for short periods without damage.

Single Screw Pumps

A single screw turning in a rubber stator is better known as a progressive cavity pump. It suits sludge, solids and abrasive pastes rather than clean oils.

Screw Pumps in Hydraulic Systems

Three screw pumps also have a quiet career in hydraulics. Their smooth, pulse free flow makes them a favourite where noise matters, such as passenger lifts, injection moulding machines and test rigs. In a hydraulic power unit, a screw pump can cut noise and pressure ripple compared with many gear pumps. The trade off is a higher cost and a need for very clean oil, so good filtration is a must.

Getting the Installation Right

Screw pumps can run for decades when they are set up well:

1. Fit a suction strainer or filter. Three screw pumps rely on tight clearances and need clean fluid.
2. Keep the suction line short and large, especially for thick fluids.
3. Fit a pressure relief valve, or use the one built into the pump. A screw pump keeps building pressure against a closed valve.
4. Heat the pump and lines before starting on bitumen or heavy fuel oil. Cold product can stall the drive or damage the shaft.
5. Fill the pump with fluid before the first start, so the seal and screws do not run dry.

Screw Pump Specifications to Check

• Flow and pressure at your duty point
• Fluid type, viscosity range and temperature
• Two screw or three-screw design
• Shaft seal: mechanical seal or magnetic drive
• Speed and motor, plus any speed limit set by viscosity
• Inlet and outlet connections, and mounting
• Heating jacket or built in relief valve, if needed

Signs Your Screw Pump Needs Attention

• Falling flow or pressure, a sign of wear on the screws or housing.
• More noise than usual, which may point to cavitation from a blocked strainer or cold fluid.
• Leaks at the shaft seal.
• Higher motor current at the same duty.
• On two screw pumps, noise from the timing gears or bearings.

Most worn three screw pumps come back to full output with a new rotor set and seals, without replacing the whole pump.

Where Screw Pumps Work

• Fuel oil transfer and burner feed on ships and in boiler houses
• Lube oil systems for turbines, compressors and large gearboxes
• Hydraulic presses, lifts and machine tools
• Bitumen and heavy oil transfer and loading
• Crude oil and multiphase transfer in oil and gas
• Fuel unloading at depots and mine sites

Why Buy From TSA Hydraulics Engineering

As a screw pumps supplier, we check the viscosity, temperature and speed limits before we quote, not just the flow. You get clear prices in AUD, OEM or equivalent options, and help sourcing screw pumps replacement parts such as rotor sets, mechanical seals, bearings and timing gears. We tell you upfront whether a pump or part is genuine or an equivalent.