What is Screw Pump | Definition, Construction, Working

Table of Contents

When a pair of meshing screws are used to increased pressure of oil, It is know as screw pump.

The screw pumps are available in design with one, two screws and three screws. This is two screw gear pump. It’s positive displacement pump.

It consists of following main parts

Screw pair – The meshing pair of screws is mounted with the help of spindle mounted in bearing. One of screw is connected to the driving shaft.
Timing gears – Timing gears are provided to maintain a running clearance between two meshing screws. With both the driver and driven screw running with a very fine clearance; there is always a chance of contact. One such contact can wear the edge of the screw reducing the output pressure drastically.
Suction and discharge port – A screw pump has different suction and discharge ports as the fluid moves axially along the screw toward the discharge port. Inlet suction port is provided for suction of oil and discharge port is provided to deliver high pressure of oil..
Housing – It is body of the pump which accommodates screw pair, timing gears and suction and discharge port.
Rotary and Stationary Seal – Screw pumps are fitted with a pair of mechanical seal with one on both side to act as a sealing surface between the pump dry side and the working liquid. This keeps the bearings and the timing gear separate on one side of the pump.

When pump is started by prime mover, the driving screw rotates and drives the other screw and creates suction of oil.
The oil entered through inlet suction ports is carried out linearly due to helical recesses between screw pair. The oil does not rotate but moves linearly .
Similar to gear pump, the meshing of the thread flanks forces oil to flow in the space between the rotor and housing wall.
The volume of the oil moves forward uniformly with the rotation of screw along the axis and oil pressure is gradually increased.
The oil from both the ends comes towards the centre of the pump where discharge port is located.
Now the oil is discharged through discharge port to the hydraulic system. The flow rate of the oil can be varied by varying the drive motor speed .

Screw pump can rech upto 180 to 56,781 liter per minute when it’s total head ranges 3 to 310 bar. Various sizes with pumping speed ~ 60 – 1200 m³/h are available.

It is used for fuel transfer, high pressure fuel injection, lubrication and hydraulic power implication.
It is suitable for industrial application like marine industry, refineries, chemical plant, heavy industries with hydraulic power control and power plant etc.

What are the types of screw pumps?
Screw Pumps Types
One-Screw Pump
Two Screw Pump
Three Screw Pump
Four Screw Pump
Five-Screw Pump
What is difference between gear pump and screw pump?
Gear pumps work by intermeshing gears with external or internal type. As gear pumps are virutally “single stage positive displacement” pumps with less pressure capability than screw pumps. Screw pumps have a longer screw where the pressure is divided along the length of the screw.