Screw Pump

P R E S E N T E D B Y:

PA D O N , M R I C K I M J I M J .
 • Definition of Screw Pump

• Parts of a Screw Pump

• Types of a Screw Pump

Overview • Advantages & Disadvantages

• Applications

• Specifications

• Maintenance
What is a
Screw
Pump?
• Screw Pump
 A screw pump is a type of rotary pump which is equipped with screws that mesh together and
rotate within a cylindrical cavity or liner. It is a positive displacement pump which can be built
with several screws. The fluid enters from the suction side of the pump and moves linearly
along these intermeshing screws to the discharge side of the pump. The clearances between the
screws and the liner are very small hence the fluid gains pressure while moving through the
pump.

 With better suction capabilities and low maintenance for the same range of speed; it is also
regarded as the most reliable pump for a variety of operation. A screw pump is known for its
low turbulence, ease of use with high viscous fluids, low vibration; self primed and ability to
work with minimal air pocket in fluid with low operating noise.
PARTS AND
FUNCTIONS OF A
SCREW PUMP
 The complete assembly consists of two main parts; the driving motor
( prime mover ) and the pump assembly. The motor provides the necessary
rotary motion to the pump drive screw coupled to its shaft; which
combined with low clearance in between screw create suction pressure.
1) Driver Screw - A driver screw is one of the rotating part of the screw pump; that helps pump the
fluid at constant volumetric flow at any point of rotation. With driving shaft connected on one side
and timing gear on another; it rotate with a close clearance with driven screw to push the fluid
axially forward along the angle of rotation. A driver screw is basically a screwed spindle made of
high tensile steel. The main role of driver screw in a screw pump is to drive the driven screw using
a intermediate connection called timing gear.

2) Driven Screw - Made of same material as of driver screw; a driven screw rotates along its axis in
effect of motion transmitted by timing gear. Unlike driver screw it rotates in the opposite direction
with a fixed clearance area. This helps to trap water or any other fluid medium within the close
clearance area. Now since both the screw spindles rotate in opposite direction without any change
in clearance area; it move the fluid axially along the rotating angle to give non pulsating output.

3) Timing Gear - The timing gear basically drives the driven gear in a way such; it does not lead to
metal to metal contact between male and female rotor assembly. One such contact can wear the
edge of the screw reducing the output pressure drastically. If remained unchecked it not only make
pump uneconomical and far less efficient; but also trigger the screws to lock to each other in some
cases. Thus a timing gear is installed on a screw pump to check such events.
4) Suction & Discharge Ports - A screw pump has different suction and discharge ports as the
fluid moves axially along the screw towards the discharge port. The suction and discharge ports
are designed as such; it holds enough fluid medium when the pumps finally stops. This helps to
provide initial fluid medium to the pump; avoiding it to run dry for a brief period of time even
with empty or dry suction pipe. The suction port is subjected to partial vacuum condition;
generated due to pressure difference between the suction port and the pump inlet.

5) Relief Valve / Recirculation Line - This can be achieved using a recirculating valve; that sends
back part of the fluid at outlet back to the suction port via an internal passage. In many modern
pump designs these relief valves came with an automatic flow control system; which maintains
the output pressure and flow at any given point of time. Thus to provide a sense of protection to
the pump, connected machinery and operating person; all positives displacement pumps
including this are equipped with relief valve. The other common method used to neutralize
excess pressure is via outlet fluid re-circulation.
6) Bearings - In vertically mounted screw pumps the upper bearing is subjected to high load; along
with radial and axial forces during pump operation. On other hand the lower bearings are
subjected to very low load; with an important task to maintain the alignment of the pump
components. In horizontally mounted screw pump both the sliding and roller bearings; are
subjected to almost no ( Low ) load and forces due to pump action. It is so because the axial and
radial forces generated oppose each other to nullify their effects.

7) 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 pumps dry side and the working liquid. This
keeps the bearings and the timing gear separate on one side of the pump.

8) Driving Shaft - It is the part of the pump that connects the pump assembly to its driving motor.
This is achieved by using a proper set of flexible couplings.
Types of a
Screw
Pump
“Screw pumps are available in a variety of different
designs.
Single Screw Pump / Archimedean
• One screw pumps are referred to as Progressive Cavity Pumps, sometimes called PC Pumps or
Worm Pumps. These are generally not considered in the Screw Pump family because the rotor
used in these pumps is not shaped like a typical screw, but rather a twisted round shaft. A
Progressive Cavity Pump has one shaft that is slightly twisted in the shape of a screw, and is
housed in a pumping chamber that is usually rubber lined.
Double Screw Pump
• The two screw pump, also known as the twin screw pump, is the most common type for high
power applications such as heavy oil pipeline transfer. One of the screws is driven from the power
source (motor, engine, etc.), and timing gears are usually incorporated to rotate the second screw.
Three Screw Pump
• The three screw pump, also known as the triple screw pumps, is typically used for small
applications, such as lubrication systems. One of the screws is driven from the power source,
which then rotates the other two screws around it, without the use of timing gears.
Four Screw Pump
• The four screw pump is essentially a Two Screw Pump, but with two screws per rotor, each facing opposite
directions. The four screw pump sucks fluid in the suction port, then splits equally and is routed to both
ends of the pump. The two fluid streams flow through the pump towards the middle and join together again
before exiting the discharge port. Like the twin screw pump, the four screw pump has timing gears to drive
the second rotor. Four screw pumps are often used in Multi-phase applications as well as oil transfer
pipelines.
Five Screw Pump
• The five screw pump is primarily the same as a triple screw pump, but with 5 screws instead of 3.
Like the three screw pump, the five screw pump has 1 diving rotor that drives all of the other
screws. The five screw pump is often used in lube oil or hydraulic applications.
 • Wide range of flows and pressures
• Wide range of liquids and viscosities
• Built-in variable capacity
• High speed capability for freedom of driver
selection
• Low internal velocities
• Self-priming with good suction

Advantages •
characteristics
High tolerance for entrained air and other
gases
• Minimum churning or foaming
• Low mechanical vibration, pulsation-free
flow, and quiet operation
• Rugged, compact design - easy to install
and maintain
• High tolerance to contamination in
comparison with other rotary pumps
• Relatively high cost because of close tolerances and
running clearances
• Performance characteristics sensitive to viscosity
change
• High pressure capability requires long pumping
elements 
Disadvantages
Due to their ability to provide high flow rates
even in viscous liquids, screw pumps are
ideal for:

• Fuel Transfer
•
•
Sewage Inlet Pumps
Storm Water Pumping
Applications
• Drainage Pumping
• Hydraulic and Lubrication System
• Heavy Oil Pipeline
• Multi-Phase Pumping
SPECIFICATION
The screw pump application ranges:
• Flow Rate Ranges – 50 to 15,000
gallons per minute, 189 to 56,781 liters
per minute
• Total Head (Pressure) Ranges – 50 to
4,500 psi, 3 to 310 bar
• Horse Power Ranges – 5 to 5,000
Maintenance

• Even with the ability to withstand extreme running conditions; it do need maintenance and good
housekeeping for prolonged operational life. A screw pump must never be run dry deliberately; as
any dry run more than a minute or two can damage the pump parts. Care must be taken to avoid
extreme pressure buildup due to output valve shut.

• Proper checks and maintenance must be done at regular interval of time; with time between two
maintenance schedule not exceeding three years. Suction and delivery pressure must be monitored
regularly with a quarterly need to clean pump strainers. A dirty or chocked suction strainer will
lead to reduced suction pressure.
 References
• https://www.powerzone.com/resources/glossary/screwpump
• https://shipfever.com/screw-pump-parts-working-function/
• http://maritime-engineering.blogspot.com/2018/06/the-advantages-and-disadvantages-of.html
• https://empoweringpumps.com/screw-pump-basics/