- 1 Screw Pump Working Principle
- 2 Types of Screw Pumps
- 3 Components of Screw Pump
- 4 Advantages and Disadvantages of Screw Pumps
- 5 Applications of Screw Pumps
- 6 FAQ Section
A screw pump is a famous type of the positive displacement pump. It is also called a water screw pump. A screw pump uses one or more screws to move fluids or water along the axis of the screw. These screws interlock to pressurize the fluid and move it inside the system. These screws are meshed with each other and reciprocate in the cavity of the cylinder.
In this pump, the water or other fluids enters into the pump through the inlet valve and flows linearly toward the outlet side of the pump along with the interlocking screws. The small gap between the screw and the cavity increases the fluid pressure when fluid flows through the pump.
Rotary screw pumps are used in various industries such as power generation, shipping, chemical processing, terminals, refineries, pipelines, and oil and gas production. In the power generation zone, these pumps use for jacking oil, fuel supply, high-pressure fuel injection, gear and bearing lubrication, and water power for applications in the control of hydroelectric plants.
The water screw or screw pump is a machine that needs very low maintenance and has few rotating components. With the help of these pumps, you can effectively pump fixed volume products in a variety of viscosity, pressure, and volume ranges.
A screw pump has an easy and reliable construction. It is very easy to design. There are three screw spindles, two of which are driven screws and the other one screw is a driver. There is enough clearance between these screws, which is responsible for pumping the water or other fluid. The electric motor supplies the fluid to the screws.
This type of pump has a housing with suction and discharge sides. The suction valve is located at the pump base, while the discharge valve is located at the top of the pump. In addition, it has a check valve at the discharge side that prevents the backward flow of the fluid. All of this can observe in the pump design.
Read also: Different types of Pumps
Screw Pump Working Principle
The screw pump is a positive displacement pump. This indicates that the liquid is moved by consistently displacing the space occupied by the liquid. The screw pump drives by two counter-rotating screws, which design in such a way that they rotate toward each other.
As the screw pump starts operating, the power is supplied to the driver screw through an electric motor. A driving shaft is connected with the driver screw that drives the driver screw.
As the driver screw starts rotating, the driven screw also rotates with its rotation because these screws meshed with each other. Due to the movement of these screws, a minimal vacuum starts producing at the inlet section. Due to this vacuum, the fluid sucks inside the pump from the inlet valve.
As the fluid enters into the pump, it traps in between the gap of the “screws.” This trapped fluid also moves with the rotation of the screws. Due to the movement of the screws, the volume of the trapped fluid reduces, and the pressure of the fluid increase.
When the pressure of the fluid increases according to the desired pressure then it discharges from the outlet valve and transfer to the desired location.
When screw pumps are pumping oils or other types of viscous liquids, the screw’s surface is lubricated when the liquid pumps so that there remains little or no gap between the screws.
However, when pumping gas/water mixtures, water, or other types of light liquids, these components can’t come into contact with one another. Without contact, the parts wear out quickly. Therefore, do not use a three-screw pump (where one screw drives the other two without a gear) for water supply or multi-phase operation.
For a better understanding, watch the following video:
Types of Screw Pumps
The screw pump has the following major types:
- Single Screw Pump
- Two Screw Pump
- Three Screw Pump
- Four Screw Pump
- Five Screw Pump
1) Single Screw Pump
Single screw pumps are also called PC pumps, worm Pumps, and progressive cavity pumps. In general, these pumps don’t consider in the category of screw pumps. This is a reversible pump. This screw pump works on the principle of positive displacement. It consists of a double spiral elastomer stator and a single spiral metal rotor.
These pumps are ideal for liquids that require a non-pulsating and steady flow. Single screw pumps are famous due to their excellent suction capacity. They use for many applications such as shipping, oil & gas, paint, sewage, papers, ceramics, chemicals, etc.
These pumps can effectively operate abrasive and non-abrasive fluids with or without solid elements (bilge water, sludge, sewage, etc.) and food (ketchup, yeast, gelatin, etc.). These pumps have very low costs. In addition, the single screw pump doesn’t clog.
2) Two Screw Pumps
It is also called a double screw pump. Because this pump contains two screws, therefore, it is known as a two-screw pump.
It is a most versatile pump type used in heavy-duty operations such as heavy oil pipe transfer. These pumps have self-priming and rotary abilities. The screws of this hydraulic pump drive with a motor and typically contain a gear for turning the next screw. These pumps use in food, energy, shipping, and petrochemical industries because of their brilliant performance.
The two screw pumps have the following properties:
- Can work at variable speed
- It can run dry
- Requires low NPSH
- Can handle a large volume of fluids and viscosities
- Tolerate contamination
- Low liquid sheer
- Excellent reliability
Read Also: Working of Centrifugal Pump
3) Three Screw Pump
This pump, also known as a triple-screw pump. It has three screws and an electric motor which drives the screws. It has one driver and two driven screws. The electric motor drives the driver screw, which further drives to driven screws. These screws mesh with each other.
These screw pumps use in small applications such as a lubrication system.
4) Four Screw Pumps
Basically, this is a two-screw pump, but each pump rotor has two screws that rotate in opposite directions.
This type of the hydraulic pump has four screws; due to that, it is called a four-screw pump. It sucks the fluid from the inlet port and distributes it evenly to both ends of the pump. The two liquids flow centrally with the help of a pump and again mix before leaving the outlet.
Like a two-screw pump, this pump includes a timing gear for operating the second rotor. Four screw pumps widely use in multi-phase and oil pipeline applications.
5) Five Screw Pump
The working of this pump is very similar to a three-screw pump. But it uses five screws instead of three. Also, like the three screw pump, this pump contains a submersible rotor to drive all screws. These pumps commonly use in many applications such as hydraulic and pipe oil.
See Also: Types of Reciprocating Pump
Components of Screw Pump
A screw pump has the following major components:
- Driver Screw
- Driven Screw
- Timing Gear
- Inlet & Outlet Ports
- Pressure Relief Valve
- Driving Shaft
1) Driver Screw
It is a rotating component of a screw pump. Driver screw connects with the driving shaft of the motor. It helps in pumping fluid at a constant volumetric flow rate. It’s one end connects with the timing gear, and the other end connects with the driving shaft.
The driver screw drives by the driving shaft of the motor, which further rotates the driven screw. It meshes with the driven screw. This screw is made of high tensile steel.
The primary function of the driver screw is to rotate the driven screw through an intermediate assembly called a timing gear.
2) Driven Screw
The driven screw is also made of high tensile steel metal. It rotates along its axis due to the movement transferred by the timing gear. It rotates in the opposite direction of the driver gear. This screw has a constant clearance area. This helps to catch water inside the tight clearance.
When the driver and driven screws move together, the water volume reduces and moves toward the outlet port. This movement increases the pressure of the fluid. After that, it discharges by the discharge/outlet port.
3) Timing Gear
The timing gear drives to driven screws in such a way that there is no metal-to-metal contact between the female and the male rotor assembly. It makes a connection between the driver screws and driven screws.
The timing gear gets rotation by the driver screw and transmits this rotation to driven screws. In this way, it drives to driven screws. It also ensures no such connections, even if the pump is idling for a short period.
Read Also: Working of Gear Pump
4) Inlet & Outlet Ports
A screw pump has different inlet and outlet ports. The inlet port uses to suck the water inside the pump, while the outlet port uses to discharge the water.
The inlet and outlet are designed so that there will be enough liquid medium when the pump finally stops. This supports delivering the initial liquid medium for the pump. Therefore, even if the suction tube is empty or dry, it should not dry out in a short time.
5) Pressure Relief Valve
As a subgroup of positive displacement pumps, screw pumps also build up the pressure even when the outlet is closed.
This builds-up pressure that can produce serious issues such as damage of pump internal parts and injury of the pump operator. Therefore, all positive displacement pumps have a relief valve to provide a sense of protection for the pump, the operator, and connected machinery. This valve sends back extra pressure to the inlet. Another famous way to neutralize additional pressure is to recirculate the outlet fluid.
In a vertically mounted screw pump, the upper bearings bear high loads as well as axial and radial forces during pump working. In this way, the stress on the lower bearings is very low.
The main objective of the lower bearing is to sustain the alignment of the pump parts. On the other hand, in parallel installed water screw pumps, roller, and sliding bearings have very low loads. This is because the produced radial and axial forces are opposite to each other and cancel out their impacts.
7) Driving Shaft
The driving shaft connects the drive motor with the assembly of the pump. This connection achieves by utilizing the appropriate set of flexible couplings.
In many types of pumps, this driving shaft works as a vital component of the pump and runs from side to side to secure the working of the driver screw. In such constructions, the drive shaft secures by a set of bearings that fit in the axial direction. Therefore, the proper alignment of the driving shaft is very important to ensure the pump’s service life and bearings.
Read Also: Types of Hydraulic Pumps
Advantages and Disadvantages of Screw Pumps
A screw pump has the following advantages and disadvantages:
Advantages of Screw Pump
- Screw pumps have many advantages over centrifugal pumps. First, the pumped liquid moves axially without turbulence. This eliminates bubbles created by viscous liquids.
- These pumps have easy maintenance.
- Screw Pumps can use for all fluids
- It can run dry ‘
- It has a compact construction
- These pumps deliver a constant and non-pulsating flow of fluid
- These have a quiet operation
- This pump can produce extended volumetric efficiency
- It needs very low maintenance
- High reliability
- Self-priming ability
- High robustness
- It has high tolerance against dust particles and water vapors
- It pumps the fluid with very high speed
- A screw pump doesn’t pump the contamination of the fluid.
- It has a frictionless rotation
- It has very high efficiency
- Low pulsations
- With screw pumps, you can also pump a high viscous liquid without losing the flow
Disadvantages of Screw Pump
- It is expensive to be installed for small industries.
- This pump needs a gas ballast to transfer light gas
- It has a very low pumping speed and worse ultimate pressure for light gasses without a gas ballast
Applications of Screw Pumps
- Numerous lubrication and hydraulic machines use screw pumps to supply oil to large machines.
- Screw pumps are more helpful to pump heavy oils. They even hold the ability to pump higher flow and higher viscous liquids.
- These pumps have the capability to pump liquid and gas simultaneously. Due to this reason, these pumps use in many pumping industries.
- This pump also uses for oil & gas, mining, and manufacturing industries.
- These pumps use in ceramics, chemicals, paint, food, and paper industries.
Screw Pump works on which Principle?
A screw pump works on the positive displacement principle.
Can screw pump run dry?
The answer is yes. A screw pump is designed in such a way that it can run dry without any damage or priming issues.
What is difference between screw pump and gear pump?
The main difference between gear pumps and screw pumps is that a screw pump generates low vibration, less noise, and less pulsating flow than a gear pump. The screw pumps also have long service life than gear pumps.