The design principles of screw pumps are similar to those of positive displacement pumps, which pull fluid out to the discharge side by creating a vacuum inside the pump. They combine their resilience and adaptability for a wide range of applications and industries with the characteristics and advantages of lobe, centrifugal, and piston pumps.
In this article, we will explore what a screw pump is, it’s application, diagram, types, and how it works. We also discussed its advantages and disadvantages
Let’s begin!
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What is a screw pump?
One or more screws are used in a screw pump, sometimes referred to as a water screw, which is a positive displacement (PD) pump that transfers liquids or solids along the screw axis. In its most basic configuration, a single screw moves the material along its spindle while rotating in a cylindrical hollow.
Many low-tech applications, including agricultural equipment used to move grain and other solids and irrigation systems, still make use of this antiquated design.
The development of the screw pump has given rise to other multi-axis technologies, wherein precisely designed screws either stay motionless in a chamber or revolve in opposing directions. The substance being transported can be “locked-in” to the cavity by profiling it.
A three-spindle screw pump is frequently used in offshore and marine systems to pump viscous fluid at high pressure. In a closed chamber, the pumped liquid is propelled by three screws. Along the screw’s spindles, the pumped liquid travels while the screws revolve in opposing directions.
Screw pumps with three spindles are used to move lubricating, viscous liquids. They can be used for a number of purposes, including hydraulics, fuel, lubrication, circulation, supply, oil burner, supercharging, and fuel injection.
Comparing positive displacement pumps to centrifugal pumps reveals a number of benefits. In contrast to viscous liquids, which would otherwise froth, the pumped fluid travels axially without turbulence.
Liquids with a higher viscosity can also be pumped without reducing flow rate. PD pumps are also barely affected by changes in the pressure differential when compared to centrifugal pumps.
Applications of a Screw Pump
Screw pumps are becoming the preferred option for many companies because of their numerous uses and versatility across a wide range of sectors.
These are perfect for viscous and shear-sensitive materials since they guarantee that the product you’re pumping won’t get harmed while the pump is operating.
In addition, they are effective for the following uses, albeit these are not the only ones: filling, suction feeding, Supply supply, flush dosing, loading and unloading SIP and CIP
Sturdy fluids with lubricating qualities are transported by three-spindle screw pumps. They may be used in many different applications, including lubrication, circulation, feed, hydraulics, boosting, oil burners, fuel injection, and so forth.
Among the uses for screw pumps are the following. Oil, manufacturing, gas, and mining are just a few of the sectors that use these pumps extensively.
The majority of pump applications include high-viscosity fluids, such as asphalt;
In other cases, they involve oil or multi-stage liquid, which implies that fluid and steam are combined together in the liquid stream. These pumps are utilized in a variety of systems, such as heavy oil pipelines, hydraulic systems, lubrication, and multi-phase pumping.
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Diagram
Types of a Screw Pump
There are several screw pump varieties with a variety of designs on the market. Below is a quick discussion of them.
1. A single-screw pump
These pumps are also known as worm pumps and progressive cavity pumps, or PC pumps. These kinds of pumps are typically not regarded as belonging to the screw pump family. Because the rotor of these pumps resembles a twisted round shaft rather than a typical screw.
A progressive cavity pump is housed in a pumping hall that is often coated with rubber and has a single shaft that is slightly twisted like a screw.
2. Two-Screw Pump
These pumps, also known as double screw pumps, are the most often used kind for high power applications, such as the transfer of heavy oil tubes. The motor powers the screws in the pumps, and timing gears are typically provided to turn the next screw.
3. Three-Screw Pump
Often employed in minor applications such as lubrication systems, these pumps are also known as triple screw pumps. Without the need of timing gears, the motor in the pump determines how to rotate the other two screws around it.
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4. A pump with four screws
These are essentially two-screw pumps, except each rotor has two screws pointing in opposing directions. The liquid is absorbed by these pumps in the suction port, then divided equally and sent to the ends of both pumps.
With the pump’s assistance, the two liquids move towards the centre and re-connect before exiting the release port. This pump has a timing mechanism to turn on the second rotor, just like the double screw pump. These pumps are commonly used in oil transport pipes and multi-phase applications.
5. Pump with Five Screws
These pumps resemble triple screw pumps in most ways, however they have five screws instead of three. This pump has a single diving rotor that drives all of the other screws, just like the three-screw pump. This kind of pump is widely employed in a variety of hydraulic and tube oil applications.
How does a Screw Pump work?
Two perfectly crafted counter-rotating screw rotors that revolve “towards each other” power the screw pump. As a result, the gas is trapped between the rotor’s “screws.” This confined volume is decreased as the screws turn, compressing the gas and directing it in the direction of the exhaust outlet.
An electric motor provides power to the driving screw when the progressive cavity pump starts operating. The screwdriver that drives it is attached to the drive shaft.
Because these screws contact with one another, as the drive screw begins to revolve, so do the driven screws. A minimal vacuum begins to be created in the intake portion as a result of these screws’ movement. Fluid enters the pump through the input valve as a result of this vacuum.
The fluid is stuck between the “screws” when it enters the pump. As the screw rotates, this trapped fluid moves as well. When the screw rotates, the confined fluid’s volume shrinks and its pressure rises.
The fluid is released from the output valve and transported to the intended destination when its pressure rises in accordance with the target pressure. The lubrication of the screw surfaces during the pumping of oil or other viscous fluids results in little to no space between the screws.
However, these elements cannot come into contact with one another while pumping water, gas/water mixes, or other light liquids. Without touch, the components will deteriorate rapidly.
As a result, avoid using a triple screw pump for multi-phase operation or water supply, where one screw drives the other two without gears.
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Advantages of a Screw Pump
A sealed compartment is created within the pump case by the rotation of many screws that interact with one another in screw pumps. The fluid moves through the pump smoothly and continuously as the screwdrivers rotate.
In contrast to centrifugal pumps, which may be slowed down by viscosity or pumping pressure, it produces a volumetrically constant flow rate. The following are some benefits of screw pumps:
- Flexibility in dealing with various liquid kinds, viscosities, pressures, and flow rates
- Constant rates of flow
- Superior volumetric effectiveness
- Controllable results
- low internal speeds
- High resilience to air or gas entrained
- Quiet and seamless functioning
- Very little pulsation
- Features that self-prime
- Less vibration from the machinery
Disadvantages of a Screw Pump
When selecting the best pump system for your company, there are a few drawbacks to take into account, just like with any product design. Here are some examples for the screw pump:
- Can be expensive due to manufacturing with different rotating elements and high-quality materials.
- Not suitable for small pumping speeds below 100 rpm.
- Not suitable for highly viscous or abrasive fluids.
- High installation costs for small industries.
- Requires gas ballast for light gas transfer quality.
- Cannot scale down to small pumping speeds below 50 m³/h; multi-stage roots or scroll pumps used.
- Bulky and heavy.
- Sensitive to fluid viscosity changes.
- Low volumetric and mechanical efficiencies.
- High manufacturing cost of precision screws.
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FAQs
What is the purpose of a screw pump?
When pumping heavy oil, screw pumps are more useful. They can even pump fluids with greater viscosities and flow rates. Both liquids and gases can be pumped using these pumps. Because of this, a lot of pumping businesses employ these pumps.
What is another name for a screw pump?
One Screw Pump – One screw pumps are referred to as Progressive Cavity Pumps, sometimes called PC Pumps or Worm Pumps.
Where is a screw pump used in a ship?
This single screw marine pump is frequently used as a sludge or bilge pump. It is utilised, for instance, in waste water treatment units and oily water separators. Single screw pumps are frequently used on ships and other vessels for the discharge of bilge, sewage, sludge, oily seawater, and other materials.
Where are screw pumps used?
Oil-free screw pumps are frequently used in food processing, drying, packing, and even freeze dryers to prevent water or process debris from contaminating the pump oil. Screw pumps are used as roughing pumps for high vacuum pumps in large-scale coating applications, such as architectural glass coaters.
What are the different types of screw pumps?
Pumps can be categorised according to how they move, including gravity pumps, steam pumps, impulse pumps, velocity pumps, electromagnetic pumps, positive-displacement pumps, and valveless pumps. Axial flow, centrifugal, and positive displacement pumps are the three main categories of pumps.