Screw Pumps

How do Screw pumps work?  

Twin, Triple and Multi-screw pumps operate on the same principle and are generally self-priming. All types are able to work with low and high suction pressure and a wide range of flow rates.  

Twin screw pumps use two spindles, one of which is a drive and one is a driven idler, or by external timing gears. Triple and Multi-screw pumps contain single power rotor that performs the pumping action, along with idler rotors which acting as rotating seals. All these designs are able to work with low and high suction pressure and a wide range of flow rates. The fluid flow is continuous, pulsation-free, not affected by turbulence and can be run at low and gentle flow rates to protect the product. Low internal fluid velocity and the gentle meshing o the rotors contribute to low shear rates, which is especially important for sheer-sensitive fluids.  They also have the ability to run at higher speeds for fast cleaning velocities/high volume delivery. Faster running speeds make it more economical when it comes to low viscosity media and volatile and gaseous fluids and, due to the smooth fluid path, the possibility of product separation is reduced.  

As a guide, flow rates typically range from 10mӠ/h to 5000mӠ/h, operating temperatures between 40°C and 150°C, accommodate pressures up to 150bar and are suitable for low and very high viscosity fluids ranging from 1cP to 1,000,000cP. 

Pump design 

The rotating geometry of the screws and the spaces between the intermeshing faces determine the pumping action and pulse-free flow. The angle and profile of the screw face has to be selected to handle the nature of the fluid being pumped. Screws are widely available in a range of different pitch configurations, giving them the flexibility to cope with the characteristics displayed by the numerous fluids and products encountered within a wide spectrum processing applications.   

The surface finish of the inner pump housing, pump screws and spindles is dependent on the nature of the fluid being handled. These do include hygienic finishes for foods, beverages, pharmaceuticals and aggressive and corrosive fluids. 

Advantages of screw pumps 

Screw pumps offer many advantages, notably in their design has better mechanical efficiency than other types of positive displacement pumps. This means that they use less power for the same capacity relative to a gear pump, thus saving energy costs. The essential factors that should be noted are: 

• Robust construction 
• Compact design 
• Self-priming 

• Work with low suction pressure 
• Dry running 
• Bidirectional flow 
• High efficiency due to internal compression 
• Constant pulsation-free product flow 

• low rotor wear 
• High and low pumping speeds  
• Suitable for use with variable speed drives 
• Suitable for CIP cleaning 
• Low life cycle costs 

• Handle shear sensitive and viscous fluids 
• Very low noise level 
• Handle gaseous liquids 
• No contamination of the medium. 

Applications  

The sheer versatility of the screw pump principle makes readily suited to handling fluids of all types and applications of both simplicity and great complexity. Untimed Twin Screw pumps have an established position in handling oils, emulsions, bitumen, chemicals and organic oils. Its simplicity of design makes it easy to service and operate where non-lubricating.   

Timed Twin Screw pumps provide very high running speed, large flow capacities and handle high discharge pressures. They too have a role in pumping challenging fluids, especially where low and high viscosities are involved. Faster running speeds make it more economical when it comes to handling less viscous liquids. However, the emergence of hygienic designs have now made them much sought after in food, beverage and sanitary products processing, where they are required to pump the product and also CIP fluids. The pulse-free flow is useful when feeding viscous products into homogenizers or temperature sensitive products into heat exchangers. Triple and Multi-Screw pumps are able to provide both very low and higher speed flows and are commonly associated with handling heavy duty oils and fuels where viscosities are high and operating speeds low. Running at higher speeds provides increased efficiency. Equally, they are used extensively handling the very low viscosities associated with products such as aviation fuels, biodiesel and low sulphur diesel. Major applications where they are used include marine engineering, power generation, hydraulic systems and lubrication systems involving high viscosity gear lubricants and fuel oils.  

Considerations when selecting screw pumps 

The screw centrifugal pump provides yet another example of a technology finding applications in sectors for which it wasn’t originally developed and one where the higher initial investment is more than offset by the economics of its longer-term reliability and aptitude to a good job. 

In any pumping application, it is always necessary to match the pump type to the application in order to achieve to desired result. One aspect of the selection process is matching the fluid transfer mechanism to the nature of the fluid being pumped. Where sensitive fluids, low and high viscosity fluids require pumps that can run efficiently at low and high flowrates across a broad pressure range Twin, Triple and Multi-Screw Pumps have the answers and AxFlow has the technologies. 

Why buy screw pumps from AxFlow? 

AxFlow provides screw pumps that cater to an extensive variety of industries and applications. Exclusive to AxFlow, you will be provided with personalized recommendations from highly experienced process engineers, and access to the most prominent process technology manufacturers that are independent of the manufacturer. If you require assistance in selecting the appropriate pumps that satisfy your requirements, feel free to contact AxFlow without any delay. AxFlows engineers and specialists can help with the selection process, specifications, installation, and maintenance of your fluid handling equipment.