How Do You Know When Your Application Requires a Twin Screw Pump?

Did you know that there are many different types of pumps associated with sanitary processing systems?

In these systems, plant engineers and managers use pumps to move product through the process pipelines, to empty or fill storage tanks or vessels, and in clean-in-place (CIP) operations to pump rinse and cleaning solutions through the processing system to thoroughly clean it, and ensure that it continues to meet hygienic standards.

CSI represents several different pump suppliers and uses their products in the sanitary processing systems that we design, build, and install for our customers.

This article will give you an overview of the OS Series Twin Screw pump from Alfa Laval to help you determine when to specify this CIP and product transfer pump.

The following paragraphs will review what a screw pump is, how it is used in sanitary processing applications, and the unique features and benefits of the Alfa Laval Twin Screw pump.

Alfa Laval OS Series Twin Screw Pump
Alfa Laval OS Series Twin Screw Pump Opened

What is a screw pump?

Screw pumps, also called water screws, are positive-displacement type pumps that use one or more screws to move liquids or solids along the screw(s) axis. By design, they are coupled, with the motor directly connected to the input shaft of the pump.

The Twin Screw pump can be configured so that either port can be the inlet or outlet. This should be specified at time of order. Unlike other style of screw pumps there is not contact between screws or screw or screw to pump casing resulting in long life and a fully hygienic and cleanable design. The only contact within the product is the mechanical seal faces and if applied correctly will also result in a long life of the seal.

Advantages

In comparison to centrifugal pumps (which use impellers to move water or other fluids through the pump), positive-displacement screw pumps offer several advantages:

  1. The pumped fluid is moved axially, reducing turbulence and pulsation resulting in very low damage to pumped product. This design feature makes these types of pumps easier on product than centrifugal-style pumps.
  2. Screw pumps can pump fluids of significantly higher viscosity than centrifugal pumps.
  3. Changes in pressure differential have little impact on the flow rate of positive-displacement pumps compared to centrifugal pumps when pumping viscous product.

Disadvantages

In comparison to other types of pumps, however, twin screw pumps have a couple of disadvantages:

  1. Twin screw pumps are relatively expensive to purchase. In applications where a diaphragm or lobe-type pump is already working well, a twin screw pump is not a cost-effective solution.
  2. To accommodate both process and CIP applications, twin screw pumps need to use larger motors than other types of pumps. A good rule of thumb for sizing a twin screw pump for a dual-use application is to use the same horsepower motor as one would use for a CIP supply pump.
  3. Due to their complexity compared to other types of pumps, twin screw pumps may have additional maintenance requirements.
As is the case with most useful tools, correctly applying a twin screw pump to a specific application is paramount to successful operation. If you have issues with NPSH (net positive suction head), entrained air in your product, are pumping large solids, or are concerned about line pulsation, then a sanitary twin screw pump may be a product worth considering.

The OS Series Twin Screw Pump from Alfa Laval

CSI supplier Alfa Laval is a Swedish company founded in 1883. The company’s products are used to heat, cool, separate, and transport various materials, including oil, chemicals, water, beverages, food, starches, and pharmaceuticals. Alfa Laval is a premier supplier of the hygienic pumps and mixers used in CSI’s process systems.

The Alfa Laval OS Twin Screw pump operates on the following principle. As the pump runs, the inter-meshing of the pump’s counter-rotating screws, along with the pump’s housing, form volumetric chambers. These chambers fill with the fluid being pumped from the inlet and move it axially from the pump's suction side to the higher-pressure outlet (or discharge) side of the pump.

Common process media transported through a twin screw pump include:

  • Guacamole
  • Sour cream
  • Yogurt
  • Cheese
  • Salsa
  • Salad dressing
  • Aloe vera
  • Lotion
  • Shampoo
  • Yeast 
  • Hops

Advantages

  1. Low shear twin screw pumps handle large solids well and are also excellent at pumping products with entrapped air (i.e., trapped air bubbles).
  2. Excellent for handling sensitive and abrasive materials, as well as both high and low viscosity fluids.
  3. These types of pumps can handle a wide range of flows and pressures.
  4. With proper seal quench, twin screw pumps can run when dry.
  5. Twin screw pumps are true dual-duty pumps. When properly sized, these pumps can serve not only to move process fluids, but may also be used as fluid return pumps for CIP operations, eliminating the need to purchase multiple pumps in a dual-purpose process line. This approach also simplifies piping layouts and pump controls, and minimizes contamination issues.
This pump is a versatile workhorse that is designed for applications in the dairy, beverage, and food processing industries where cleanability is paramount.

Smooth and gentle in operation, with low pulsation characteristics and excellent solids handling capabilities, the OS Twin Screw pump reduces the potential for product damage.

This is also a truly hygienic pump, industry-certified to both 3-A and EHEDG standards. To this end, the OS Twin Screw is constructed using FDA conforming materials, with a clean stainless-steel exterior finish and profiled elastomers. The pump’s mechanical seals are always fully surrounded by the pumped fluid.

    In terms of performance, the OS Twin Screw pump provides superior suction, making it ideal for emptying totes, IBCs, and static suction vessels.

    The pump is also engineered for both long service life and reliability, as evidenced by the following:
    • The unique front loading cartridge seal allows quick, easy seal replacement with the pump in place and is made possible with a truly front-loading, self-setting design. The unique cartridge is a pre-assembled complete seal that simply plugs into the pump without need to remove the pump casing. This feature maximizes process uptime and minimizes maintenance costs.
    • A sturdy, all-stainless-steel gearbox features timing gears located between the bearings for an optimal bearing span. This design provides a balanced loading of the shaft assembly, reducing vibration and noise and increasing component life and reliability.
    • The oil chamber design provides enhanced lubrication of the bearings and gears, minimizing gearbox running temperature and increasing bearing life.
    • Timing gears are easily accessed while the pump is in position. This simplifies the process of screw retiming without the need to drain the gearbox oil or remove the coupling and the motor.

    The Alfa Laval OS Series Twin Screw pump is available in a variety of configurations:

    1. Single, single flush, or double sealing front seals may be fitted. 
      1. The option of single flush resolves issues like dry running and pumping sticky product, however, much more cost effective than a full double seal.
    2. Three different screw profiles may be specified to suit differing applications.
    3. The pump is available in nine different models, based on three different frame sizes.

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    Next Steps

    The Alfa Laval OS Twin Screw pump is an ideal choice for hygienic processing applications. The OS reliably pumps both high and low viscosity fluids with minimal product damage, as well as CIP fluids. This pump’s robust and reliable design reduces the overall cost of ownership and increases process uptime. 

    Superior suction performance with excellent lift capability and low NPSHr (net positive suction head required) provide flexibility in installation and increase product recovery. And, the combination of an optimized gearbox design and excellent hydraulic performance in the OS provides for quiet pump operation, minimizing noise emissions.

    Contact your CSI Pump Solution Center Expert at (417) 831-1411 to learn more about the Alfa Laval OS Twin Screw pump and how it might fit your particular application.

    Contact CSI

    ABOUT CSI

    Central States Industrial Equipment (CSI) is a leader in distribution of hygienic pipe, valves, fittings, pumps, heat exchangers, and MRO supplies for hygienic industrial processors, with four distribution facilities across the U.S. CSI also provides detail design and execution for hygienic process systems in the food, dairy, beverage, pharmaceutical, biotechnology, and personal care industries. Specializing in process piping, system start-ups, and cleaning systems, CSI leverages technology, intellectual property, and industry expertise to deliver solutions to processing problems. More information can be found at www.csidesigns.com.

    Alfa Laval Master Distributor

    About Alfa Laval

    Central States Industrial (CSI) is a master distributor of Alfa Laval sanitary equipment and their Tri-Clover® product range. Alfa Laval is a leading global supplier of products and solutions for heat transfer, separation, and fluid handling through their essential products: heat exchangers, separators, pumps, valves, and fittings.

    The Alfa Laval name has long been recognized as a supplier of high-quality products. While quality remains a top priority, their mission is to provide value to customers by optimizing the performance of your processes. With more than 2000 patents, they offer worldwide solutions in areas that are vital to society both today and for the future. Their products are used in a wide variety of industries, including the manufacturing of food, chemicals, pharmaceuticals, starch, sugar, and ethanol.