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

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.