Why progressive cavity or screw pumps are no match for electric diaphragm pumps

Progressive cavity pumps or screw pumps have limited material/application compatibility with fluids and involve significant maintenance costs due to their complex mechanical seals. Graco’s QUANTM electric operated double diaphragm (EODD) pumps offer a forgiving and flexible alternative with a non-rotating and seal-less design.

Progressive cavity (screw) pumps

Because of their steady flow and resistance to high temperatures, progressive cavity pumps (screw pumps) are used in a wide variety of industries and applications. However, they suffer from certain key disadvantages that can lead to frustrating downtime, expensive repairs, and even product replacement.

• Troublesome mechanical seal
  The lionshare of progressive cavity pump drives transmits their power to the internal screw through the pump casing using a rotary shaft seal. This mechanical seal is an expensive wear part and is sensitive to increased heat, abrasives, and non-lubricating liquids, which increases  the risk of leakages over time. Furthermore, the mechanical seal itself raises sanitation/contamination concerns in hygienic industries like food/personal care processing and is costly to repair. Finally, and possibly most important of all, the material being pumped can be altered by the force of rotation and friction of the shaft and seal, further heating the liquid.

• Unable to run dry
  Progressive cavity style pumps cannot run dry without destroying expensive stators and rotors. The material/fluid being pumped always has to be present to lubricate the contacting surfaces between rotor and stator. In fact, running dry is the most common failure of this pump technology. In food and beverage manufacturing applications in particular, additional sensors monitoring the availability of material at the pump inlet can create more potential leak paths and points of bacteria growth in the system.

• Large footprint
  Because of their intricate design, progressive cavity pumps take up a lot of space, particularly when it comes to higher flow rates. The motor, pump housing, and the “Progressive Cavity” itself physically require space that can’t be designed out of the system.

• High energy consumption
  When it comes to operating costs, these pumps are expensive to run. Due to high friction resistance, they have a high energy consumption, and spare parts are expensive.

• Not suitable for pumping abrasives
  When pumping chemical fluids or fluids with a highly abrasive content, a cavity pump’s stators and rotors will quickly wear out and will need to be replaced. Some fluids also cause the elastomers in the stators to swell. Moreover, replacement of the rotor or stator is a difficult and lengthy process.