Progressive Cavity Pumps
What is a progressive cavity pump?
Progressive cavity pumps are known for their ability to handle difficult liquids containing solids and highly viscous liquids. Also known as a single screw pump, the progressive cavity pump uses a single threaded screw or rotor rotating inside a double threaded rubber stator to move liquid through the pump and build pressure to move liquid through the system.
How do they work?
The pump rotor is shaped like a rounded helically shaped screw, rotating with an interference fit inside a rubber stator which is also helically shaped. As the rotor turns, the helical shape of the rotor and stator create a cavity that moves or progresses along the length of the stator as the fluid is drawn through. The effect of this design is that the fluid is moved at a very predictable and steady rate, but it exits the pump with high pressure. This makes the pump ideal for systems in which a consistent amount of high-pressure fluid is needed at the outlet.
A progressive cavity pump is able to generate about 75 psi of pressure at the discharge, but multiple rotors and stators can be connected in series to achieve higher pressures. The rotor design makes this pump type somewhat longer than other rotary positive displacement pump types. Since there must be enough room to pull the rotor out of the stator for maintenance, the floor space required for this pump type is greater than for other rotary PD pump types. Also, since the rotor has an interference fit in the rubber stator, the starting torque for this pump is quite high, and the motor must be carefully sized to handle the start-up torque.
Where are progressive cavity pumps used?
They are useful in a wide variety of industrial and wastewater treatment applications. Smaller-scale pumps are used for oil lubrication systems and hydraulic actuated elevators. Larger types are used for pumping sewage sludge, slurries, oil, and other viscous chemicals. Because of their ability to move hard-to-handle liquids, and in consideration of their relatively high cost and large floor space requirements, the progressive cavity pump is sometimes thought of as the pump of last resort, when nothing else will work.
KNOLL America features its MX series progressive cavity pumps for the pharmaceutical, food and beverage, and chemical industries. The sanitary pump can accommodate flow rates to 400 gpm and max pressures to 145 psi, per pressure stage. The MX pump is able to plasticize block goods as well as pump soft pieces such as strawberries or cheese curd without damage or deformation.
The NETZSCH NEMO progressive cavity pump series is designed to handle difficult pumping applications that often involve abrasive and viscous fluids involving solids. To fit a wide range of applications, each NEMO pump can be assembled with the customerís choice of various materials of construction. The progressive cavity pump has low noise levels, is self-priming, and allows for max flows to 2,000 gpm at 350 psi.
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