Positive displacement pump types include: gear, lobe, piston, diaphragm, peristaltic, screw, progressive cavity, hydraulic and many others. Their advantages are:
Positive Displacement pumps operate by using a rotary, reciprocating, or diaphragm method of drawing fluid into the pumping chamber at the inlet and pushing it through a discharge outlet. Positive Displacement pumps move fluid at a constant rate regardless of pressure conditions, and they are typically the preferred choice for low to moderate flow rates at higher discharge pressures.
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Viking Pump Internal Gear – Cutaway
Wilden Air Operated Double Diaphragm Pumps
Liquiflo Centrifugal Pump Selection
A Liberty Process progressive cavity pump is used when the pumping application is not suited to a centrifugal pump. This includes:
A Liberty Process progressive cavity pump ideal for liquids with higher viscosities or thickness. A progressive cavity pump will have about the same flow for any liquid viscosity. The mechanical efficiency and volumetric efficiency goes up when the viscosity increases, with lower power and more flow. If you have a pumping application where you need a constant flow, but the liquid viscosity is variable and will change, then the PC pump is an ideal choice.
A progressive cavity pump is good when the application requires a varied flow. A progressive cavity pump has a precise flow per revolution of the pump. It is therefore quite easy to regulate the pump flow by just simply regulating the pump speed. Modern pump speed controllers like variable frequency drives (VFD’s) are well suited to be used with progressive cavity pumps for varying pump speed and flow control.
Another good application for a progressive cavity pump is when the suction conditions of the pumping applications are not ideal. A progressive cavity pump requires much lower Net Positive Suction Head (NPSH) as compared to a centrifugal pump because the internal pump velocity is lower. A progressive cavity pump can pump when the suction pressure is as low as 28″ of mercury (Hg), a centrifugal pump cannot do this. A progressive cavity pump will easily fill and pump in difficult applications when a centrifugal pump will not.
Progressive cavity pumps are ideal for applications where the liquid is sheer sensitive again because of lower internal velocity. A good example would be pumping oil and water mixtures to separation devices. The separation device works much better when the oil droplets are larger. A progressive cavity pump will not change the oil droplets where a centrifugal pump will emulsify the oil and make the oil droplets very small and reduce the separation performance of the separator.
A progressive cavity pump is good to use when the liquid contains abrasive solids. Most other types of positive displacement pumps can’t pump solids very well or for very long due to their close tolerances and all metal designs. A gear pump or vane pump will simply wear out when solids are present in the liquid and the same would also happen to most centrifugal pumps and they could clog. A progressive cavity pump is designed to last longer than all other pumps on abrasive applications. The pump design with the rotor and stator is the heart of the pump design for abrasion resistance. The internal velocity of the liquid as it travels through the pump is much lower than other types of positive displacement pumps and centrifugal pumps and the rubber stator.
Neptune diaphragm metering pumps are used for reliable chemical dosing for almost any industry and are available for high and low pressure applications with manual and electronic stroke control for precise product metering. Additional accessories from Neptune include mixers, injection quills and sample coolers, just to name a few.