Air Diaphragm Positive Displacement Pumps. These positive displacement pumps use the reciprocating action of a flexible diaphragm to pump a fluid. Diaphragm pumps are defined by the manner in which the diaphragm is flexed. The air diaphragm pump has its diaphragm flexed by variations in air pressure. When the diaphragm moves up, the pressure in the chamber decreases, and fluid is drawn into the chamber. When the diaphragm moves down, the pressure increases and fluid is forced out of the chamber.
Things to Consider: Application, Wetted materials, Maximum flow rate, Flow range, Maximum pressure, Temperature range, Port size, Self-priming capability, Particulate handling capability, Run dry capability, Dimensions, Weight, Duty cycle, Power requirements, Fuse requirements, Agency approvals, Warranty.
Drum Positive Displacement Pumps. Also called barrel pumps, these positive displacement pumps extract fluids from storage barrels. They are available in both hand-operated and motor operated configurations.
Things to Consider: Material, Tube diameter, Length, Seal, Shaft, Internals, Hose size, Weight, Maximum fluid specific gravity, Maximum temperature, Maximum viscosity, Maximum head, Motor certification, Motor electrical requirements, Motor power output, Motor rpm, Motor weight, Warranty.
Gear Positive Displacement Pumps. These pumps are fixed displacement, meaning they pump a constant amount of fluid for each revolution. They are one of the most commonly used pumps for hydraulic fluid power applications. There are two main variations: external gear pumps which use two external spur gears, and internal gear pumps which use an external and an internal spur gear. As the gears rotate they separate on the intake side of the pump, creating a void and suction which is filled by fluid. The gears move the fluid to the discharge side of the pump, where the meshing of the gears displaces the fluid.
Things to Consider: Size, Maximum capacity, Maximum viscosity, Maximum pressure, Minimum and maximum temperatures, Materials of construction, Warranty.
Metering Positive Displacement Pumps. These positive displacement pumps move liquids at adjustable flow rates which are precise when averaged over time. Metering refers to this process, and refers to the pump’s application, rather than the kind of pump used. Positive displacement pumps are often used as metering pumps to pump chemicals, solutions, or other liquids, and are able to pump into a high discharge pressure. These pumps are commonly driven by an electric motor.
Things to Consider: Application, Fluid type, Maximum flow rate, Speed control, Motor size, Motor power requirements, Motor RPM, Construction and materials, Belt drive versus direct drive, Forward/brake/reverse capability, Explosion proof system if required for application, Dimensions, Weight, Warranty.
Peristaltic Positive Displacement Pumps. These positive displacement pumps move fluids through a flexible tube fitted inside the pump casing. A turning rotor/cam with rollers attached to its outer circumference, compresses the tube, forcing the fluid to move through it. When the rotor/cam lifts the rollers from the tube, it re-opens, and fluid flow is induced to the pump. This process is called peristalsis. The tube prevents fluids from contaminating or being contaminated by the pump.
Things to Consider: Application, Maximum working pressure, Maximum fluid temperature, Ambient temperature range, Enclosure (NEMA rating), Pump tube material, Duty cycle, Maximum solids (% by volume), Maximum viscosity, Maximum suction lift, Turn down ratio, Power requirements, Variable speed, Dimensions, Weight, Tube connection, Pump tube OD, Maximum feed rate, Maximum strokes/minute, Warranty.
Progressive Cavity Positive Displacement Pumps. Also known as a progressing cavity pump or eccentric screw pump, these pumps transfer fluid through a sequence of small, fixed shape cavities that progress through the pump as its rotor is turned. Flow rate is proportional to the rotation rate. These pumps can pump at extremely low rates, even to high pressure.
Things to Consider: Dimensions, Port sizes, Materials of construction, Motor power requirements, Motor rpm, Weight, Fluid viscosity, Flow versus discharge pressure curve, Power versus discharge pressure curve, Warranty.
Rotary Lobe Positive Displacement Pumps. These positive displacement pumps can handle solids, slurries, pastes, and a variety of liquids. Rotary lobe pumps use rotating lobes to push material through the pump. They offer continuous and intermittent reversible flows, and can operate dry for brief periods of time. Because the lobes do not make contact, particle size pumped can be much larger in lobe pumps than in other positive displacement types.
Things to Consider: Application, Maximum flow, Maximum head, Maximum power, Maximum working pressure, Temperature range, Speed range, Materials of construction, Maximum viscosity, Sanitary 3A rating, USDA rating, Solids range (maximum diameter), Seal configurations, Flanges available, Suction and discharge sizes, Displacement per revolution, Maximum capacity, Dimensions, Weight, Warranty.
Sanitary Positive Displacement Pumps. The characteristic that differentiates sanitary pumps from other positive displacement pumps is that they require extreme levels of cleanliness. They require special construction materials and have stringent cleaning requirements. Costly corrosion-resistant materials and special finishes are required for product contact areas, which must be cleanable and smoothly polished. Quick-change fasteners, flanges, and gaskets are used to simplify disassembly for cleanup. Components must be rugged to withstand repeated disassembly for the cleanup procedure.
Things to Consider: Discharge rate, Working pressure, Fluid viscosity, Maximum and minimum temperatures, Inlet/outlet port sizes, End connections, 3-A compliant clean-in-place design, Dimensions, Weight, Warranty.
Special Positive Displacement Pumps. These pumps, while operating on the same principles as all positive displacement pumps, are manufactured using materials, hardware, finishes, coatings, or processes that are required by specific, non-traditional design applications.
Things to Consider: Maximum discharge pressure, Maximum discharge flow, Inlet size, Discharge size, Media temperature, Power source, Application, Pump type, Adjustable speed feature, Belt driven feature, Continuous duty feature, Corrosion resistant feature, Pressure gauge equipped, Portability, FDA rating, USDA rating, 3-A rating, Materials of construction, Dimensions, Weight, Warranty.
