There are a bewildering range of process pumps that are commercially available today and some have been in existence not long after the advent of the practical electric motor to drive them. There are now centrifugal pumps that make up the vast majority of mass flow pumping requirements for fluids, slurries and liquefied gasses. These pumps are usually axially driven, with or without a gearbox, by a three-phase or single phase electric motor.
The variations on a centrifugal pump are quite wide, but all feature fluid being delivered by an inlet pipe to the centre of an impeller, usually rotating at 1415 rpm (if not geared) within a shaped body, and the fluid being delivered at high pressure tangentially to a outlet pipe. The actual design varies markedly depending on the application but the shaped body and impeller are quite distinctly shaped.
Some of the variations of the centrifugal pump is the mag drive pump. This is often found in processing plant where high viscosity fluids are being pumped or where there is a need to avoid shock loading for variable-speed operation. They are also specified where there is a need to physically separate flammable, toxic or 'clean' fluids from both the environment and the sparks from the electric motor. Magnetic drives are also used for turbine and vane pumps in the food industry.
There are a whole range of 'hygienic' liquid processing applications based of the centrifugal pump and the applications for the food and beverage industries feature stainless steel construction for effective cleaning and are used for transferring non-fragile (high shear) water or water-based products for clean-in-place (CIP) processes.
Then there are a whole range of positive displacement pumps making up most of the remaining types of process pump available to the processing industries. The principle of the positive displacement pump is that they transfer the fluid in discrete packets from pump inlet to discharge. This can be by means of a reciprocating (piston) action such as the diaphragm or piston pump or the progressive cavity pump such as the lobe, screw or peristaltic pump.
The chief characteristic of the family of positive displacement pumps is that they all transfer fluid at a constant rate for a given motor speed irrespective of external hydraulic influences. This is in complete contrast to the centrifugal pump that can continue to rotate and using energy under 'closed valve' conditions on the delivery side. This translates to a maximum delivery head. This feature for positive displacement pumps makes them ideal for metering known flows such as for chemical dosing and food product mixing and pharmaceutical applications.
Another main characteristic is that the positive displacement pump family is that they can deliver at higher pressure and at greater efficiency of the centrifugal pump which is handy in extreme operating pressures such as in petrochemical cracking plants for dosing of mixing from a low-pressure source vessel without resorting to lower efficiency multi-stage centrifugal pumping arrangements such as the ubiquitous mono type pump. In more mundane environments like workshops, small food processing plants and many field operations, piston pumps such as found in barrel pumps can transfer fuel, oils and other fluids quickly and cleanly.
The peristaltic pump, a form of progressive cavity pump, deserves some further mention in that they are perfect shear sensitive, delicate liquids containing solids, they have no glands, valves or any moving parts in direct contact with the fluid being pumped. They are thus versatile in use and can be found delivering blood products at low pressure intravenously, metering small doses of reagents in a laboratory experiment, as food pump devices delivering yeast culture to dairy product manufacture or at the other end of the scale, delivering 20,000 litres per hour at 15 bar delivery pressure.