Positive displacement type pumps are available for various use. There is a cavity in the positive displacement pump. It sucks the known amount of fluid in the pump cavity during suction stroke. These pumps displace fluid out of the pump cavity during the discharge stroke. Positive displacement type pumps have a moving element that displaces the fluid. The moving element of the positive displacement type pumps can be a plunger, piston, diaphragm, screw, and a flexible polymer tube. Depending on the constructional features and their applications, positive displacement pumps are categorized as follows:
(1) Rotary lobe pumps.
(2) Progressive cavity pumps.
(3) Rotary gear pumps.
(4) Plunger/ Piston pumps.
(5) Diaphragm metering pumps.
(6) Screw pumps.
(7) Peristaltic pumps.
(1) Rotary Lobe Pump
Rotary lobe pumps are positive displacement type pumps. They have large pumping chambers that enable them to handle solid material like cherries and olives without damaging their physical structure. Rotary lobe positive displacement pumps are also used to handle slurries, paste, used in the dairy and beverage industries. It maintains the integrity of the product without contamination. Positive displacement pumps are smooth moving without degrading the fluids. They are mainly used in food, pharmaceutical, and process industries, where contamination in the process is not permissible.
(2) Progressive Cavity Pump
Progressive cavity pumps are positive displacement type pumps. They are consist of two parts rotor and stator. The rotor is made from a solid alloy steel bar stock. It is made in a single helix form. Another part of the pump is the stator which is usually made from nonmetal elastomer. It is having a double helix cavity.
The rotor of the pump seals tightly against the stator cavity when it rotates. The fluid sucked in the stator cavity is conveyed by a rotor screw to the discharge port of the pump. Progressive cavity displacement pumps are valve-less. Due to their high process reliability and suction capacity, they are used for the continuous smooth flow and precise dosing of the difficult fluid. Progressive cavity positive displacement pumps are used for the following applications:
(1) With and without solid content fluids.
(2) Low to high viscosity fluids.
(3) Thixotropic, and dilatant fluids.
(4) Shear-sensitive fluids.
(6) Non-lubricating and lubricating fluids
(7) Aggressive fluids
(8) Adhesive fluids
(3) Rotary Gear Pump
Rotary gear pumps are, (1) internal gear type and (2) external gear type. Both are positive displacement type pumps. The internal gear pump consists of a rotary and idler gear assembly. They generate the flow as the rotary gear moves the idler gear. The space created by the crescent offsetting the gear and the meshing teeth of the idler gear displaces the fluid and pushes it to the discharge port. Internal gear pumps are used in the application for small closed places. Due to their very low noise level and smooth running, they are used in hydraulic fluid power applications.
(4) Reciprocating Plunger/Piston Pump
A reciprocating pump is a positive displacement type pump. It uses a backward and forward movement of the plunger or piston to move the fluids. The backward movement of a plunger or piston sucks the fluid into the pump cylinder. The forward movement of the plunger or piston discharges the fluid out through the discharge port of the pump.
A fixed volume of the fluid is discharged in each stroke of the pump. Mainly the pumps are used for high-pressure discharge into closed pressurized systems. They are used in all fuel injection applications of engines. High-pressure dosing of ingredients in pharma industries, high-pressure dosing of chemicals for water treatment is carried out with these pumps. They are used for high-pressure cleaning of heat exchangers, in petrochemicals and refinery plants.
(5) Diaphragm Metering Pump
Diaphragm Metering Pumps are the positive displacement type pumps. They are used to avoid leakage of the fluid through the pump shaft packing. They are used specifically when a fluid is inflammable, toxic, noxious, and precious. Diaphragm metering pumps are used for handling fluids where precise metering of the fluid is required.
Diaphragm metering pumps are used to feed high-pressure fluid into closed pressurized systems. Diaphragms of the pumps are actuated by the hydraulic fluid pressure. On one side of the diaphragm, there is the hydraulic fluid and on the other side of the diaphragm, the actual fluid that is to be pumped. These pumps are used in chemical, refineries, and petrochemical plants, where precise metered fluid handling to be carried out, without contamination.
(6) Screw Pump
A screw pump is a positive displacement type pump. It is also known as a water screw pump. It is used to lift water from water sumps. The screw pump may have one or many screws in the pump housing. They handle fluids or solids along the screw axis. In a single screw, the pump screw rotates in the cylindrical cavity and thereby moves the fluid to discharge through the discharge port.
Multi screw pumps are also positive displacement pumps. The screw rotor meshes in such a way that forms the cavity in between the screw teeth and housing. The screw pump rotor rotates the fluid to enters from the suction side of the pump. Fluid moves linearly and messing screw rotors convey the fluid to the discharge port of the pump. The clearance between the screw and the liner is very small so fluid pressure is built up when it is discharged through the pump.
Positive displacement Screw Pumps are used for the following applications:
(1) lubrication services
(2) Seal oil services
(3) Power hydraulics
(4)Machines, dumping equipment, elevators, hydraulic winches
(5)Food chocolates, syrups, vegetable oils
(7) Petroleum plants
(8) Fuel burners
(7) Peristaltic pump
A peristaltic pump is a positive displacement type pump. They are used for pumping various fluids. They are also commonly known as roller pumps. The fluid is sucked in a flexible tube fitted inside a circular pump casing. The roller assembly rotates and squeezes the fluid at the suction of the pump and pushes the fluid to the discharge side of the pump. Positive displacement Peristaltic pumps are used for:
(1) pizza, sauce dispensing
(2) juice production,
(3) injection of vitamin A and D.
(4)cell suspension in fermentation.
Positive displacement Peristaltic pumps have many industrial uses. They are used in R and D set-ups, where the contamination of the fluid is not permissible. The fluid does not come in contact with the pump parts and the pump parts do not come in contact with the fluid. In the peristaltic pump, the fluid is handled by squeezing the flexible polymer tube with the help of rotating rollers, hence the contamination of the fluid is eliminated. The main parts of a positive displacement peristaltic pumps are:
(2) roller Assembly
(4) pump housing
(8) Deep well hand Pump
A deep well hand pump is the positive displacement type pump. It is one of the essential pumps in a rural area. When the weather is stormy and power failures occur in rural areas, there is no water for drinking, cooking, washing, and toilet flushing. A new breed of deep-well hand pumps has eliminated this eventuality. A positive displacement deep well hand pump can lift the water from about 80 meters in depth. A positive displacement hand pump is serving the large population of rural India for their water need.