Positive Displacement Pumps and Applications

Positive displacement pumps or PD pumps are one kind of pump and the designing of these pumps can be done long before centrifugal pumps. The fluid is positively moved from a set quantity container. These pumps are competent in expanding high pressures while working at little suction forces. These pumps are commonly called as constant volume pumps. The capacity of these pumps is not affected by the force not like to centrifugal pumps. Generally, liquid flow can be regulated by changing the speed of the pump. This article discusses an overview of what is positive displacement pump, working, types, and applications.

What is Positive Displacement Pump?

The PD pump or positive displacement pump provides an estimated stable flow at a speed, although changes within the counter force. The action of the pumping of the pump is cyclic which can be motivated by screws, pistons, rollers, gears, diaphragms or vanes.

The positive displacement pump working is, the moving of liquid in this pump can be captured inside a cavity to discharge the set quantity of liquid. The liquid dislocation can take place with a few parts namely piston, diaphragm, and plunger. At the side of suction, the pumps have an increasing cavity as well as a reducing cavity at the side of discharge. Because the fluid can be sucked on inlet side while the cavity increases & releases it whenever the cavity reduces.

positive-displacement-pumps
positive-displacement-pumps

Types of Positive Displacement Pumps

The positive displacement pump types are three namely: rotary pumps, reciprocating pumps, and linear pumps.

types-of-positive-displacement-pumps
types-of-positive-displacement-pumps

Rotary Pumps

In rotator type pump, the liquid can be supplied using a rotary, and its rotation moves the liquid from the lake to the releasing pipe. The best examples of these pumps mainly include screw pump, internal gear, flexible impeller, sliding vane, helical twisted roots, circumferential pump, etc. These pumps are classified into three types namely gear pumps, screw pumps, and rotator vane pumps.

  • In gear pumps, the liquid can be moved among two rotating gears when it rotates.
  • Screw pumps include two screw form rotor which turns against each other. Once the two screw turns, then it sucks the liquid from the inlet of the pump to the outlet of the pump.
  • Rotary vane pumps are like scroll compressors which include cylindrical rotor with vanes over it. It is covered within a cylindrical shaped housing. Once it turns, the vanes on top of the rotor catch the liquid among the rotor & casing, and the liquid discharges through the outlet.

Reciprocating Pumps

In reciprocating pumps, the division of reciprocating assists the liquid to flow forward from the lake. The reciprocating parts of these pumps are a plunger, a piston otherwise a diaphragm. This type of pump includes different types of valves such as the inlet valve and outlet valve. In the fluid suction method, the inlet valve opens & the outlet valve stays closed.

When the piston turns in the right direction, then the cavity of the pump increases, as well as the liquid, can be sucked into the cavity. These pumps are classified into three types namely plunger pumps, piston pumps, and diaphragm pumps.

  • The plunger pumps are mainly used for pushing water.
  • The piston pump is inbuilt with a piston which is used for pumping the liquid
  • The diaphragm pump works similar to plunger pump however it includes diaphragm for suction & expulsion of liquid.

Linear Pumps

In linear pumps, the dislocation of the liquid takes place in a straight line which means linearly. The best examples of these pumps are rope pumps as well as chain pumps. In this type of pump, the calibration cannot be needed. This type of pump can be placed within a static location. But, the main issue of this pump is volume. Because of the piston withdrawal within the cavity, these pumps will make a lot of sounds and therefore, must be fixed distant from living places. These pumps are classified into two types namely rope pump and chain pump

A rope pump is one type of linear pump wherever a loose hanging rope is placed into a well & drawn up with the help of a lengthy pipe where the base immersed within water. The round disks are attached on the rope, which will draw the water in the direction of the outside. This kind of pump is frequently used for both self-supply & community supply of water. These pumps can be fit on boreholes otherwise hand-dug wells.

The chain pump is one type of linear pump where a number of circular discs are located on a continuous chain. One division of the chain is immersed into the water, & the chain runs throughout a pipe, somewhat superior to the disc diameter. Once the chain is drawn up the pipe, then the water turns into trapped among the discs and is discharged at the summit. These pumps are used for centuries during the early Middle East, China & Europe.

Difference between Positive Displacement & Non-Positive Displacement Pump

The difference between positive displacement and non-positive displacement pump mainly include pressure, efficiency, viscosity, performance, etc.

Parameters

Positive Displacement Pump

Non Positive Displacement Pump

Pressure

These pumps work for high force applications, and the force might be 800 bar.

These pumps are used for low force applications and the pressure might be 18 bar to 20 bar.

 

Efficiency

When pressure increases then the efficiency will automatically increase.

The efficiency will decrease at a lower pressure or higher pressure.

Viscosity

When the viscosity increases then efficiency will increase because of the frictional losses in the pump

When the viscosity increases then efficiency will decrease because of the frictional losses in the pump

Performance

When the pressure changes then the flow will change

When the pressure changes then the flow will constant

Applications of Positive Displacement Pumps

These pumps are commonly used to pump high viscosity fluids where precise dosing otherwise high force output can be necessary. Not like centrifugal pumps, the outputs of these pumps are not affected by force thus they also have chosen in any condition where the supply is unequal. The best positive displacement pump examples are piston, plunger, diaphragm, gear, lob, screw and vane.

  • Piston and Plunger pumps are used to pump low viscosity fluids, paint spraying, oil production, and high force washing.
  • Diaphragm pump can be used for metering, spraying, treatment of water, oils, and paints.
  • Gear pumps are used for pumping the high viscosity fluids within the petrochemical, food industries, paints, oils, etc.
  • Lobe pump is used in food and chemical industries pharmaceutical, biotechnology, sanitary, etc.
  • Screw pump is used in fuel transferring, production of oil, irrigation, etc
  • Vane pump is used in low viscosity liquids, fuel loading, & transmission, etc.

A positive displacement (PD) pump is used to move a liquid frequently with a set volume, with the help of valves otherwise seals by moving it automatically throughout the system. The action of pumping is repeated & can be driven by screws, pistons, lobes, gears, vanes, diaphragms. These pumps are mainly used where highly viscous fluids are required. Here is a question for you, what are the advantages and disadvantages of positive displacement pumps?

 

 

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