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types of positive displacement pumps , is very important for chemical engineers. IN this article we will cover what is positive displacement pump ? what are the different types of pumps ,positive displacement pumps examples, positive displacement pump definition application ,positive displacement pumps examples classification of pumps , gear pumps , reciprocating pumps ,all pumps. Pump definition.

Positive Displacement Pump

Positive displacement pump is used for handling of slurry and viscus liquid. As we study in article of different types of centrifugal pumps , centrifugal pumps is used for high flow requirement ,positive displacement pumps are used for high pressure requirements.

In thus types of pumps ,a fixed volume or constant volume of liquid is pumped. In this type of pump there is expanding cavity on suction side and decreasing cavity on discharge side.

This type pump is not suitable for liquid with requirement of high volumetric flow rate .

When we choose a positive displacement pump ?

if your requirement is high pressure ,high viscosity , slurry type fluid ,liquid with solid content, semi-liquid then you can choose a positive displacement types of pumps Chemical Engineer Online

Types of positive displacement pumps

There are main two types of positive displacement pumps ,

Reciprocating Pump

Rotary Pumps

Reciprocating pumps

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Reciprocating pumps are the pumps which contains a plunger or a piston in a cylinder. The main component of a reciprocating pump is piston. In this types of pumps , a fixed volume is get discharge one each stoke of piston or on each stoke of plunger. We can adjust the flow rate of this pump by setting the number of piston per minutes . This pump can use for oil , diesel and viscus fluid .

Rotary Pumps

Rotary pumps are also widely used for special application in chemical industry . Like transfer of slurry .This pump deliver a fixed volume per revolution . we can set our desired flow by setting the revolution number per minutes .We need to calibration for confirmation of fixed volume of a rotary pump. In this types of pumps the main parts are , gears , vanes , lobe and casing etc. when we start a rotary pump , a rotating element pushed the fluid in to the casing then fluid go out from the discharge .

As we know that this is pressure pump , it can generate pressure on discharge if discharged valve is closed , so this type of pumps always need a pressure relief valve on its discharge . This are the main types of positive displacement pumps.

Gear Pumps

Gear pumps are typical types of positive displacement pumps. This types of pumps use gear to transfer the fluid. Gear pump contains a set of hear in it body which movement transfer the fluid. This types of pumps mostly used for pumping a very high viscus fluid in chemical , pharmaceutical and fertilizer industry.

One the basis of gear arraignment this gar pump can classified as ,

Internal Gear pumps(reciprocating pumps)

External Gear pumps

Internal Gear pumps

In this types of gear pumps , there are two types of gears and both are of different size. So in internal gear pump gears are always of different size.

External Gear pumps

In external Gear pumps , there are two gears of same sized .This type of pump is used in hydraulic type applications.

Lobe Pumps

Lobe pumps are nothing but rotary types of positive displacement pumps( reciprocating pumps). This is mostly used in pharmaceutical and food industry. This pump is almost same as gear pump. This pumps is suitable for liquid or fluid having high viscosity .

Air Operated Diaphragm Pumps ( AODD pumps)

AODD pump is diaphragm pump which use two number of chambers to transfer the fluid(reciprocating pumps) .This types of positive displacement pumps use air for leafing or transfer of fluid. In AODD pumps there are two number of diaphragms. Pressure and flow of air is key parameter for design of a diaphragm pump.

Piston Pumps

Piston pump is typical type which comes under the types of positive displacement pumps. It also called as plunger pump. This type of pump contain a piston or plunger in a cylindrical body . Stoke of piston transfer a fix volume of liquid or fluid . This pump can give constant or fix volumetric flow by setting its number of stokes .This is one of the type of reciprocating pumps .

Piston pump is suitable for highly viscous fluid , slurry transfer . This pump is suitable for high pressure requirements .One of the main disadvantage of this pump is , “this pump is not suitable for high volumetric floe requirements” . Piston pump can use for very high pressure requirement . Another dis-advantages of piston pump is this pump is its maintenance cost( reciprocating pumps) , this pump required high maintenance so maintenance costing is high .

Advantages of positive displacement pumps

The main advantages of positive displacement types of pumps are ,

Suitable for slurry and high viscosity fluids

We can transfer semi-solid type of fluids using this type of pump.
If pressure requirement is high , this pump is very good in operating point of view.
It gives a constant or fixed volumetric flow as per our requirement

Dis-advantages of positive displacement pumps

the main disadvantages of all types of positive displacement pumps.

This are not suitable for high flow rate type of operating(reciprocating pumps).
Maintenance is difficult as compare to types of centrifugal pumps

this are high pressure pumps , so extra safety is required for safe operation

Application

The main application of this type of pumps is it is used in pharmaceutical industry for transfer of slurry , transfer of filter cake(reciprocating pumps) .In petroleum, petrochemical industry this type of pumps is used for transfer of oil and other crude oil products .

Conclusion

From above article it is clear that there are two types of positive displacement pumps , first is reciprocating pump and second is rotary pump .This article clear that how a positive pump is different as compare to centrifugal pumps. Also get idea about what are the main advantages and dis-advantages of positive displacement types of pumps.

See Also

Unit operation

reciprocating pumps

Frequently asked questions and answers on possitive displacement pump

What is a positive displacement pump?

A positive displacement pump is a type of pump that operates by trapping a specific amount of fluid in a chamber and then forcing it into the discharge pipe, creating a steady flow.

How does a positive displacement pump differ from a centrifugal pump?

Unlike centrifugal pumps, which use centrifugal force to impart velocity to the fluid, positive displacement pumps rely on mechanical action to move fluid by trapping and forcing it through the pump.

What are the advantages of using a positive displacement pump?

Positive displacement pumps offer advantages such as high pressure capabilities, self-priming capabilities, the ability to handle viscous fluids, and consistent flow rates regardless of changes in discharge pressure.

How does a reciprocating pump function?

A reciprocating pump uses a piston or plunger to create a back-and-forth reciprocating motion. As the piston moves, it draws fluid into the chamber during the suction stroke and pushes it out during the discharge stroke.

What are the common applications of reciprocating pumps?

Reciprocating pumps are commonly used in applications that require high-pressure pumping, such as oil and gas production, hydraulic systems, water jetting, and high-pressure cleaning.

What is the working principle of a rotary pump?

Rotary pumps utilize rotating mechanisms, such as gears, lobes, or screws, to trap and move fluid. The rotating motion creates a void that is filled with fluid, which is then carried to the discharge side of the pump.

What are some typical applications of rotary pumps?

Rotary pumps are widely used in applications such as fuel transfer, lubrication systems, chemical processing, pharmaceutical manufacturing, and food processing.

What are the advantages of using rotary pumps?

advantages and disadvantages of positive displacement pumps:

Advantages	Disadvantages
Can handle high-viscosity fluids	Limited to specific flow rates and pressure ranges
Provides a constant flow rate	Requires careful monitoring to prevent damage or leakage
Can generate high discharge pressures	Higher initial cost compared to centrifugal pumps
Suitable for pumping shear-sensitive materials	Requires periodic maintenance and potential downtime
Self-priming capabilities	May not be suitable for large-scale industrial applications
Can handle a wide range of fluid viscosities	Pulsation in flow can occur with certain pump types
Offers reversible flow capabilities	Requires proper lubrication and cooling for certain pumps
Suitable for applications with varying discharge heads	Can be sensitive to changes in fluid properties
Well-suited for metering and dosing applications	May produce more noise compared to centrifugal pumps
Can handle abrasive, corrosive, and slurry fluids	Not as energy-efficient as certain centrifugal pump designs

It’s important to note that the advantages and disadvantages can vary depending on the specific type of positive displacement pump and its application.

Rotary pumps offer benefits such as smooth and continuous flow, ability to handle varying viscosities, reduced pulsation, and lower shear rates, making them suitable for delicate fluids or shear-sensitive materials.

How does a diaphragm pump operate?

Diaphragm pumps use a flexible diaphragm that moves back and forth to create suction and discharge strokes. This movement creates a pressure difference, allowing the fluid to be pumped.

What are the advantages of diaphragm pumps?

Diaphragm pumps are known for their ability to handle corrosive, abrasive, or viscous fluids. They are also self-priming, can run dry without damage, and provide gentle and pulsation-free pumping.

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5.8 Types of positive displacement pumps