July 22, 2021

What is pump?| definition and types of pump.

What is pump

It is a hydraulic machine which converts mechanical energy into hydraulic energy.

A pump is a machine used to move liquid through a piping system and to rise the pressure of the liquid

A pump is a device that moves fluids or sometimes slurries, by mechanical action. Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift, displacement, and gravity pumps.

Pumps operate by some mechanism (typically reciprocating or rotary), and consume energy to perform mechanical  work by moving the fluid.

Pumps operate via many energy sources including manual operation, electricity, engines, or wind power, come in many sizes, from microscopic for use in medical applications to large industrial pumps.

You have to going deeper to understand what actually is pump and its type, so you get better understand, here you are:

Pumps are divided into 2 major categories: Dynamic and Positive Displacement


1. Classification of Pump

  • Dynamic
  • Positive Displacement
Classification of pump

positive displacement pumps

       A Positive Displacement Pump has an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pumps as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The volume is a constant given each cycle of operation.

The positive displacement pumps can be divided in two main classes

  • Reciprocating
  • Rotary

    The positive displacement principle applies whether the pump is a
  • rotary lobe pump
  • progressing cavity pump
  • rotary gear pump
  • piston pump
  • diaphragm pump
  • screw pump
  • gear pump
  • vane pump
  • regenerative (peripheral) pump
  • peristaltic

A Positive Displacement Pumps is a “constant flow machine“.

A Positive Displacement Pump must never operate against closed valves on the discharge side of the pump – it has no shut-off head like Centrifugal Pumps. A Positive Displacement Pump operating against closed discharge valves continues to produce flow until the pressure in the discharge line is increased until the line bursts or the pump is severely damaged – or both.

relief or safety valve on the discharge side of the Positive Displacement Pump is absolute necessary. The relief valve can be internal or external the pump. An internal valve should in general only be used as a safety precaution. An external relief valve installed in the discharge line with a return line back to the suction line or supply tank is highly recommended.

Reciprocating Pumps

Typical reciprocating pumps are:

  • Plunger pumps
  • Diaphragm pumps

Plunger pumps consists of a cylinder with a reciprocating plunger in it. In the head of the cylinder the suction and discharge valves are mounted. In the suction stroke the plunger retracts and the suction valves opens causing suction of fluid into the cylinder. In the forward stroke the plunger pushes the liquid out the discharge valve.

With only one cylinder the fluid flow varies between maximum flow when the plunger moves through the middle positions, and zero flow when the plunger is in the end positions. A lot of energy is wasted when the fluid is accelerated in the piping system. Vibration and “water hammers” may be a serious problem. In general, the problems are compensated by using two or more cylinders not working in phase with each other.

In a diaphragm pump the plunger pressurizes hydraulic oil which is used to flex a diaphragm in the pumping cylinder. Diaphragm pumps are used to pump hazardous and toxic fluids.

Rotary Pumps

Typical rotary pumps are:

  • gear pumps
  • lobe pumps
  • vane pumps
  • progressive cavity pumps
  • peripheral pumps
  • screw pumps

In a gear pump the liquid is trapped by the opening between the gear teeth of two identical gears and the chasing of the pump on the suction side. On the pressure side the fluid is squeezed out when the teeth of the two gears are rotated against each other.

A lobe pump operates similar to a gear pump, but with two lobes driven by external timing gears. The lobes do not make contact.

A progressive cavity pump consists of a metal rotor rotating within an elastomer-lined or elastic stator. When the rotor turns progressive chambers from suction end to discharge end are formed between the rotor and stator, moving the fluid.

Centrifugal pump

A centrifugal pump converts input power to kinetic energy by accelerating liquid in a revolving device – an impeller.

The most common is the volute pump – where fluid enters the pump through the eye of the impeller which rotates at high speed. The fluid accelerates radially outward from the pump chasing and a vacuum is created at the impellers eye that continuously draws more fluid into the pump.

the energy from the pumps prime mover is transferred to kinetic energy according the Bernoulli Equation. The energy transferred to the liquid corresponds to the velocity at the edge or vane tip of the impeller. The faster the impeller revolves or the bigger the impeller is, the higher will the velocity of the liquid energy transferred to the liquid be. This is described by the Affinity Laws.

Centrifugal Pump: A mechanical device used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow.

● Centrifugal pumps are the most popular pump used and are the chief pump type in the class of kinetic pumps.

 ● Used in various sectors such as: agriculture, power generation plants, municipal, industries, domestic purposes, etc.

 ● Common uses include: air, water, sewage, petroleum, petrochemical pumping.

● Consist of two major parts: 1. impeller (a wheel with vanes) 2. Circular pump

Rotating Impeller


● First centrifugal pump was a mud lifting machine in late 1400” s

by Italian Renaissance engineer Francesco di Giorgio Martini.

● Denis Papin developed the first true centrifugal pump in 1687,

which was one with straight vanes that was used for drainage.

● John Appold, who was a British inventor, developed the first curved vane centrifugal pump in 1851.

● True centrifugal pumps developed in late 1600’s in Europe and made its way to U.S. in early 1800’s.

● Widespread use in last 75 years.

● improved performance and better materials of construction have helped improve efficiencies (93%+ for large pumps and 50%+ for small fractional horsepower units).

Fluid flow through the pump.

Types of centrifugal pump

Centrifugal pump:

axial flow type

single stage

multi stage

closed impeller

open impeller

Fixed pitch

Variable pitch

Mixed/radial flow type

Single suction

Double suction

Single stage

Multi stage



Open impeller

Semi-open impeller

Closed impeller

Peripheral type

Single stage

Multi stage



Special type

Jet (eductor)

Gas lift


Axial flow pump

Axial flow pumps, also called propeller pumps, are centrifugal pumps which move fluid axially through an impeller. They provide high flow rate and low head, but some models can be adjusted to run efficiently at different conditions by changing the impeller pitch.

Axial flow pumps are dynamic pumps, meaning they utilize fluid momentum and velocity to generate pump pressure. Specifically, they are centrifugal pumps, which generate this velocity by using an impeller to apply centrifugal force to the moving liquid.

Axial flow pumps are one of three subtypes of centrifugal pumps, the others being mixed flow and radial flow.

Of these three types, axial flow pumps are characterized by the highest flow rates and lowest discharge pressures. They direct flow in a straight line parallel to the impeller shaft (see image below) rather than radially (perpendicular to the shaft).

The impeller is shaped like a propeller and contains only a few (typically three or four) vanes. The impeller is driven by a motor that is either sealed directly in the pump body or by a drive shaft that enters the pump tube from the side. 

The impeller looks and operates similar to a boat propeller, which is the reason why axial flow pumps are also called propeller pumps.

Axial flow pump impeller design and flow.

Radial flow pump

The biggest subsection of the centrifugal pumps is the radial pump. The handled liquid is exiting the impeller radially. The achieved delivery head is proportional to the impeller diameter.

To realize higher heads, several impellers are put in series (multistage pumps), where guide rings lead the handled medium from radial flow to the axial inlet of the next stage.  

Radial flow pumps are centrifugal pumps in which the fluid is pumped perpendicularly to the pump shaft.

The flow mechanism in a centrifugal pump can generally be described as follows: Through a suction flange the liquid flows through the suction hub into the rotating impeller due to an energy fall. The pump unit absorbs mechanical energy from a drive motor through a shaft. The blades of the impeller which is permanently fixed on the shaft exert a force on the fluid and increase its angular moment.

Pressure and absolute speed increase as a result. Consequently, energy is being transferred to the fluid. The energy which is present in kinetic form as an increased absolute speed is usually converted into additional static pressure energy by a diffuser device. Nowadays volute casings or bladed diffusors normally are being used as diffuser devices. In combination with the impeller the diffuser device represents the so-called hydraulic of the pump.

To maintain the flow there also has to be an energy fall directly behind the pump after the outlet from the discharge flange, analogous to the pump inlet. Losses occurring in the system for example due to friction or leakage flows require an increased power consumption of the pump.

Centrifugal pumps differ in their constructive and functional characteristics due to their pre-determined installation location and the liquid to be pumped. For pumps of one model range various installation types may be implemented. The hydraulic characteristics and the pumping performance remain nearly unchanged.

Main characteristics are the design of the shaft in the horizontal or vertical position, the position of the pump connections and the connection type of the pump to the drive unit using a coupling or direct assembly on the motor shaft (block design).

Cross section of pump
Parts of pump

Mixed flow type

A type of pump that mixes features of radial flow and axial flow pumps.

Radial flow pumps are in-line centrifugal pumps that operate on a horizontal plane in relation to the flow direction of the water. Axial flow pumps are the opposite—they are in-line pumps that work on a vertical plane in relation to the water.

Mixed flow pumps are a cross between the two. The impeller sits within the pipe and turns, but the turning mechanism is essentially diagonal, using centrifugal force to move the water along while accelerating it further with the push from the axial direction of the impeller. This creates enough force to generate high rates of flow.

Mixed flow pumps are primarily used in applications requiring a high level of flow combined with relatively low discharge pressure. There are a number of industrial applications where this type of pump can be useful. They are also used to help propel watercrafts, such as jet skis.

Other related Pump Types include: vertical pumps, water pumps, waste water pumps, circulating pumps.

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