PUMP

Centrifugal pump

Pumps are used to convert mechanical energy into hydraulic energy or pressure energy. Pumps have wide application in pumping water, fuel, chemical and viscous fluids like lubricants.

Water pumps are used for residential from bore wells or open wells for residential buildings and agriculture purpose.

Types of Pumps                                   Applications

  1. Reciprocating pumps
  2. Centrifugal pumps To pump water overhead takes in building and also for agriculture.
  3. Compressor Pumps
  4. Submergible pumps
  5. Vane Pumps:- To pump semi-viscous liquids.
  6. Gear Pumps:- To pump viscous oil for lubricants.
  7. Injector Pumps:- To pump boiler feed water during its operation.
  8. Different types of fuel Pumps:- To pump petrol or diesel oil in I.C Engines.
  9. Screw Pumps:-  To pump liquid mixed with solid materials

Also read: Basics of Thermodynamics

Reciprocating Pumps:-

The reciprocating pumps are classified as

Single Acting Reciprocating Pumps:-

Working of Single Acting Reciprocating Pump:-

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It consists of the following parts

  • Cylinder with a piston
  • Piston connecting rod, crank and Crankshaft rod.
  • Suction pipe with a foot valve (one-way valve) & filter.
  • Delivery pipe.
  • Suction valve.
  • Delivery valve.

The crankshaft is coupled to an electric motor or a diesel engine. When the motor or engine is started, the piston moves to and from inside the cylinder. When the piston moves right in the direction of the arrow, a vacuum will be produced in the cylinder due to which the suction valve opens and enters the cylinder through the suction pipe.

When the piston moves in the left direction, the pressure is created in the water due to which the delivery valve is opened and water is forced into the delivery pipe and finally to the required height.

Double Acting Reciprocating Pump:-

Working:-

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In the double-acting pump, water acts on both sides of the piston. There are two suction pipes and two delivery pipes, when there is a suction stroke on one side of the piston, there will be a delivery stroke on the other side of the piston. Thus, for each revolution of the crankshaft, there will be two delivery stroke and so, double the amount of water is delivered, by this type of pump.

Difference between Single-Acting and Double-Acting Pumps:-
Single-ActingDouble-Acting
One suction pipe onlyTwo suction pipes.
One delivery pipe onlyTwo delivery pipes
Water acts on one side of the pistonWater acts on both sides of the piston.
During one rotation of the shaft, there is only one delivery strokeTwo delivery strokes
Water pumped will be lessDouble the amount
Power of the motor pr engine is lessHigher power is required
Cost is lessCost is more.
Centrifugal Pump:-

The main parts of a centrifugal pump are given as follows:-

  • Impellers
  • Casing
  • Suction pipe fitted with a foot valve (one-way valve) and filter, the foot valve will not allow the water to come down.
  • Delivery pipe

Impeller

    The rotating part of the centrifugal pump is called impeller. It consists of backward curved vanes. The impeller is mounted on a shaft which is connected to the shaft of an electric motor.

Casing

The casing of a centrifugal is similar to the casing of a rotation turbine.

It is an air-tight passage surrounding the impeller and is designed in such a way that the kinetic energy of the water discharged at the outlet of the impeller is converted into pressure energy before the water leaves the casing and enters the delivery pipe.

The following three types of casing are commonly adopted:-

  • Volute Casing:-

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    Figure: Volute casing

figure shows the volute casing, which surrounded the impeller. It is of spiral type in which area of gradually. The increase in area of flow decreases the velocity of flow. The decrease in velocity increases the pressure of the water flowing through the casing. It has low efficiency due to the formation of eddies.

  • Vortex Casing:-
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If a circular chamber is introduced between the casing and the impeller as shown in figure, the casing is known as vortex casing. By introducing the circular chamber, the loss of energy due to the formation of eddies is reduced to a considerable extent. Thus the efficiency of the pump is more than the efficiency when only volute casing is provided.

  • Casing with Guide Blades (Diffuser):-

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    Figure: Casing wit guide blades or diffuser

In this casing, the impeller is surrounded by a series of guide blades mounted on a ring which is known as a diffuser. The guide vanes are designed in such a way that the water from the impeller enters the guide vanes without stroke. Also, the area of the guide vanes increases, thus reducing the velocity of flow through guide vanes and consequently increasing the pressure of water. The water from the guide vanes then passes through the surrounding casing which is in most of the cases concentric with the impeller as shown in the figure.

  • Suction pipe with a foot valve and filter:-

A pipe whose one end is connected to the inlet of the pump and another end dips into water in a sump is known as a suction pipe. A foot valve which is a Non-return valve or one-way type of valve is fitted at the lower end of the suction pipe. The foot valve opens only in the upward direction. A filter is also fitted at the lower end of the suction pipe.

  • Delivery pipe:-

A pipe whose one end is connected to the outlet of the pump and other end delivers the water at a required height is known as deliver pipe.

Working of centrifugal pump:-

The centrifugal pump acts as a reverse of an inward radial flow reaction machine. This means that the flow in centrifugal pumps is in the radial outward directions. The centrifugal pump works on the principle of forced vortex flow which means that when a certain mass of liquid is rotated by an external torque, the rise in pressure head of the rotating liquid takes place. The rise in pressure head at any point of the rotating liquid is proportional to the square of tangential velocity of the liquid at that point (that is a rise in pressure head= ϒ2/2g or w2r2/2g). Thus, at the outlet of the impeller, where the radius is more, the rise in pressure head will be more and the liquid will be discharged at the outlet with a high-pressure head. Due to this high pressure head, the liquid can be lifted to a high level.

  • Difference between Reciprocating Pump & Centrifugal Pump:-
Reciprocating pumpCentrifugal pump
Can be used for high headMedium head
Can pump less quantity onlyLarge quantity can be pumped.
Discharge is not continuousContinuous flow
Cost is highCost is low
Can not run at high speed.Can run at high speed
Can not pump viscous fluid.Can pump viscous fluid

 

 

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