PUMPS

Device used to move gases, liquids or slurries.

Moves liquids or gases from lower pressure to higher pressure.

A gas pump is generally called a compressor. In very low pressure-rise applications, the operative equipment consists of fans or blowers.

Machines which convert the mechanical energy into pressure energy

Types of Pumps

Rotodynamic pumps

Positive displacement pumps

Rotodynamic pumps (Centrifugal Pumps)

Produce a head and a flow by increasing the velocity of the liquid through the machine with the help of a rotating vane impeller.

Radial, axial and mixed flow units.

Positive displacement pump

Operates by alternating of filling a cavity and then displacing a given volume of liquid.

Causes a fluid to move by trapping a fixed amount of it then forcing (displacing) that trapped volume into the discharge pipe.

Delivers a constant volume of liquid for each cycle against varying discharge pressure or head.

Classified as:

Reciprocating pumps - piston, plunger and diaphragm

Rotary pumps - gear, lobe, screw, vane.

CENTRIFUGAL PUMPS

Uses a rotating impeller to increase the velocity of a fluid.

When a certain mass of liquid is rotated by an external torque, the rise in pressure head of the rotation 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.

Works by the conversion of the rotational kinetic energy, typically from an electric motor or turbine, to an increased static fluid pressure.

The rotation of the pump impeller imparts kinetic energy to the fluid as it is drawn in from the impeller eye (centre) and is forced outward through the impeller vanes to the periphery.

As the fluid exits the impeller, the fluid kinetic energy (velocity) is then converted to (static) pressure due to the change in area the fluid experiences in the volute section.

Typically the volute shape of the pump casing (increasing in volume), or the diffuser vanes (which serve to slow the fluid, converting to kinetic energy in to flow work) are responsible for the energy conversion.

The energy conversion results in an increased pressure on the downstream side of the pump, causing flow.

Used for large discharge through smaller heads.

Main parts of a centrifugal pump1. Impeller

2. Casing

3. Suction pipe with a foot valve and a strainer

4. Delivery pipe

1. Impeller

Rotating part of a centrifugal pump

Consists of a series of backward curved vanes.

Impeller is mounted on a shaft, which is

connected to the shaft of an electric motor.

2. Casing

An air - tight passage surrounding the impeller

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.

Types of the casings

a) Volute casing b) Vortex casing

c) Casing with guide blades

a) Volute casing

Spiral type in which area of flow increases 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.

A large amount of energy is lost due to the formation of eddies in this type of casing.

b) Vortex casing

Circular chamber is introduced between the casing and the impeller.

The loss of energy due to the formation of eddies is reduced to considerable extent by introducing the circular chamber. The efficiency of the pump is more

c) Casing with guide blades

Impeller is surrounded by series of guide blades

mounted on a ring, which is known as diffuser.

The guide vane are designed in which a way that the water

from the impeller enters the guide vane without stock.

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

3. Suction pipe with a foot - valve and a strainer

A pipe whose one end is connected to the inlet of the pump and other end dips into water in a sump.

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. 4. 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.

Working principle of multistage Centrifugal pump

Consists of two or more impellers

The impellers may be mounted on the same shaft or on different shafts.

Two important function:

a) To produce a high head - the impellers are connected in series (or on the same shaft)

b) To discharge a large quantity of liquid - the impellers (or pumps) are connected in parallel.

Multistage Centrifugal pumps for high head

A number of impellers are mounted in series

or on the same shaft.

The water from suction pipe enters the 1st impeller

at inlet and is discharged at outlet with increased

pressure and taken to the inlet of the 2nd impeller.

If more impellers are mounted on the same shaft,

the pressure at the outlet will be increased further.

Multistage Centrifugal pumps for high discharge

The pumps should be connected in parallel.

Each of the pumps lifts the water from a

common pump and discharges water to a

common pipe to which the delivery pipes

of each pump is connected.

Each of the pump is working against the

same head.

RECIPROCATING PUMP

Reciprocating-type pumps use a piston and cylinder arrangement with suction and discharge valves integrated into the pump.

Mechanical energy is converted into hydraulic energy (or pressure energy) by sucking the liquid into a cylinder in which a piston is reciprocating (moving backwards and forwards), which exerts the thrust on the liquid and increases its hydraulic energy (pressure energy).

The pumps can be powered by air, steam or through a belt drive from an engine or motor.

Used for pumping highly viscous fluids including concrete and heavy oils.

Classification of reciprocation pumps

1. According to the water being in contact with one side or both sides of the piston.

i) Single - acting pump ii) Double - acting pump.

2. According to the number of cylinders provided.

i) Single cylinder pump ii) Double cylinder pump iii) Triple cylinder pump.

Working principle of a reciprocating pump

1. A cylinder with a piston, piston rod,

connecting rod and a crank.

2. Suction pipe

3. Delivery pipe

4. Suction valve

5. Delivery valve

Working principles of double acting reciprocation pump

Slip of reciprocating pump

Difference between the theoretical discharge and actual discharge of the pump.

AIR VESSELS

Closed chamber containing compressed air in the top portion and liquid (or water) at the bottom of the chamber.

Act like an intermediate reservoir.

i) To obtain a continuous supply of liquid at a uniform rate.

ii) To run the pump at a high speed without separation.

Cavitation in pumps

Phenomenon of formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure and the sudden collapsing of these vapour bubbles in a region of higher pressure.

When the vapour bubbles collapse, a very high pressure is created.

The metallic surface, above which the liquid is flowing, is subjected to this high pressure, which causes pitting acting on the surface.

Cavities are formed on the metallic surface and also considerable noise and vibrations are produced.

Priming

ROTARY PUMPS

Rotary pumps are the positive displacement type pumps having circular motion, and are without valves and can deliver a constant capacity against variable pressure. Pumping oils or other liquids having some lubricating qualities.

Working principles of Gear and Vane pumps

EMBED Equation.DSMT4

EMBED Equation.DSMT4

GEAR PUMP (External)

GEAR PUMP (Internal)

VANE PUMP

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