In this article, we learn what is pump and the types of pumps.
What is Pump?
The pump is a mechanical device that when connected to a pipeline converts the mechanical energy supplied to it into hydraulic energy and transfers it to the liquid.
Hence, the pump increases the energy of flowing fluid. Almost all the pumps increase the pressure energy of the liquid.
The main difference between a turbine and a pump is that in the case of a turbine flow of fluid takes place from high pressure to low pressure whereas in the case of a pump flow of fluid takes place from low pressure to high pressure.
Types of Pumps
Generally, types of pumps are divided into two major groups:
1, Positive-displacement pumps
2. Rotodynamic pumps (Dynamic pressure pumps)
1. Positive-displacement pumps
In these types of pumps, the fluid is sucked and actually displaced or pushed due to the thrust exerted on it by a moving member (piston) which results in lifting the liquid to the desired height. The commonly used positive-displacement pump is a reciprocating pump.
Reciprocating Pumps
A reciprocating pump is a positive-displacement types of pump in which liquid is displaced by a piston-cylinder arrangement which is driven by crank and connecting rod mechanism.
Reciprocating pump is suitable for small capacities and high heads.
Reciprocating pumps can be classified as follows:
1. Single-acting reciprocating pump
2. Double-acting reciprocating pump
Construction of Reciprocating pump
The figure shows the arrangement of a single-acting reciprocating pump. The various components of the reciprocating pump are as follows:
1. Suction pipe and delivery pipe
2. Piston and cylinder
3. Crank and connecting rod mechanism
4. Sump (Reservoir)
1. Suction pipe and delivery pipe
The suction pipe is connected to the sump of the pump and through this pipe, the liquid is sucked into the pump. The delivery pipe is connected to the discharge end and it carries liquid at high pressure through some height. It also consists of a non-return valve.
2. Piston and cylinder
The piston reciprocates inside the cylinder. The connecting rod transfers the rotary motion of the crank into the reciprocating motion of the piston.
3. Crank and connecting rod mechanism
The crank is mounted on a crankshaft and it is driven by either an I.C. engine or an electric motor. The crank is connected to the piston by connecting the rod hence the rotary motion of the crank is converted into the reciprocating motion of the piston.
4. Sump
It is the reservoir through which the liquid is pumped into the system,
Single Acting Reciprocating Pump
The figure shows the arrangement of single acting reciprocating pump which has the same construction as discussed above.
Initially the crank is at IDC and starts rotating in clockwise direction. When the crank rotates, the piston moves towards right side and on the left side of the piston vacuum is created. This vacuum opens the suction valve and the liquid will be forced from sump to the left side of the piston. When the crank reaches to ODC, the piston is on extreme right side the suction stroke is completed.
At the end of suction stroke, the cylinder is full of liquid. When the crank rotates from ODC to IDC in clockwise direction, the liquid will be compressed and high pressure will be built in the cylinder. Because of high pressure delivery valve opens and liquid is delivered through the delivery pipe.
At the end of delivery stroke, the crank is at IDC and position.
Applications of Reciprocating Pumps
Reciprocating pumps are used in the following applications:
It is used as a feed water pump in boilers, hydraulic jacks, kerosene pumps, hand-operated pumps, etc.
It is used in industries and the agriculture field.
It is also used in service stations for pressure washing.
2. Rotodynamic or dynamic pressure pumps
These pumps have a rotating element (impeller) through which as the liquid passes its angular momentum changes hence the pressure energy of the liquid is increased. These pumps do not push the liquid as in the case of a positive-displacement pump. The commonly used rotodynamic pump is a centrifugal pump.
Centrifugal Pumps
The hydraulic machines which convert mechanical energy into hydraulic energy are called pumps. The hydraulic energy is generally in the form of pressure energy.
If the mechanical energy is converted into pressure by using centrifugal force acting on the fluid, the hydraulic machine is known as centrifugal pump.
It works on the principle of forced vortex flow which means that when a certain mass of liquid is rotated, the rise in pressure of the rotating liquid takes place.
The main parts of a centrifugal pump are as follows:
1. Impeller
2. Casing
3. Suction pipe
4. Delivery pipe
It is a rotating part of a centrifugal pump. It consists of backward-curved vanes. It is mounted on a shaft which is connected to the shaft of an electric motor.
It is an air-tight passage surrounding the impeller. It 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 section. The casing is of spiral type in which the area of flow increases gradually. This increase in the area reduces the velocity of flow and increases the pressure of the liquid flowing through the casing.
It is a pipe whose one end is connected to the inlet of the pump and other end dips into the water sump. A non-return valve is fitted at the lower end of the suction pipe. It opens only in the upward direction, To remove dust, dirt, etc. a strainer (filter) is also fitted at the lower end of the suction pipe.
It is a pipe whose one end is connected to the outlet of the Pump and another end delivers the water at the desired height. To control the flow of liquid a delivery valve is connected to this pipe.
Applications of Centrifugal Pump
It is used in the domestic water supply.
It is used in energy and oil refineries, power plants.
It is used in building services for pressure boosting, fire protection sprinkler systems, air conditioners, etc.
It is used in boiler feed applications, waste water management, irrigation, etc.
It is also used in chemical and process industries.
Comparison between Centrifugal Pump and Reciprocating Pump
Centrifugal Pump
The flow rate is continuous and smooth.
It can supply large quantities of liquid.
These pumps run at high speed.
The working of these pumps is smooth and without much noise.
Cost of centrifugal pump is low.
The cost of maintenance and installation is also low.
Efficiency of these pumps is high.
It requires smaller floor area.
Reciprocating Pump
The flow rate is fluctuating.
It can supply a small quantity of liquid only.
These pumps run at low speed.
The working these pumps is complicated and with much noise.
Cost of reciprocating pump is high.
The cost of maintenance and installation is also high.
Efficiency of these pumps is low.
It requires larger floor area.