A pump is a mechanical device or hydraulic machine that converts mechanical energy to hydraulic energy. The pump gives pressure energy to the fluid at its outlet.
A reciprocating pump is a special type of pump in which the reciprocating motion of a piston is used to pump water to the required area.
Reciprocating pumps are mainly used where the delivery pressure of the fluid is very large.
Reciprocating Pump was invented by a greek inventor Ctesibius in 200 BC.
Reciprocating pumps come in the category of positive displacement machines.
A reciprocating pump is suited where a small discharge and a high head are required.
In reciprocating pumps, reciprocating motion is used to increase the pressure energy of the fluid. So it is named as reciprocating pump.
A reciprocating pump is a special purpose pump. This pump is used not commonly like a centrifugal pump. It is used in only special cases like in car washing center where very high pressure of water is required to wash cars.
Using the reciprocating pump we can get very high fluid pressure at the outlet nearly 10 – 20 Bars whereas in the centrifugal pump we can get only 2 – 5 Bars of pressure.
The reciprocating pump is mainly used where you need an accurate flow rate.
In this pump, the flow rate is controlled by controlling the speed of the movement of the piston. For a low flow rate, the piston will move slowly and for a high flow rate, the piston will move in fast motion.
Using a reciprocating pump, we can get very precise flow rate with an inaccuracy of plus-minus one (+-1). Let’s say we need to have a flow rate of 40 litre/min, then using the reciprocating pump we can have a very precise flow rate which can vary from 39 liters/min to 41 liters/min. As it can give a precise flow rate so it is known as a dosing pump.
Parts Of Reciprocating Pump:
This cylinder contains a piston. The cylinder store the water before delivery to the required area. It is also used to create a vacuum for the suction of fluid.
The piston is present inside the cylinder. This piston moves backward and forward. This piston is used to create a vacuum and exert thrust on the fluid.
3 Piston Rod:
A rod is connected to the piston and is known as piston rod. This piston rod is further connected to the connecting rod.
4 Connecting Rod:
The connecting rod is connected to the piston rod on one end and crank on the other end.
The rotational motion of the crank provides the reciprocating motion to the piston.
4 Suction Valve:
When the piston goes forward and backward repeatedly, the suction valve present in the front side of the piston gets on and off simultaneously with the piston. A suction valve is placed in the suction pipe.
5 Suction Pipe:
It is the pipe in which the suction happens. The water from the sump or reservoir is sucked through this pump and this pipe delivers water to the cylinder.
6 Delivery Valve:
The delivery valve is fit in the delivery pipe. This is a non-return valve. This valve opens when the fluid is needed to be delivered in the required area.
7 Delivery Pipe:
The delivery pipe is used to deliver the water from the cylinder to the desired area where the water is needed to be delivered.
8 Reservoir or Sump:
The reservoir is present in the bottom and is used to store the fluid which is to be pumped using a reciprocating pump.
Working Of Reciprocating Pump:
- When the piston goes continuously in forward and backward direction then the suction valve present in the suction valve and delivery valve opens and closes simultaneously with the movement of the piston.
- The distance from the surface of the fluid to the centre of the piston where the piston rod is connected is called the suction headAdvertisementand the distance from the center of the piston to the outlet of the delivery pipe is called the delivery head.
- The connecting rod is connected to a crank. The crank has a radius in which it rotates. The crank is connected to a motor. As the motor rotates the crank also rotates.
- The crank rotates in a clockwise direction. When the crank rotates in the top semi-circle i.e from P to Q, the piston moves backward and when the crank moves in the bottom semi-circle i.e. from Q to P, the piston moves forward.
- The piston moves according to the angle made by the crank. At point P ( θ=0 ) to Q ( θ=180 ).
- At starting, the piston is at point P ( θ=0 ), when the tip of the crank reaches the rightmost point Q ( θ=180 ) the piston also moves to the rightmost point, and vacuum is created in the cylinder.
- The atmospheric pressure acts on the surface of the fluid and also there is atmospheric pressure on the suction pipe. The suction valve present on top of the suction pipe can open only in the top direction.
- As there is vacuum in the cylinder and atmospheric pressure in the suction pipe, the suction valve will open due to pressure difference and as the suction valves open a partial vacuum is created in the suction pipe.
- As there is a partial vacuum in the suction pipe and atmospheric pressure acts on the surface of the fluid so the fluid travels from the high-pressure region to the low-pressure region and will enter the suction pipe and in this way the whole cylinder is filled with the fluid.
- When the cylinder is completely filled with water the suction valve closes.
- After that, the crank moves from the rightmost position towards the bottom-most position ( θ=180 to θ=270 ). As the crank move towards the bottom-most position the piston moves forward and pressure in the fluid present inside the cylinder increases and when the pressure in the cylinder exceeds the atmospheric pressure, the delivery vavle is opened and the fluid flows upward at high pressure and flows out to the required area from the outlet of the delivery pipe.
Mathematical Analysis Of Reciprocating Pump:
Some symbols used below,
D= Diameter of cylinder
A = Cross section area of piston or cylinder = π/4 D²
r = Radius of crank.
N = Speed of crank (rpm).
L= Length of stroke = 2r
Amount of liquid Pumped in revolution = Volume Displaced by Piston in one revolution = A x L
Amount of liquid pumped in one sec = A x L x N/60 = ALN / 60
Weight of water lifted per second ( W/s ) =mg = ρQg
W/s = ρgALN / 60
Work done per second by pump ( WD/s )
= Weight of water lifted per second x Total height up to which water is lifted ( Suction Height + Delivery height)
= ρgALN / 60 x ( hs + hd )
Power of pump = WD/s (in 1000 kW).
Advantages of Reciprocating Pump:
1) Reciprocating pump can deliver the required flow rate very precisely.
2) It gives a continuous rate of discharge.
3) It can deliver fluid at very high pressure.
4) No priming is needed in the reciprocating pump.
5) Efficiency of a reciprocating pump is 10% to 20% greater than the efficiency of a Centrifugal Pump.
Disadvantages of Reciprocating Pump:
1) The pump is very costly (Capital cost is high).
2) Viscous liquids are difficult to pump using a reciprocating pump.
3) The maintenance cost of the pump is very high as there is a large number of parts.
4) The flow rate is less.
Applications of Reciprocating Pump:
1) It is used in vehicle washing centers.
2) It is used in small hand-operated pumps such as cycle pumps, football pumps, etc.
3) It is used as an important part of the hydraulic jack.
4 )It is commonly used in gas industries.
5) It is also used in oil refineries.
6) Used in petroleum industries.
7) It is also used in the pneumatic pressure system.