The work saved by fitting an air vessel to a single acting reciprocating pump is _______.

Explanation:

Reciprocating Pump:

• A reciprocating pump is a positive displacement pump as sucks and raises the liquid by actually displacing it with a piston or plunger that executes a reciprocating motion in a closely fitted cylinder.
• The amount of liquid pumped is equal to the volume displaced by the piston.
• The reciprocating pump is best suited for relatively small capacities and high heads.

Single-Acting reciprocating pump:

• A single-acting reciprocating pump has one suction pipe and one delivery pipe.
• Initially, the crank is at the inner dead centre and rotates in the clockwise direction. As the crank rotates the piston moves towards the right and a vacuum is created on the left side of the piston. This vacuum causes the suction valve to open and consequently the liquid is forced from the sump to the left side of the piston.
• When the crank is outer dead centre the suction stroke is completed.
• When the crank turns from ODC to IDC, the piston moves inward to the left, and high pressure builds up in the cylinder.

Double-acting reciprocating pump:

• In a double-acting reciprocating pump, suction and delivery strokes occur simultaneously.
• When the crank rotates from IDC in a clockwise direction, a vacuum is created on the left side of the piston and the liquid is sucked in from the sump through valve S1. At the same time, the liquid on the right side of the piston is pressed and high pressure causes the delivery valve D2 to open and the liquid is passed on to the discharge tank. This operation continues till the crank reaches ODC.
• Because of continuous delivery strokes, a double-acting reciprocating pump gives a more uniform discharge.

Air vessels:

• An air vessel is a closed chamber containing compressed air in the upper part and liquid being pumped in the lower part.
• One air vessel is fixed on the suction pipe just near the suction valve and one is fixed on the delivery pipe.

The air vessels are used for the following purposes:

• To get a continuous supply of liquid at a uniform rate.
• To save the power required to drive the pump (By the use of air vessels, the acceleration and friction heads are considerably reduced and the work is also reduced).
• To run the pump at a much higher speed without any danger of separation (By fitting the air vessels as close to the pump as possible, the length of the pipe in which acceleration takes place is reduced due to which acceleration head is reduced, and the pump can run at a high speed without separation).

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​The percentage of work saved in pipe friction by fitting air vessels in the case of a single-acting reciprocating pump is approximately 84.8% and in the case of double-acting, it is approximately 39.2 %.