ANS:B - making the friction in pipe uniform.

An air vessel provided in a reciprocating pump is for decreasing the acceleration head. Here’s an explanation:

1. Acceleration Head: In reciprocating pumps, the fluid undergoes acceleration and deceleration during each stroke of the piston. This results in fluctuations in velocity and pressure within the pump and the connected piping system.
2. Function of an Air Vessel: An air vessel, also known as an air chamber or surge tank, is typically installed on the discharge side of reciprocating pumps. Its main function is to reduce the pulsations and pressure fluctuations caused by the reciprocating action of the pump.
3. Working Principle: When the reciprocating pump operates, it delivers liquid intermittently due to the cyclic motion of the piston. This creates pressure surges in the discharge line. The air vessel acts as a cushion or buffer by providing a volume of compressible air or gas. As the pump delivers fluid into the vessel during its discharge stroke, the air in the vessel compresses, absorbing excess pressure. During the suction stroke, the compressed air expands, helping to maintain a more uniform pressure and flow rate downstream.
4. Effects: By reducing pressure fluctuations, the air vessel helps in:
   • Reducing water hammer effects (sudden pressure spikes) in the piping system.
   • Minimizing vibrations and stresses on the pump and pipeline components.
   • Providing a more steady flow of liquid downstream from the pump.