Short Answer:
Air vessels in hydraulic machinery are closed chambers fitted near reciprocating pumps to smoothen the flow of liquid and reduce energy losses. They contain compressed air and help absorb the pressure variations created during the suction and delivery strokes.
Their main role is to minimize pulsations, maintain a nearly uniform discharge, reduce frictional losses in pipes, and prevent water hammer effects. Air vessels are especially important in reciprocating pump systems where flow is not continuous.
Detailed Explanation:
Role of air vessels in hydraulic machinery
In hydraulic machinery, especially reciprocating pumps, the flow of fluid is not smooth or continuous. This is because these pumps operate by back-and-forth motion (reciprocation), which leads to periodic suction and discharge. This causes flow pulsations, resulting in energy losses, vibrations, noise, and increased wear and tear on the system.
An air vessel is a closed container, usually cylindrical, fitted on the suction and delivery side of a pump. The top part of the vessel contains compressed air, while the lower part contains liquid. As the pump works, the liquid level in the vessel moves up and down, compressing and decompressing the air. This action absorbs the pulsations and stores energy temporarily, which is then released smoothly.
Functions of Air Vessels
- Smooth flow of fluid
In reciprocating pumps, the discharge is not steady due to the piston’s back-and-forth movement. The air vessel absorbs the excess pressure during the delivery stroke and releases fluid during the suction stroke, making the flow nearly continuous. - Reduces friction losses
Continuous flow reduces the formation of turbulence in pipelines. This results in lower frictional head losses, improving the efficiency of the pump system. - Minimizes acceleration head
Without an air vessel, the liquid in the pipe has to speed up and slow down with each stroke, creating an acceleration head. This causes extra energy loss. Air vessels greatly reduce this effect by buffering flow variations. - Controls water hammer
Sudden changes in flow rate or valve closures can cause pressure surges (water hammer). Air vessels help absorb these shocks, reducing the risk of damage to pipes and pump components. - Improves pump performance and life
By reducing vibrations and pressure fluctuations, air vessels protect the pump and other hydraulic components from stress and fatigue, leading to longer operational life and lower maintenance.
Application in Hydraulic Systems
Air vessels are widely used in:
- Reciprocating pumps (especially double-acting types)
- Boiler feed pumps
- Industrial water supply systems
- Oil pipelines
- Irrigation pumping systems
In all these systems, they help balance flow, save energy, and reduce mechanical strain.
Conclusion:
Air vessels play a vital role in hydraulic machinery by ensuring smooth fluid flow, reducing energy losses, and protecting system components. They are essential in systems with pulsating discharge like reciprocating pumps, where they absorb pressure fluctuations and deliver a uniform output. This improves efficiency, safety, and longevity of the entire hydraulic system.