How does aeration in a hydraulic pump manifest audibly, and what does it indicate?

Aeration in a hydraulic pump, which is the presence of air bubbles within the hydraulic fluid, manifests audibly as a distinct knocking, rattling, or hissing sound emanating from the pump. This unusual noise is often described as sounding like gravel or small stones being pumped through the system. The sound is caused by the implosion, or rapid collapse, of air bubbles as they pass from a low-pressure area to a high-pressure area within the pump. This implosion creates localized shock waves, generating noise and potentially causing erosion damage to internal pump components over time. Aeration indicates that air is being introduced into the hydraulic system, typically due to leaks on the suction side of the pump, a low fluid level in the reservoir allowing the pump to draw in air, or a faulty pump shaft seal. Because hydraulic fluid is virtually incompressible, while air is highly compressible, the presence of air significantly reduces the system's efficiency and responsiveness. The air compresses under pressure, resulting in spongy or erratic cylinder movement and reduced power output. If left unaddressed, aeration can lead to accelerated pump wear, valve malfunctions, and overall system failure. Finding and eliminating the source of air entry is essential to maintain hydraulic system performance and longevity.