Sponsored by Dow Corning
Tag Links: Hydraulic Lubrication | Fluid Aeration | Cavitation | Lubricant Health
Air and bubbles, or fluid aeration and cavitation, can cause numerous
problems in a hydraulic and lubrication oil system. Lubrication practitioners should be attentive to abnormal noise, poor component response due
to spongy behavior of aerated fluids and high fluid temperature as signs of poor
Aeration occurs when air contaminates the hydraulic fluid. Symptoms include
foaming of the fluid, erratic actuator movements, and a banging or knocking
noise when it compresses and decompresses as it circulates through the
Because air usually enters the hydraulic system through the pump’s inlet,
ensure that the pump inlet lines are in good conditions and all the clamps and
fittings are tight. Flexible intake hoses can age and become porous, so it is
essential to replace them regularly. Aeration accelerates degradation of the
hydraulic fluid, which in turn can cause overheating and burning of the seals.
Regularly check the condition of the pump shaft seal and, when leaking, replace
Cavitation occurs when the pressure acting in a fluid is below the saturation
pressure of a dissolved gas in the fluid. This causes the absolute pressure in
that part of the circuit to fall below the vapor pressure of the hydraulic
fluid, which results in the formation of vapor cavities within the fluid. When
these cavities encounter a region of higher pressure, they will collapse.
Depending on the load pressure of the hydraulic pump, this can cause broad, high
frequency vibrations, noise, material damage and degradation of the oil leading
to mechanical failure of the system components.
Cavitation commonly occurs at the hydraulic pump, where a clogged inlet
strainer or restricted intake line can cause the fluid to vaporize. Check the
inlet strainer filter on a regular basis that it is not clogged.
Operating a hydraulic system above temperatures of 82°C (180°F) should be
avoided, because it can damage seals and accelerate degradation of the hydraulic
fluid. Hydraulic systems dissipate heat through the fluid reservoir; therefore,
the reservoir fluid level should be monitored and maintained at the correct
level. To prevent damage caused by high temperatures, a fluid temperature alarm
should be installed and all high temperature indications investigated and
By carefully monitoring lubricant health and safeguarding against the
possible causes of aeration and cavitation, costly repairs can be avoided and
lubricant life significantly extended.
Source: Dow Corning
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