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275B SER
800-00152
ELIMINATING AIR FROM THE SYSTEM
ELIMINATING AIR FROM THE SYSTEM
ELIMINATING AIR FROM THE SYSTEM
ELIMINATING AIR FROM THE SYSTEM
ELIMINATING AIR FROM THE SYSTEM
All hydraulic fluid contains some dissolved air, usually about 10% by volume. Under increased pressure, the fluid will
absorb much more air. Aeration in a hydraulic circuit is the presence of free air in places where there ought to be only
fluid. Usually the air will be in the form of bubbles dispersed through the fluid.
Difficulties with aeration will occur more frequently as flow velocities increase in hydraulic components. This
section covers some of the causes of air being introduced into a system and the suggested practices to effectively
reduce and eliminate this problem.
CAUSES
CAUSES
CAUSES
CAUSES
CAUSES
The most common places for air to be introduced into a hydraulic system or for aeration to occur are listed below:
1. Damaged inlet line; loose or defective fittings or seals at any component.
2. Damaged return line; loose or defective fittings or seals at any component.
3. Damaged or worn cylinder rod, packing or seals.
4. Cracked junction blocks, tees or piping.
NOTE:
NOTE:
NOTE:
NOTE:
NOTE: Because fluid acts as a sealant at atmospheric pressure, when system drops below atmospheric pressure air
may be drawn in where fluid will not necessarily leak out.
5. Fluid level too low. This can cause vortexing at pump inlet in reservoir, thus drawing in air.
6. Air trapped in filter with no means of bleed off.
7. Return fluid discharged above fluid level in reservoir. Poor baffling in the reservoir can also cause turbulence and
resultant introduction of air.
8. Air trapped in system during original filling, or when adding fluid for makeup.
DAMAGE TO THE SYSTEM
DAMAGE TO THE SYSTEM
DAMAGE TO THE SYSTEM
DAMAGE TO THE SYSTEM
DAMAGE TO THE SYSTEM
The condition listed in the previous paragraph all contribute to inducing air into a hydraulic system. This aeration can
cause jerky and uneven movement in pumps and motors, seizure, overheating, and possibly eventual failure.
HOW TO AVOID AERATION
HOW TO AVOID AERATION
HOW TO AVOID AERATION
HOW TO AVOID AERATION
HOW TO AVOID AERATION
Regular inspection and regular maintenance are the best ways to prevent air from being introduced into a hydraulic
system. Keeping all connections and fittings tight is the easiest way to avoid the introduction of air.
Return fluid entering the reservoir will create aeration if it is discharged above the main body of the fluid in the tank. To
prevent this condition, maintain sufficient fluid in the tank to keep the return line submerged. The pump intake line
should always be below the fluid surface for the same reason.
Improved service life depends on maintaining proper conditions within the system.
