Air can occur in a fluid in the dissolved and in the free state. Dissolved air will not pose a problem, free air on the other hand will become a problem when it passes through system components. It can cause pressure changes that compress the air and produce a large amount of heat in small air bubbles. This heat can destroy both additives and the hydraulic liquid itself.

Loss of energy
If the amount of free air reaches a certain level, it will have a negative effect on the productivity of the system. Hydraulic systems rely on the fluid being relatively incompressible, while air changes the volume of the liquid. This is due to the fact that air is up to 20.000 times more compressible than the liquid in which it is dissolved. When air is present, a pump has to put more energy in compressing the air, therefore there is less energy left for operating the system. A system in this state is said to be ‘spongy‘.

Air in both dissolved and free state is a potential source of oxidation, accelerating the corrosion of metal parts. Both produce oxides which promote the formation of particulates or form sludge. Wear and interference increase if oxidation debris is not prevented or removed.


  • Loss of transmitted power
  • Reduced pump output
  • Loss of lubrication
  • Increased operating temperature
  • Reservoir fluid foaming
  • Chemical reactions


  • System leaks
  • Pump aeration
  • Reservoir fluid turbulence


  • System air bleeds
  • Flooded suction pump
  • Proper reservoir design
  • Return line diffusers

The RMF vacuum dehydration units are highly efficient in degassing oil.
Want to know how? Call +31 180 62 13 13 or contact us.