An Easy Way to Remove Water From Hydraulic Oil

HeadSpaceFlush-WaterEd Bailey, Bison Steel Inc., got and read The Hydraulic Maintenance Handbook and used the know-how within to deal with water contamination in a hydraulic shear. The oil capacity of the hydraulic tank was 300 gallons (1136 litres).

Initially the oil was circulated through water removal filters. Six filters were used but this only took out some of the water. A variation of the head space flush described in The Hydraulic Maintenance Handbook was then deployed.

The blower side of a shop vacuum was attached to the breather penetration in the tank lid. Air was blown into the head space and exhausted through a 1/2″ diameter hole at the other end of the tank’s head space.

The vacuum was run continuously, 24/7, for 12 days. During the day the shear was operated, which warmed up and circulated the oil in the hydraulic tank. The ambient air was about 30ºF (-1ºC) and the humidity was low.

The pictures below show oil samples taken at different stages of the process.

Oil samples taken at different stages of the water removal process.

From left to right:
1. Original contamination
2. After 6 filters.
3. After 60 hours of head space flush.
4. After 160 hours of head space flush.
5. After 260 hours of head space flush.

As you can see from the pictures, the water was essentially removed after about 160 hours of flushing the head space, and was only slightly better in appearance after 260 hours of flushing.

Sure, blowing unfiltered air through the reservoir head space is not ideal. But any resulting increase in load on the system’s particulate filters can be largely forgiven, because the process removed the water.

Based on an oil cost of (only!) $8/gallon, Ed’s modest investment in The Hydraulic Maintenance Handbook enabled him to save his employer $2,400.00 on this one maintenance problem alone. And that’s a bargain however you do the math.

11 thoughts on “An Easy Way to Remove Water From Hydraulic Oil

  1. Seeing is believing…! Nice job, great idea Ed, thanks for sharing!
    I’m sure there would be other devices (besides a shop vac) that could do the same, but getting the CFM of air is probably as important as the added temperature.

    • Gregg, correct there is more than one way to flush the head space. Obviously, the air must be significantly dryer than the oil. The flow rate has be meaningful but certainly not gale force.

    • There are other ways this can be done. For example, pulling air in through a desiccant breather using a 24VDC vacuum pump.

  2. Brendon,
    Thank You for the info. However this brings up another Question. How much damage does water in hydraulic oil actually do ? I have always been afraid of running water contaminated Hydraulic oil for any extended period.
    160 hours means running this contaminated oil for a month. Would the potential damages to the system not be more than the $2400 saved in not replacing the fluid ?
    Maybe water in hydraulic oil is not a bad a problem as I had thought it was.

    Thank You Again, I always enjoy your articles and look forward to seeing them.

    • Jimmy, your concern is valid enough. But note in this case the shop vac was running 24/7, so 1 week of head space flush; therefore 1 week of daytime operation of the machine. Could there be some collateral damage? It’s always possible. And it depends on the concentration of water in the oil and the type (design) of components in the system.

  3. Hi!
    May I say some comments…
    If vacuum cleaner works should work also more “civilized” method of blowing filtered compressed air that has passed dryer. It is usually available in all more or less proffessional workshops. Using eg some 6 mm air tube + air filter regulator. I am afraid, that any industrial vacuum cleaner that has been in use for a while has “some” leakage of dust…
    I am not sure about possible rate of evaporation of water from oil surface, but I guess the amount of compressed air used to keep air inside tank dry is not sooo big. Cost of air drier is comparable with good industrial vac.

    • David, you are correct. There is more than one way to achieve this. The way described here could be classified as a “hack”. But effective all the same.

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