Water the is the most common chemical contaminate in the hydraulic elevator system.  Hydraulic oil is hygroscopic and capable of absorbing moisture from the machine room.  Water can reduce the life of the oil and the hydraulic components by more than 5X.

The quality of the oil determines how much water the oil can contain before the contamination becomes visible. Just because the oil does not look contaminated, does not mean that the water is not  present and not causing damage to the hydraulic system.

Water occurs in 3 phases; dissolved, emulsion and free.  Dissolved water is not visible in the oil and usually occurs up to 600 ppm; old or degraded oil can contain larger amounts in the dissolved state.  It is our experience that water levels over 100 ppm can alter the performance of the hydraulic elevator.

In one recent case, reducing the water content from  250 ppm to less than 50 ppm reduced the reservoir temperature by 15°F.  Reducing the water content of the oil can shorten the leveling times, resulting in less oil bypass time and a reduction in reservoir temperatures.

Hydraulic elevators are high volume; low pressure systems with undersized reservoirs.  The churning of the oil as it travels in and out of the reservoir can cause air entrainment in the oil.  Water induces air entrainment; the undersized reservoir does not allow adequate residence time in the reservoir for the air to be released from the oil.  The same is true of the heat in the oil.

Aeration or foaming of the oil is an indication of water contamination.  Water induced air entrainment can lead to base oil oxidation through micro-dieseling.

Emulsion is the second phase of water contamination, and the point at which most oil is replaced due to water contamination.  In this phase, the hydraulic oil takes on a cloudy or milky appearance; this occurs when the oil can no longer dissolve additional water.

The cloudy appearance does not indicate the oil is bad; it is just an indication that the oil is contaminated.  If the oil is chemically sound and the water is removed, the oil can usually be returned to service.  Thousands of gallons of good oil is disposed of each year which could be saved through proper cleaning.  We call it, scrubbing.  If the base oil is in good condition, the oil can be saved.

Petroleum based hydraulic oil is very robust and can perform for many years if it is kept cool, clean and dry.  Offline scrubbing with a depth filter can restore the hydraulic oil to like new condition if oxidation has not occurred.  A regular routine of oil analysis and oil scrubbing can increase the life of the hydraulic system and reduce the occurrence of failures of valves, seals and motors.

Free water is the third stage of water contamination and is observed as large water droplets in the oil.  Free water indicates severe water contamination, but can actually be a good sign, indicating the oil has the ability to separate from the water.

Many petroleum based oil samples that have been sent to me have arrived with free water in the bottom of the container.  If the oil has the ability to form free water, it can usually be scrubbed and returned to service.  Oxidized oil, that can no longer demulsify or separate from water would be an indication that the hydraulic oil needs to be replaced. 

A word of caution for vegetable or ester based oil.  Water is the natural enemy of vegetable oils; hydrolysis reverses the chemical process used to make the oil.  Even small amounts of water can degrade the oil and lead to the polymerization or thickening of the vegetable oil when the oil is overheated during oil bypass.

Like oxidation of a petroleum based oil, hydrolysis of the vegetable oil is not revisable.  An increases in viscosity and alcohol content is an indication of the degradation of the vegetable oil.  It is of paramount concern that the vegetable oil be kept dry.  Depending on the amount of degrading in the vegetable oil, scrubbing can remove the oxidation by-products, but the oil cannot be restored if it has been chemically changed.  If vegetable oil is used, water should be actively excluded from the system.

No hydraulic oil is intended to last forever, however, it is not necessary to replace the oil due to contamination.  Additives are sacrificial, and can be effectively restored during top off, if the hydraulic system is clean and free of reactive materials.

The purpose of the additives is to improve or minimize the characteristics of the base oil; regular maintenance of the oil in the hydraulic system will extend the life of the existing additives and protect the base oil from oxidation.  Regular oil analysis and offline scrubbing should be a part of a good maintenance program.

For more information on solutions to oil related failures, please visit our website at www.oilscrubber.com and fill out the contact form under the contact link.