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3 Oil Types for Elevators

Three Oil Types for Hydraulic Elevators

www.oilscrubber.com

Michael Johnson

 

Vegetable

What is referred to a vegetable oil or vegie oil is an ester. Vegetable oil is sold as biodegradable, which most people assume means it is environmentally friendly, however this is not the case.  The EPA regulates vegetable oil the same way that it does petroleum oil. They both have the same environmental impact if spilled and are both regulated under 40 CFR 112.

Vegetable oil can cost two to three times as much a petroleum-based oils.

Esters are formed by combining a fatty acid(triglyceride) and an alcohol group in the presence of an acid catalyst; this reaction removes the hydrogen molecule.  The problem is that this reaction is reversable.  When water enters the reservoir of the hydraulic elevator, the process reverses resulting in increases in Total Acid Number and alcohol.

Oxidation of the oil results in polymerization, or the thickening of the oil and is noted by increases in oil viscosity and a sticky film in the machine room.

Preventive measure must be used to prevent water contamination of vegetable oils.  Once the chemical reaction has reversed, the oil has physically changed and cannot be saved.

Offline filtration should be used to keep the oil dry and remove contamination.

Vegetable oil is best utilized in low use applications where water ingress can be controlled and operating temperatures are low.  Extended bypass times and limited reservoir residence times will result in base oil destruction.

Petroleum

The American Petroleum Institute (API) categorizes base oils into five groups; the first three groups are petroleum-based oils.

Group I oils are solvent refined, less than 90 percent saturates, greater than .03 percent sulfur and have a Viscosity Index between 80 and 120.

Group I based hydraulic oils are typically the cheapest, bought in bulk between $5 and $10 per gallon.  Group I oil readily absorb additives making them easy to blend and store without the additives dropping out of suspension.

Group I oils will dissolve water and contaminates resulting in emulsions which change the physical characteristics of the hydraulic oil.  When the oil becomes saturated with contaminants, sludge will form in the reservoir and on the walls of the pipes and casing; this oil can be saved if the contaminants are removed.

NZ or non-zinc fluids are commonly made from Group I base oil.  The extra sulfur in the solvent refined fluids can be utilized for its anti-wear properties.  To prevent an adverse chemical reaction from occurring, NZ should not be mixed with any oil containing zinc.  Air entrainment, cavitation and acid formation are possible if the NZ reacts with zinc.

Group II are formed by, hydrotreating, a more complex process than that used in Group I; this process produces a purer base oil which is more than 90 percent saturates, less than .03 percent sulfur and has a Viscosity Index between 80 and 120.

The purer base oil has a more defined molecular chain and has natural antioxidant properties.  Group II oils resists contaminants which can form varnish on hard surfaces if excessive heating occurs.

Group II hydraulic oils are beginning to appear on the market and do not cost much more than Group I hydraulic fluids.  The MSDS will list ingredients as Distillates (petroleum), hydrotreated paraffinic.

Group III base oils are hydrocracked and can be sold as a synthetic because its molecular structure is so well defined.  Additive retention can be difficult, so fluid should not be stored for long periods of time.

Group III fluids have good antioxidant properties and contaminants will form varnish on hard surfaces at hot spots.

Petroleum based fluids have been the standard for hydraulic elevators for over sixty years; most of the equipment is designed to operate with an ISO grade 32 petroleum-based oil.  Offline filtration is recommended to eliminate contaminates and increase the service life of the hydraulic oil and components.  Sludge and varnish formations can be prevented if the oil is kept clean.

Synthetic

Synthetic fluids are beginning to make inroads into the elevator market.  Most synthetic fluids are petroleum-based fluids but have been formulated to increase the benefits and minimize the negative properties of the fluid.

Compatibility with metals and soft parts such as seals and O-Rings must be considered when converting to a synthetic.  Synthetics come with a premium price but offer different advantages based on the formulation, because the formulas are tailored to meet specific needs.

High VI synthetics may fill a gap in the hydraulic elevator market for machines that overheat due to high usage.  Synthetics can have better thermal and oxidation stability than petroleum-based oils and can be formulated to function with high levels of water.

In environmentally sensitive areas, the synthetic can be formulated to be biodegradable and non-hazardous.

Conclusion

Petroleum based oils are still the standard for the elevator industry and will function well in almost every case if the oil is kept cool, clean and dry.  Hydraulic elevators are not designed with inline filtration, so offline filtration is recommended.

Synthetics are becoming available; at a premium price, but can be tailored to fit specific needs such as overheating issues or environmental concerns.

Due to the likelihood of water contamination in hydraulic elevators, I do not recommend the use of vegetable oils. Vegetable oil should only be used if water content is constantly monitored and overheating is not possible.