Synthetics range in composition types, which includes hydrocarbon based, polyglycols, organic and phosphate esters, and other materials. The common trait is that the molecules that comprise the base lubricant are chemically synthesized for targeted properties and a controlled molecular composition. For example, fire resistance requirements in aviation hydraulic systems will favor phosphate ester fluids. Lack of solubility of hydrocarbon fluids and gases in polyalkyleneglycol fluids prevents thinning of the lubricant in natural gas applications. For our short discussion here, the focus will be on synthetic hydrocarbon based fluids.
Before deciding to use a synthetic lubricant it should be determined if the performance improvement out weighs the higher cost. Factors to consider can involve the following:
- Severe cold temperatures
- Severe hot temperatures
- Extremes going from hot to cold during the duty cycle
Extended drain interval due to:
- Access and convenience
- Shutdown cost
Improved power consumption due to enhanced fluid film and lubricity
Excessive exposure to air/oxygen combined with high heat
As previously indicated, synthetic lubricants may not provide additional cost benefits over modern conventional lubricants in systems which are not operating under extreme or special service requirements, or have continuous exposure to contaminants.
David Doyle, CLS, OMA I, OMA II