Air Compressor applications are considered demanding especially for wet-type compressors, wherein oil is injected into the compression chamber.
The Air Compressor Oil is required to perform the following functions,
1.) For Reciprocating Types
a. Lubricate (reduce friction and wear) the bearings on the crankshaft,
b. Lubricate the contact between the piston and the cylinder wall, and,
c. Absorb heat in the compression chamber
2.) For Rotary (Screw) Types
a. Lubricate the gears and bearing driving the rotors, and,
b. Absorb heat in the compression chamber
In addition, the Air Compressor Oils should possess the following properties,
a. The right viscosity, as specified by the OEM,
b. Oxidation & carbonization resistance, and stability which is a requirement for long oil-life,
c. Extreme Pressure and Anti-wear capabilities to protect the mechanical components,
d. Outstanding demulsibility behavior, in order to separate the moisture that is bound to get mixed in with the oil, and,
e. Low volatility to reduce oil consumption
Of great importance is oxidation stability or oil-life, as frequent change-oils are a hindrance to plant productivity. Considering that the temperatures in compression chambers reach up < 100oC, and that mineral-based oils oxidize rapidly at 90oC, synthetic-based lubricant have found favor in industry. Most Air Compressor manufacturers promote synthetic lubricants also for the same reason, recommending oil-change intervals for as long as 6,000 – 8,000 working hours.
In addition, synthetics provide higher viscosity index, lubricating excellently despite high temperature conditions, as well being less volatile than mineral-based oils. Poly-alpha-olefins (PAO), esters, and poly-glycols are some of the common synthetic materials utilized, and in selecting the base-oil, a consultation with the OEM is suggested.