Appendix B

Oils and Fluids

A number of synthetic oils and fluids are available for use with high-speed compressor pumps and are recommended for use in single-stage and multi-stage rotary screw, vane, and reciprocating compressor crankcases and cylinders, vacuum pumps, and other compressor applications. Most of these are available in five viscosity grades. These synthetic oils have a number of additives that make them capable of inhibiting carbon build-up and that make them suitable for operating equipment at higher temperatures. Most are formulated to keep water from mixing with the oil and deteriorating its lubricating ability. Manufacturers also claim it is easier for water removal with no need for specialized water-removal processes.

For example, the synthetic compressor oil is formulated with synthetic ester technology that produces a longer life fluid that effectively prevents wear, oxidation, foam, and rust, while its inherent lubricity and thermal conductivity act to reduce heat and energy consumption. This increases the operating efficiency and reduces maintenance costs.

Performance features are maintained across the spectrum with a wide operating temperature range. It has a low pour-point, highviscosity index and the lack of paraffin (wax) makes synthetic oils an excellent all-weather lubricant.

Hydraulic oils are formulated for long life. They typically reduce maintenance costs. This is done by extending drain intervals. AMSOIL’s synthetic AW series of anti-wear hydraulic oils, for example, are recommended for high- and low-pressure gear, vane, and piston stationary and mobile hydraulic systems. They are available in many viscosity grades. The equipment manufacturer usually recommends the viscosity for the device. The oil will operate efficiently in temperatures of -20°F or lower. These oils are shear-stable, long-life lubricants based on high-quality synthetic oil technology. These oils are formulated with an additive system that inhibits oxidation and prevents acid and viscosity increase, inhibits rust, and inhibits foam formation, as well as preventing spongy hydraulics.

There is also thermally stable biodegradable hydraulic oil that is designed to biodegrade to its natural state when subjected to sunlight, water, and microbial activity. It has a very low toxicity level because the oil is formulated with ashless additives that do not contain heavy metals.

Traditional oil-lubricated pumps use oil for lubricating, cooling, and sealing. Oil reduces the friction of pistons or vanes that must slide against the cylinder walls. Older-style rotary vane pumps used drip oilers. The oil merely reduced friction, but newer oil-flooded designs use copious amounts of oil and actually cause the vanes to hydroplane. This not only reduces the friction, but since the vanes do not actually touch the cylinder wall, the vane life is greatly extended. It is common to obtain 30,000 to 40,000 hours of vane life.

Oil removes the heat of friction. When oil returns to the oil sump (or reservoir), the heat is radiated away from the pump. A fan usually blows across cooling fins on the housing. This exchange of heat is important. If oil runs too hot, it carbonizes. Carbonization can cause the pump to overheat and eventually cause its failure.

The amount of oil being fed to the pump affects sealing. Drip-type oilers on rotary vane pumps need sufficient oil to seal the clearances around the vanes. Oil is used primarily for lubrication. The oil seal has a significant internal leakage of air to the pump. This limits the vacuum level the pump can produce. A typical rotary-vane pump of this type can generally produce a maximum vacuum level of about 26 to 27 inches of mercury. The more recent oil-flooded rotary-vane designs use a greater quantity of oil (sometimes as much as 2 gallons per minute) to seal these clearances. This increases the efficiency of the pump and allows maximum vacuum levels of as much as 29.83 inches of mercury. The maximum vacuum achievable at sea level is 29.92 inches of mercury. Rotary-screw pumps are oil-flooded so they can achieve higher vacuum levels with 29.7 inches of mercury being typical. In addition to cooling, oil is used to keep the rotors from touching each other. Most rotary-screw pumps do not use timing gears to drive the rotors. To prevent contact, one rotor drives the other.