by characteristics, such as viscosity at one or more temperatures, pour point, flash point, and in some cases, by specific brands.

Typical compressor cylinder oils will have the following characteristics:

Flash point, F 350 minimum

Viscosity at 210F 45 min - 90 max

Pour point, F +35 maximum

Neutralization number 0.10 maximum

Conradson carbon residue, % 2.0 maximum

Where cylinder lubrication is separate from frame and bearing lubricants, a modified set of characteristics may be specified. Synthetic oils must conform to the manufacturer's requirements and must be used with care as many synthetic oils may cause swelling and softening of neoprenes and certain rubbers or may not be compatible or separable from water.

Some special considerations for lubricants include the provision of a lubrication oil heater to ensure adequate viscosity during cold weather start-up. High compressor discharge temperatures require lubrication flows and characteristics that still lubricate when subjected to 300F or higher discharge air temperature conditions. Finally, oil injection or oil-flooded compressors need adequate oil flow and characteristics to maintain lubrication of temperatures within the cylinders or screws.

A typical lubrication arrangement is shown in figure 11-18.

Discharge Pulsation

Reciprocating compressor discharge lines are subject to pulsations caused by the compressor-forcing frequency. This sets up a resonant frequency in the discharge piping, and the resulting vibration amplification will cause noise, support damage, and piping damage. There

Figure 11-18. - Typical pressure lubrication system.