Mechanical Construction

The cylinder is generally constructed of cast iron and includes the water jacket. The bore is machined and brought to a good finish to reduce the vane sliding friction. The inlet and outlet connections are flanged. The heads, which also house the bearings and stuffing box, are also made of cast iron.

The rotor and shaft extension are machined from a single piece of bar stock or from a forging in all but the largest sizes, where the rotor and shaft may be made as two separate parts. The material is carbon steel for the single-piece models. The larger compressors, using the two-piece rotor arrangement, use carbon steel for the shaft and cast iron for the rotor body. The rotor body is attached to the shaft using a press fit. Keys are used to lock the rotor body to the shaft. Vanes attach to the rotor body by means of milled slots.

For the lubricated machines, vanes are made of a laminated material impregnated with phenolic resin. For a non-lubricated design, carbon is used. The vane number influences the differential pressure between adjacent vane cells. This influence becomes less as the number of vanes increases.

Rolling element bearings are widely used, generally the roller type. Seals are either a packing or mechanical contact type. Packing and bearings are lubricated by a pressurized system. For the non-flooded, lubricated compressor a multiplunger pump, similar to the one used with reciprocating compressors, is used. Lubrication is directed from the lubricator to drilled passages in the compressor cylinder and heads. One teed is directed to each of the bearings. Other feeds meter lubrication onto the cylinder wall. As the vanes pass the oil injection openings, lubricant is spread around the cylinder walls to lubricate the vane tips and eventually the vanes themselves. The oil entering the gas stream is separated in the discharge line. Because of the high local heat, the lubricant may have broken down and, therefore, is not suitable for recycling.

Flooded compressors pressure feed a large amount of lubricant into the compressor where it both cools the gas and lubricates the compressor. It is separated from the gas at the discharge line and recycled.

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