Reciprocating compressors seals

The only other variables that affect performance are the inlet-discharge valves, which control flow into and out of each cylinder. Although reciprocating compressors can use a variety of valve designs, it is crucial that the valves perform reliably. If they are damaged and fail to operate at the proper time or do not seal properly, overall compressor performance will be substantially reduced. 

In oxidizing, oil becomes thicker and it deposits carbon and gummy, resinous substances. These accumulate in the piston-ring grooves of reciprocating compressors and in the slots of vane-type units, and as a result, they restrict free movement of components and allow air leakage to develop. The deposits also settle in and around the valves of piston-type compressors, and prevent proper sealing. 

Figure 7.18. Heavy-duty centrifugal, axial, and reciprocating compressors, (a) Section of a three-stage compressor provided with steam-sealed packing boxes (DeLaval Steam Turbine Co.), (b) An axial compressor (Clark Brothers Co.), (c) Double-acting, two-stage reciprocating compressor with water-cooled jacket and intercooler (Ingersoll-Rand Co.).

Cleanliness of the gas is important. Lubricant oil must be kept out of the process stream for a variety of reasons. The air used on the compressor seals (see below) must be free of oil and particulate matter. The presence of fine particles in the gas is not as damaging in the short term as it would be in a reciprocating machine. Some users have in fact removed suction screens, preferring to deal with the occasional fine particle than with the large debris associated with a screen failure [35]. Even in the absence of solids contamination, there is a buildup on the impellers. The source is organic materials present in the cell gas. These may come from the brine or from reaction of cell components with the gas. The amount of material formed was greatly reduced by the adoption of metal anode technology. Accumulation of solids on the impellers is not a frequent cause of compressor shutdown, but removal of deposits still should be part of the routine overhaul procedure. 

Three types of piston seals are used in reciprocating compressors... 

The major difficulty with these reactors is in the outside recycle pump, especially at high temperatures. Reciprocating pumps require seal rings, and these cannot take the high temperature needed for most reactions. If the recycle gas is cooled down before entering the compressor, it must be reheated before it enters the reactor again. This makes them complicated in construction and excessive in cost. 

If a gas leak test is called for, the test can take place shortly after the hydrotest, especially on the reciprocator cylinder or centrifugal or rotary compressors, where the gas is tested without end seals. 

It is especially difficult to seal pistons with reciprocating motion. Piston rings are suitable as piston seals in piston compressors up to 1500 bar. Above 200 bar, lubrication is generally required. 

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