Valves are highly stressed wearing parts that account for the majority of compressor downtime. Reciprocating compressors represent 1% of the machinery in Company Refineries but account for 12% of the maintenance budget. The Company spends approximately five million dollars per year for maintenance of reciprocating compressors. A significant percentage of that cost is attributable to compressor valves.
Although liquid, dirt, or process contaminants often cause valve failures, design factors are often a major contributor. Furthermore, valve design can also reduce the effects of contamination in some cases. Valve life in some severe services has been as short as 4 days when the wrong combination of valve lift and materials was specified.
Although new materials and a better understanding of valve dynamics have greatly improved reliability, valves continue to have a major impact on overall compressor availability. For example, a large refinery compressor shut-down for valve replacement reduced the plant feedrate by 40%, which cost $65,000 (1990 dollars) in lost production. Even small improvements in valve life which postpone valve repairs can have an a large impact on plant profitability.
There are many types of compressor valves. Almost all are spring loaded and gas actuated. Reciprocating compressors generally used one of the three basic valve configurations: plate, strip, or poppet. These are described in the following paragraphs.