Abu Dhabi Gas Liquefaction Company Ltd Job Training Mechanical Technician Course Module 9 Compressors

7 Compressor 
Maintenance 
Because of the similarity between compressors and pumps, most of what was said 
about maintenance in the Pumps module also applies to compressors. Most of the 
items that you should check for damage and items that can be repaired or replaced are 
the same. 
Reciprocating compressor valve construction is different. The sealing surfaces are 
usually formed between very flat plates. Valve lapping is done on a rotating lapping 
table shown in Figure 7.1. 
Centrifugal compressors make more use of labyrinth seals and these are used in place 
of the wear rings used in pumps. 
Mechanical seals used in compressors can be more complicated than those used in 
pumps. They often use gas at high pressure instead of, or as well as liquid to stop 
product gas from escaping. These are described in the Seals module in this course. 
Figure 7.1: Valve-lapping Table 

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8 
P&ID and PFD Symbols for Compressors and Auxiliaries 
Most ADGAS PFDs and P&IDs use one symbol for all types of compressors.
Intercoolers and aftercoolers are both types of heat exchanger. No special symbols 
are used for these. 
Snubbers and knockout drums are shown as vessels or drums. 
Table 8.1 shows these symbols. 
Equipment 
Symbol 
Compressor
(Note that flow enters at the larger end 
and leaves at the smaller end to show 
compression of the gas) 
Intercooler 
Aftercooler 
(Heat exchanger symbols)
Snubber 
Knockout drum; scrubber; 
separator; suction and 
discharge drums 
(Drum or vessel symbols)
Table 8.1: Compressor and Auxiliary Equipment Symbols 
Horizontal 
Vertical 

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Job Training—Mechanical Technician 
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