Page 351 - Reciprocating Compressors Operation Maintenance
P. 351

336    Reciprocating Compressors: Operation and Maintenance


         Symptom:  A recently  overhauled,  horizontal  two-stage  compressor
           developed a noisy suction  valve.
         Problem: The  gasket  under the suction valve had  been  left  out making it
           loose on the seat.
         Question:  When  intercooler  pressure  indicates  a  leaky  or  broken  com-
           pressor  valve, how do  you  tell which one  is defective without remov-
           ing all valves?
         Answer:  Leaking  valves  can  be  detected  by  cover  temperatures  that  are
           somewhat greater than others, or by a slight difference in valve  operat-
           ing  sound, or by both of these symptoms.
         Question:  How  can  the  discharge  temperature  indicate  the  compressor
           mechanical condition?
         Answer: A compressor,  operating  under  the  same  air  pressure  and  cool-
           ing  water temperature,  should  register constant  discharge  air  tempera-
           ture. If the latter increases while the other  conditions remain  constant,
           leakage  is definitely  indicated, usually  of the hot discharge back  to an
           intermediate pressure.  It may  be either  valve or piston  ring  leakage. A
           plant  log  recording  interstage  pressures  and  temperatures  should  be
           regular  practice,  because  it  definitely  notifies  the  operator  when  to
           examine piston  rings  and valves. An increase in discharge  temperature
           also puts him on  guard concerning  the  mechanical  condition  of a sin-
           gle-stage  compressor.
         Question:  What  causes  discharge  air  temperature  to  increase gradually
           and  the cylinder  to become  somewhat  hotter  than formerly,  when  pis-
           ton  rings  and  valves  are  in  first-class  condition  and jacket water tem-
           perature is normal?
         Answer: After  years of operation,  if jacket water quality is not particular-
           ly  good,  the jacket  cooling  effects  may have deteriorated  considerably.
           The inside of jacket  walls may be covered  with heavy deposits of lime
           or magnesium,  which interferes  with normal  heat transfer. The  answer
           of course, is to thoroughly clean the jacket.

         SERVICE  CONDITION  CHANGES

           A  change  in  suction  or  discharge  pressure  may  cause  problems.
         Observing these pressures  should be part of any troubleshooting  effort.
           A plant operator  advised  that he  had purchased  a  12 x  9  single-stage
         horizontal  compressor  and  that  he  was  using  it  for  100 psi  pressure.  He
         inquired  about the  working conditions for  which this machine  was suit-
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