Page 353 - Reciprocating Compressors Operation Maintenance

338 Reciprocating Compressors: Operation and Maintenance

One day, a situation arose where the 100 HP compressor was shut down
because it could not produce pressure. The 40 HP machine could not oper-
ate because of a highly audible noise.
A service person was dispatched to investigate the situation. The fol-
lowing are abbreviated entries from his notebook.

A. Checked 100 HP unit by opening discharge valve to pressurized sys-
tems (with compressor shut off). Crankcase pressurized (single-act-
ing compressor) which indicated bad discharge valves and possibly
worn or broken piston rings.
B. Checked 60 HP compressor by running and blocking off system and
venting discharge to atmosphere, while maintaining 100 psig dis-
charge pressure. Checked full-load amps, which were at 98% design.
Therefore, this compressor at near full capacity of 300 CFM.
C. Checked 50 HP compressor the same as B, This unit also at full
capacity or 250 CFM.
D. Checked 40 HP compressor by running to maximum design pressure
(100 psig). Unit leaked severely at packing gland and could not be
adjusted to correct. Unit also had loud rap or knock. Unit could not
develop 100 psig, due to severe leaks. Required extensive repairs to
cylinder and running gear.

Of the total 1250 CFM capacity, system would only produce 550 CFM,
CAPACITY REQUIREMENT DETERMINED

At lunch time, the entire plant was shut down with no compressed air
requirements. Both the 60 HP and 50 HP compressors were placed in
operation to pressurize the system to 100 psig. But, only a maximum pres-
sure of only 60 psig could be attained. A short walk through the plant
revealed air leaks near every air user. The result was that over 100 HP was
required to maintain the leaks in the plant. (If 100 psig was to have been
maintained during this shutdown, precisely 110 HP was required to over-
come the leaks).
The plant required at least 160 HP of compression to maintain 100 psig
during plant operation. Without leaks, however, this plant required only
40 HP, or about 200 CFM.
The cost of this wasted energy is easy to calculate.