Page 203 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Reciprocating Gus Engines and Compressors 185

maintenance falls into the routine category. For that reason, comment
will be divided between the two different phases.

Packlng Maintenance

At start-up or after overhaul, one inspection cover (if provided) should
be removed from the compartment between the crosshead guide and the
compressor cylinder. If this compartment is filled with vapors from the
pressure packing, there should be concern, because the rod and packing
are hot and some action will have to be taken. This is a point uver which
there is considerable controversy: one school of thought holds that the
packing oil feed rate should be increased to its maximum, contending that
the added oil both cools and seals; the opposing view is to momentarily
cut off the oil supply, on the assumption that the packing will thus seat
faster. We, however, agree with neither extreme-the added oil inside the
packing is not enough to cool; and if dirt was the cause of trouble or if the
material has started to cut, the extra oil will make a slurry of carbon and
sludge in the cups. We have never eliminated the problem by increasing
the amount of oil, but have had some success in reducing the feed rate to
what it should have been in the first place. However, anything that can be
done to cool the rod-by pouring oil, directing an air stream or even wa-
ter on it as it comes out the packing-might hold the temperature level
down long enough for the materials to seat. Where it is possible to reduce
the speed of the unit or decrease pressure until seating starts, this will
help too.
These are only temporary measures, and if the vapors increase the unit
should be shut down and the entire assembly checked, cleaned, and per-
haps lapped. This vigilance is vital, because the rod is bound to score,
and not only are new rods expensive, but delivery on them sometimes is
not very prompt.
During the period of heavy vapors and the state of confusion on go or
no-go, any scuffing or roughness of the rod can be felt while the machine
is running. Naturally, there will be marks or streaks on the rod, but if it is
smooth, hold off shutting down. If scuffing starts, shut down immedi-
ately.
Once it has been established that there are no vapors in the packing
compartment, the inspection cover can be replaced, but the packing vent
line should be watched. Any increase in vapor will indicate packing scuf-
fing. As mentioned before, the color of the oil from the vent will be an
indication of the liner and piston condition. If the vent packing oil begins
to darken and a check on the liner is satisfactory, then the scuffing is orig-
inating in the packing. In multi-stage air machines, there is water fallout
after the second stage. Separators are installed before the suction of those