Page 388 - Reciprocating Compressors Operation Maintenance

Safety in Operation and Maintenance 373

installations. A double block and bleed valve combination is satisfactory
if the bleed line (for example, a vent line to atmosphere) consists of more
than small-diameter tubing. Remember, very high pressures are held
back by the block valve. If there is leakage around a gate or plug in a
valve, a small vent line may not be able to fully bleed down the line. This
can result in gas leaking through the second block valve into the com-
pressor room.

REPLACEMENT BOLTS AND TORQUE

Another problem occurs if the replacement bolt and nuts are of a differ-
ent hardness and steel composition. Compressor manufacturers specify
nut and bolt properties. They also specify torque values aimed at evenly
distributing the load on ail nut-bolt connections. Impact wrenches are able
to exert enough tension on the bolts to cause the cast iron casing to crack!

DISASSEMBLY/ASSEMBLY

Disassembly should not be undertaken with tools such as crescent
wrenches, pipe wrenches, cheater bars, or worn/incorrect size tools.
Many compressors require special tooling for disassembly and assembly.
During assembly, all clearances should be double checked and record-
ed. All bolts and nuts must be rechecked for tightness. Internal areas of
the cylinders and running gear must be free of any fasteners, tools, rags,
or other foreign material.
Oil systems must be flushed and verified to be clear. Cleaning of oil
sumps or crankcases should be done with lint-free rags and vacuumed
clean. With clean oil installed and the compressor prepared for start up,
manually turn over the unit to check free rotation. Manually (or remote-
ly) run cylinder lubricator to furnish ample oil to cylinder and packings.
Large compressors require frame oil circulation. Electrically bump unit
to check rotation. Start up to less than full speed and shut down. Check
conditions. Start up and run in accordance with manufacturer's start-up
procedures. Again verify that all conditions are as anticipated.

Thorough cleaning and inspection often reveal problems that would
not normally have been expected. During the inspection and repair pro-