Page 200 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

182 Major Process Equipment Maintenance and Repair

4. In multi-stage machines, check the load chart before operating
valve lifters or unloading pockets.
5. Never bypass gas between stages unless the equipment is designed
to operate that way.
6. When a relief valve blows, shut down and determine the cause.
7. Don’t start a unit against discharge pressure.

Accelerated wear or scuffing. Normal wear of pistons, rings, liners,
packing and rods is not a significant problem. Generally, the normal life
of those parts is long and satisfactory. Furthermore, this type of wear is
gradual and can be observed or detected by progressive fall-off of capac-
ity. Accelerated wear, scuffing and sudden seizures, however, amount to
a major portion of over-all compressor expense because they come dur-
ing peak periods and when least expected. Yet these failures are for the
most part avoidable because there is a precise way of spotting them, even
while the machine is running.
The key to the check is the vent line (3) in Figure 5-6. Figure 5-6 is a
section through a typical pressure packing compartment. The oil supply
line (1) enters the compartment and connects to the packing flange (2).
Oil is directed from the flange to the front end of the packing. The vent
for the packing comes out of the bottom of the flange and is piped to the
outside by the vent line (3), to the end of which a valve (4) is attached.
On low-pressure cylinders very little, if any, vapor will come out the
vent when the packing is sealing, but a good portion of the oil that is
being fed to the packing will drop out of the valve (4).
On high-pressure packing, there will be some vapor even if the packing
is sealing. The vapor will have a higher velocity and will contain an oil
mist.
It is very important that the amount and velocity of vapor emitted from
the line be observed while the packing is in good condition. The color of

Figure 5-6. Section through reciprocating
compressor pressure packing Compartment.