Page 220 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

202 Major Process Equipment Maintenance and Repair

held open or leak, they will burn during the combustion and expansion
periods, and compression pressure will charge the inlet jumper and
header with air. When the gas valve does open, the gas charge is diluted
with air or burned combustion gases.

Cylinder Heads-Cracking of cylinder heads is a problem that does
not often occur, but when it does it is costly. In certain installations, a
given cylinder head design may be subject to cracking problems, while in
other types of installations the problem may be totally nonexistent even
with the same head design. (This comment, naturally, does not apply to
those installations where engines are subjected to long periods of over-
load and heavy, continuous detonation.)
In many instances, design and operation of cooling-water systems have
been found to contribute to cylinder head cracking. It is known that, in
controlling temperatures, if the spread between inlet and outlet of the en-
gine exceeds 15"F, cracked cylinders, heads and/or exhaust manifolds
are quite likely to show up. It is also reasoned that if adequate provisions
for removing entrained air are not made, cracked heads are likely to ap-
pear. Some designers use traps in the high locations, while others contend
that a vented standpipe which will slow the water to 0.5 ft per second is
required to release the air. The relationship between entrained air and
cracked heads is difficult to determine but air appears to have been a con-
tributing factor in many failures.
Ignition-Space is too limited here to cover this subject in detail, but it
is so important that a few words of advice will have to be included. Ev-
eryone knows that faulty ignition can contribute to most of the failures
mentioned earlier. The problem is that not everyone has the necessary
equipment to quickly analyze and locate the trouble. An operator can, by
the process of elimination, find the trouble in a one- or two-unit installa-
tion. However, in multi-unit installations, it is difficult to keep ahead of
troubles in magneto or interruptor systems without costly instruments.
About all that a person can do without these instruments is make sure that
the plugs, points, coils, condensers, gap settings, battery voltage,
grounds, connections and wire insulation are satisfactory. This, of
course, can be accomplished visually or by simple tests.
The ignition analyzer is recommended as a very valuable instrument
for checking out ignition system components. These instruments, of
which there are a number on the market, are highly versatile and can be
used with pressure pick-ups to locate such varied troubles as bad valves,
rings, pistons, etc., in both the power and compressor areas. Although
some companies feel they cannot justify the cost of an analyzer and the
man-hours required to operate the unit, analyze readings, and keep rec-
ords, experience shows that this cost is well paid for in the reduction of