It is empathetically pointed out that assembly of the
valves should be carried very carefully. Incorrectly
assembled valve will immediately give rise to trouble.
When valve components are replaced; it is important to
make a note of the date in the compressor logbook so
that ready check is available to indicate when valve
rings and springs required renewal.
7.4 SAFETY VALVES :
The safety valves should be inspected only if they are
leaking. They should then be disconnected and cleaned.
Upon reassemble they should be light oiled with the
same oil as used in compressor.
The compressor must on no account be kept running
with an open-or-leaking safety valve as the machine
would then become too hot and the possibility of
damage or to even seizure of the piston and cylinder
liner would arise. The line on the suction side of the
safety valve should be cold when the compressor is
operating. When it is found warm the safety valve is
leaking thus causing loss of capacity, in this case the
safety valve must be repaired or renewed.
7.5 PISTON RINGS:
The piston and scraper rings should be inspected after
6,000 hours ,running for gap clearances. The gap should
not be more than 1.3 mm, otherwise replace the piston
rings. (This checking to be done in cold condition & also
piston/scraper/oil rings to be fitted properly in liner
which is good in condition.) These rings must never be
removed from the piston if not strictly necessary. Only
when it is essential they should be removed, and then
only with the correct ring removal tool. When used, but
undamaged, rings are fitted to the piston, it is essential
that each ring should be replaced in its original ring
groove. This operation must always be carried with the
aid of correct ring fitting tool. When fitting a complete
new set of piston rings, the chromium plated one must
always be fitted in the topmost groove of the piston.
Measuring the piston ring clearance can also be carried
out by pulling up the piston so that the ring to be checked
is visible in the top of the cylinder but still remain in it.
The gap clearance can then be measured with a feeler
gauge.
7.6 BEARINGS:
All the bearing should be inspected after 9,000 hours
running. When a main bearing bush located In either of
the end covers requires renewal, particular attention
should be paid to ensure that it is inserted absolutely true
to the center line of the housing bore. If it is introduced
even slightly out of center, it will become distorted and
will remain so even if forced for full length into the
housing. It is therefore essential that the bush should be
pressed into the end cover. with both the bearing cover
and the bush itself held true between the parallel faces of
a press.
A locating pin is fitted in the end face of both end cover
bearing bushes, thus preventing it from rotating, the
main bearing bushes are provided with an oil
distribution well and when the end covers are fitted to
the compressor it must be ensured that this well lies in a
position 450 from vertically upwards position measured
in the direction opposite to the rotation of the $haft.
While assembling the connecting rods on the
crankshaft, full attention should be paid to tightening of
the connecting rod bolts. These bolts should be so
tightened that both the connecting rod halves touch each
other.
7. PERIODICAL MAINTENANCE AND ITS
SCHEDULE:
7.1 The compressor, like any other machine, requires
regular maintenance. If it is maintained well, the cost of
this work is recovered for the most part through
improved performance. It is therefore recommended to
follow the instructions as strictly as possible. There is,
however no objection in carrying out the following at
times other than indicated, provided the periods
between do not exceed the stated number of hours. It is
necessary to inspect the compressor completely every
year, irrespective of the number of hours it has run.
When it is necessary to work on the compressor, the
machine must always be evacuated beforehand.
7.2 PERIODICAL INSPECTION :
Periodical inspections should be made during the
normal shut-down periods as much as possible, so that
the compressor is always available for operation when
required. If, at the time, the total number of hours
running differs somewhat from the figures quoted in the
maintenance schedule, the inspection should
nevertheless be carried out. In this way it will not be
necessary to have to stop the compressor at an
inconvenient time. The number of running hours
between these inspections have been established in such
a way that the inspection of several items coincides and
may be carried out simultaneously. The procedure will
keep the maintenance cost as low as possible.
7.3 VALVES:
Dismantle the valves completely for inspection
purposes after the first 500 hours' running.
Subsequently, after every 4,000, 4,500 hours' running.
Even for the slightest damage to the valve rings it is
advisable to renew them. Damaged valve seats must
also be repaired or renewed. If the seat face lips are only
slightly damaged, they can be repaired by grinding with
a very fine abrasive compound, using a completely
smooth glass plate. Heavily damaged seats must be
turned off on a lathe and lapped. In order to maintain the
correct valve lift, the chamber of the delivery valve, in
which the stroke limiter centres, must be turned out. As
this work is specialized, it is recommended that it should
be done by the supplier.
Before reassembling the valve, all the parts should be
cleaned and dried carefully. Then these should be lightly
oiled, with the same oil as used in the compressor. After
reassembling, check that the valve rings can be pushed
up flat against the stroke limiter, Only in this way the
correct assembly of the valve rings and spring is
ensured.
It is recommended to have as many complete valve
assemblies in stock as there are cylinders. This will
considerably reduce the shutdown period of the
compressor during routine inspection of the valves,
since complete valve assemblies can be fitted directly to
the compressor in place of the original valves. Those
removed can be inspected at leisure and repaired as
necessary, once the compressor has put back into
operation with the new valves. Spare parts should also
be available in order to completely renovate damaged
valves. All valve rings and spring must be renewed after
about 9,000 hours running.
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