head. Make sure that the buffer spring is
centred by the cover. Pull the cover with the
nuts on the long studs so far down that the
other studs
sufficiently project beyond the cover.
n) Screw the nuts onto the other studs and firmly
tighten them.
p) Purge the compressor (refer to par. 9.9).
REMARK!
In order to reduce the downtime involved in this
valve inspection, it is recommended to have as
many complete valve assemblies in stock as there
are cylinders on the compressor.
The valves can then be exchanged with the valves
to be checked; the original valves can then be
inspected at leisure and, if necessary, repaired or
replaced.
9.9 COMPRESSOR PURGING
When the compressor has been opened for
carrying out maintenance operations, it must be
purged before being put into operation again.
Purging can be effected by means of the
compressor itself, whereby the situation after
compressor evacuation is taken as a starting point.
The procedure is as follows :
a)
For compressors equipped with capacity control:
Cut out as many cylinders as possible.
b) Start the compressor; the air in it is now blown
off via the line disconnected during evacuation
at the lower side of the discharge pressure
safety switch.
c) Cut in the other cylinders step-wise as soon as
the suction pressure has dropped considerably,
and wait until the suction pressure ceases to fall
or the oil lubricating pressure safety switch
becomes operative.
MIND! Immediately stop the compressor as
soon as the oil lubricating pressure (i.e the
difference between oil pressure and suction
pressure) becomes lower than 1 bar.
d) Reconnect the line to the discharge pressure
safety switch. When the discharge pressure
increases, the line must be disconnected again.
As soon as the discharge pressure no longer
increases, the line can be connected permanently.
e) Stop the compressor and remove the shunting
of the electric contats of the suction pressure
safety switch.
f) Open the discharge valve and watch the
discharge and suction pressure gauges,
particularly if maintenance operations have
been effected on the valves. Only the discharge
pressure gauge may rise; if also the suction
pressure gauge rises distinctly, this is indicative
of leaking valves due, for instance, to their
incorrect assembly.
If necessary, remedy this defect.
g) Start the compressor and slowly open the
suction stop valve (mind liquid hammer!).
h) Open the shut-off valve in the return line of the
oil separator.
j)
For two stage compressors:
open the shut-off
valves in the liquid lines of the interstage cooler.
k) Keep the compressor running for some minutes.
l) Purge the refrigerating installation (refer to
plant manual).
Refrigeration Division
Grasso
9. COMPRESSOR MAINTENANCE
v003.98.11.en
Refrigeration Compressors Series RC9
Page 9.5