Stuffing box
• The crankcase is separated
from the cylinder and
scavenge space in a two
stroke crosshead engine by a
diaphragm plate. Hence a
provision can be made here to
prevent the lube oil from being
carried upwards from the
crankcase; used cylinder oil
contaminated with products of
combustion from being carried
downwards into the crankcase
and the pressurized scavenge
air from leaking into the
crankcase. For this the piston
rod is made to pass through a
stuffing box, bolted on to the
diaphragm plate.
• The stuffing box casing is
split vertically into two
parts. It carries a series of
rings, which are made up
in three or four segments.
On the outside of each
set of segment, is a
garter spring. This
provides the tension to
hold the ring segment
against the piston rod.
There is clearance
between each segment to
allow for wear. The rings
are made of either bronze
or cast iron lamella, fitted
in replaceable steel
backing ring.
• As the piston rod passes up
through the stuffing box, the
lube oil from crankcase is
scraped off by the lower set of
rings and drained back to the
crankcase though drillings. Any
lube oil that passes this
primary set is scraped by
another set of rings and is led
through a drain to a piston rod
drain tank. As the piston rod
passes down through the
stuffing box, the top set of
rings will scrape off the
contaminated cylinder oil to the
bottom of scavenge space,
where it is drained via the
scavenge space drains.
However, if these rings are
worn out, then the
contaminated cylinder oil will
drain to piston rod drain tank.
• Regular maintenance of the
stuffing box will keep it in good
condition. Checking the
scraping rings butt clearances
and garter springs tension and
replacing the worn out rings
are all part of the overhaul
procedures. Excessive wear
will take place if the crosshead
guides are out of alignment or
the guide clearances are
excessive. Worn stuffing boxes
and excessive leakages can
exacerbate the incidence of
scavenge fire and increase the
risk of crankcase explosion.