Emerson Crosby HSJ Series Installation, Operation And Maintenance Instructions page 7

Crosby SerieS HSJ Safety valveS
InstallatIon, operatIon and maIntenance InstructIons
repair procedure
all the parts should be cleaned thoroughly.
Guiding surfaces may be polished using a fine
emery cloth. all parts should be examined to
determine their condition. inspection of valve
components is important to ensure proper
valve performance.
Damaged valve parts must be repaired or
replaced. Parts identification may be found in
figure 1 on page 2.
lapping or refurbishing of valve seats
Good seating surface on the nozzle (2) and disc
insert (6) or disc (6a) are of the greatest
importance when reconditioning the safety valves.
the seats should be flat and free from surface
scratches.
lapping block
lapping blocks are made of a special grade of
annealed cast iron. there is a block for each
orifice size. each block has two perfectly flat
working sides and it is essential that they retain
this high degree of flatness to produce a truly
flat seating surface on the disc, or disc insert
and/or the nozzle.
Before a lapping block is used, it should be
checked for flatness and reconditioned after
use on a lapping block resurfacing plate. the
block should be lapped in a figure eight motion,
applying uniform pressure while rotating the
lapping block against the plate as shown in
figure 3.
lapping blocks and lapping block resurfacing
plates are available from emerson sales,
service and distribution centers.
lapping compounds
experience has proven that medium coarse,
medium, fine and polish lapping compounds
will condition any damaged safety valve seat
properly except where the damage requires
machining. the following lapping compounds,
or their commercial equivalents are suggested:
table 1
grit compound no. description
320 Medium coarse
400 Medium
600 fine
900 Polish
lapping procedure
unless the seats have been damaged badly
by dirt or scale, lapping the seating surfaces
should restore them to their original condition.
Never lap the disc insert or disc against the
nozzle.
lap each part separately against a cast iron
lapping block of the proper size. these blocks
hold the lapping compound in their surface
pores and must be reconditioned frequently.
lap the block against the seat. Never rotate
the block continuously, but use an oscillating
movement. extreme care should be taken
throughout to make certain that the seats are
kept perfectly flat.
if considerable lapping is required, spread a
thin coat of medium coarse lapping compound
on the block. after lapping with this compound,
lap again with a medium grade compound. the
first step can be omitted unless much lapping
is called for.
Next, lap again using a fine grade compound.
When all nicks and marks have disappeared
remove all the compound from the block and
seat. apply polish compound to another block
and lap the seat.
as the lapping nears completion only the
compound left in the pores of the block
should be present. this should give a very
smooth finish. if scratches appear, the
cause is probably dirty lapping compound.
these scratches should be removed by using
compound free of foreign material.
Discs and disc inserts should be lapped in the
same way as nozzles. the disc insert must be
removed from the holder before lapping. Before
the disc insert is placed back in the holder all
foreign material should be removed from both
parts. the insert must be free when in the
holder. if the disc insert is damaged too badly
to be reconditioned by lapping, it should be
replaced. remachining the insert will change
critical dimensions, affect the action of the
valve and is not recommended.
machining of nozzle seats
if machining of the nozzle seat or other major
repairs are necessary it is recommended that
the valve be returned to a emerson authorized
facility for repair. all parts must be machined
accurately per emerson specifications. No
safety valve will be tight, nor will it operate
properly unless all parts are correctly
machined. if unable to a return to a emerson
authorized repair facility for remachining, use
of a reseating machine is recommended.
fiGure 3
Motion shown
by dotted lines
Bottom rough
surface do not use
lapping block resurfacing plate
lapping block
top lapping
surface
lapping block
to be squared up
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