Emerson Anderson Greenwood 93 Series Installation And Maintenance Instructions Manual page 2

ANDERSON GREENWOOD SERIES 93T PILOT OPERATED SAFETY RELIEF VALVES
INSTALLATION AND MAINTENANCE INSTRUCTIONS
External
blowdown
adjustment
Outlet
Main valve
(typical)
FIGURE 1
1.3 Start-up
There must be pressure at the valve inlet
to establish a differential in force across
the diaphragm and "load" it in the closed
position. Pressure must pass through the pilot
supply tube and pilot, and exert force on the
diaphragm. On normal start-up, the valve loads
itself without incident as pressure increases.
Block valves are often used under safety valves
in order to isolate them when maintenance
is required. When putting the safety valve in
service be sure the block valve is fully opened.
If the block valve is opened after system start
up, the safety valve, may briefly vent to the
atmosphere before the dome gets pressurized.
It will then close off positively.
2 MAIN VALVE MAINTENANCE (REFER TO
FIGURE 2)
2.1 Disassembly
Remove the cap bolts, lift the cap from the
valve body and lift the diaphragm, seat and
guide from the valve. Remove the seat bolt(s) to
separate the diaphragm from the seat, guide,
and retainer plates.
2.2 Repair
Inspect the nozzle seating area for nicks or
scratches. If they cannot be removed with
crocus cloth or fine sandpaper, the nozzle must
be remachined. The nozzle may be removed
from the body. Machining of the 93T nozzles
should be limited to .06" material removal since
the diaphragms used in these valves have a
shallow dish.
To replace the film seat, remove the retainer
screws and ring and lift the primary film seat
and secondary seat from the seat plate. Install
a new film seat by placing the film over the
seat plate with the edges of the film extending
beyond the outside diameter of the plate. Place
the secondary seat on the film and the retainer
with those in the seat plate and press the
retainer down evenly over the seat plate ridge.
Pilot valve
Supply tube
Nameplate
Inlet
Larger size valves may require that the retainer
be pulled into place with the retainer screws.
Start several screws in opposite holes using the
screws to pierce through holes in the film and
tighten one thread at a time.
Note: the film must be stretched tight and
be free of wrinkles and scratches to insure
a bubble tight seal.
Install the remaining screws in the seat
retainer, trim the excess film from the outer
diameter and cut a hole in center for the
seat bolt.
2.3 Assembly
Reassemble the diaphragm, seat and guide in
the reverse order of disassembly. Apply a light
film of lubricant to all threaded parts. Care
should be taken to adequately tighten the seat
bolt(s) on those valves with guides to prevent
the diaphragm from pulling away from the bolt
under pressure.
Note: the 8", 10" and 12" main valve
diaphragms have a ¼" diameter hole in the
center to allow dome pressure to pressurize
the film seat. Make sure all replacement
diaphragms have this hole. If the film seat
is not pressurized, the main valve seat will
seal off.
Carefully insert the guide squarely into the
nozzle and lower the diaphragm assembly into
place. Align the holes on the diaphragm O.D.
with those on the body. The body seal gasket or
ring is placed between the diaphragm and body.
Replace the cap and bolts and cross-torque
bolts to 50 ft·lbs.
Refer to paragraph 8 for Soft goods repair kits.
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