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ANDERSON GREENWOOD TYPE 91 AND 94 PILOT OPERATED SAFETY RELIEF VALVES
INSTALLATION AND MAINTENANCE INSTRUCTIONS
1.3 Start-up
There must be pressure at the valve inlet to
establish a differential in force across the
bellows and "load" it in the closed position.
Pressure must pass through the pilot supply
tube and pilot, and exert force in the bellows.
On normal start-up, the valve loads itself
without incident as pressure increases.
Block valves are often used under safety valves
External blowdown
adjustment
Main valve (typical)
FIGURE 1
2 MAIN VALVE MAINTENANCE
Refer to Figure 2
2.1 Disassembly
Remove hex bushing from guide tower, then
remove cap from body by lifting cap vertically
until guide tower disengages the guide tube on
the bellows. Turn cap assembly upside down
to remove drag ring assembly on those valves
where it is used. It is not necessary to remove
guide tower from cap unless one of these parts
is to be replaced.
Lift bellows assembly with seat from body.
Remove guide bolt to separate guide and
seat plate from bellows. The bellows shield,
where used, can now be removed. Remove seat
retainer from seat plate and PTFE seats.
2.2 Repair
Clean all metal parts, and replace seat and
seals, as required. The nozzle may be removed
from the body if it cannot be adequately cleaned.
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 over the secondary seat.
Align the holes in the retainer with those in
the seat plate and press the retainer down
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
before the dome gets pressurized. It will then
close off positively.
evenly over the seat plate ridge. 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 screw 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 guide bolt.
Pilot valve
Supply tube
Nameplate
2
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