Operating & Service Manual 10 OPS-804 Rev.01
2)
Back Seat Stem
– Valve in Open Position
a)
Open valve fully and rotate hand-wheel counterclockwise about 2 turns to allow sufficient clearance for
the stem/gate assembly to move up against the bonnet back seat profile when the bonnet cap is back
off.
b)
Remove set screw on the bonnet cap. Mark location and back off bonnet cap 3 full turns. If there is
sufficient line pressure in the valve the stem could be seen rising as the bonnet cap is back off. The
stem would stop the upward movement once the back seat taper on the stem comes into contact with
the matching profile in the bonnet. If no line pressure is present, an upward heave on the hand-wheel
would similarly raise the stem.
c)
Remove the cap on the injection fitting (located on the bonnet) careful not to inadvertently backing off
the fitting by applying a back-up wrench if necessary. Install a cap stinger to the injection fitting and
slowly make up to depress the ball-check to bleed off any pressure trapped in the packing cavity of the
bonnet. If no further pressure is bleeding off than the stem back seat is verified to hold pressure.
WARNING:
In the event of continuous pressure bleeding, back off the bonnet cap another full turn in case the
stem has not moved up far enough to coin a seal in the bonnet. If this still does not stop the pressure
bleed off indicating the stem back seat is unable to hold pressure, quickly retighten up the bonnet
cap the same number of turns back to its original marked position and re-install the set screw.
In this situation the valve must be removed from service to replace the stem packing or the line
pressure must be completely isolated if the valve cannot be remove.
d)
Proceed to remove hand-wheel, bonnet cap and bearing assembly. While doing so careful not to
accidentally push or exert any force on the stem as it may inadvertently unseat the stem back seat.
Carefully unscrew packing gland. Remove the stem packing. One easy way is to blow air or pump
grease through
the injection fitting to “pop” the packing out of the bonnet.