8
Flow Control Division
Edward Valves
The guides must be close enough to bring
the disk accurately down into the seat to
make a tight joint.
Fig. 160
Screwed-Cover, Cover-guided Ball Check,
Screwed-in Set
Foreign material in the flow medium may
wedge between guiding surfaces with the
possibility of making the disk stick. It is
recommended that piston check valves be
used where the fluids are clean and where
tight seating is important. In smaller sizes,
it is recommended that ball type check
valves be used where the problem of stick-
ing open is of serious consideration. Valves
sized too large for flow condition will
sometimes have excessive wear, chatter
and noise.
Backseat
Edward stop valves have a backseat inte-
gral with the bonnet. The seating face on
the bonnet is generally a bevel and the
seating surface on the disk, disk nut, or
stem is provided with either a radius or a
bevel. Care must be taken of sealing sur-
faces on both the bonnet and the radius,
which seals against it to obtain a tight
backseat.
Integral Backseat Construction
Packings
Edward valves are packed with all-purpose
packing sets. This is a combination of
packing using braided rings at the top and
bottom of the packing chamber and flexi-
ble graphite packing in the center section.
Packing glands should be tightened down
enough to prevent leakage but not enough
to develop excessive operating torque.
When the gland has advanced approxi-
mately half way into the packing chamber,
it is recommended that additional packing
rings be added. To obtain best results, the
stem should be thoroughly cleaned.
Replacement packing should be the same
as that originally furnished. Edward valve
packings are inhibited to prevent stem
pitting in service.
We recommend packing be purchased
from Edward Valves to assure packing with
the proper density and corrosion inhibitors
is always used.
IMPORTANT:
• Long service life from modern
graphitic packing requires that ade-
quate preloads be applied when
repacking.
• All parts should be clean and not
scored or pitted, especially the stem.
• The stem, disk and bonnet should be
in the valve prior to installing the new
packing.
• Position split packing with the ends of
adjacent rings rotated 90°.
• Standard packing
Top Ring Braided Ring
Center Ring Flexible Graphite Ring
Bottom Ring Same as top
• Clean and lubricate the gland bolts.
• Tamp the packing down by hand
using the gland.
• IMPORTANT: Apply the recommended
torque to the gland nuts evenly with-
out cocking the gland. See table.
• Tighten nuts to the initial values
shown, then loosen and retighten to
the final range.
• Stroke the stem and then recheck the
torque on the gland bolts.
Backseat and Packings
(40 paginas)
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