Flowserve V-377 R4 Edward Valves - Manual (Page 12)

12
Flow Control Division
Edward Valves
Body Wall Leak
This is a visual leak through the body wall,
welding end or end flanges and may be the
result of a shrink cavity or other void in the
casting. If small at first, such a leak may go
unnoticed for a time, particularly if the valve
is heavily insulated and the pipe line at that
point is sufficiently warm to keep the insula-
tion dry enough to escape notice.
Objectionable Vibration, Noise or
Excessive Pressure Drop
Excessive vibration noise or humming com-
ing from within a stop-check, non-return or
check valve indicates the possibility that
the disk-piston assembly is wedged inside
the body. Such sticking may be caused by
uneven body guide rib wear on the down-
stream side induced by oversizing the
valve, or by corrosion, by flakes of line
scale, or by particles of weld spatter that
may have entered the valve during con-
struction of the piping, and which later
washed up into the piston bearing area of
the body I.D.
On stop-check and non-return valves, the
stem position is indicated by the stem
guide collar on non-revolving stems, or by
the position of the handwheel on revolving
stems; the stem should normally be fully
open against the bonnet backseat in order
that the disk-piston can lift the full amount.
When the disk is not touching the bottom
of the stem or the bottom stop lugs on the
bonnet (due to a wedged disk-piston or
insufficient flow, for example), then the disk
assembly is free to move laterally within
the body. This motion in most cases causes
a slight vibration which can be felt through
the body, yoke and handwheel.
Screwing the stem down slowly to contact
the disk first increases the intensity of vibra-
tion to the hand and to the ear, but further
downward, movement of the stem builds
sufficient contact pressure and eliminates
the vibration. This also tends to dislodge
any foreign particles that may have been
the initial cause for disk-piston wedging.
The position of the lift indicator on the
yoke, where vibration ceased, should be
noted and any increase in pressure drop
indicated on available gauges recorded. It
may be that when the stem is screwed
back to the full open position, the disk will
again remain in a floating position, which
could indicate oversizing of the valve for
the flow conditions. It is always recom-
mended that check valve size selection be
governed by flow conditions rather than by
adjacent piping. Oversizing induces vibra-
tion or noise and causes excessive, uneven
guide rib wear, giving rise to greater disk-
piston assembly clearance on one side of
the body.
By means of other valves in the line, it may
be possible to vary the rate of flow through
a noisy check valve sharply enough (in a
short period of time) to dislodge the piston
from its wedged position.
Valve Lubrication
In order to obtain full service life, valves
require periodic lubrication of the bearings
and stem threads, as does any rotating
machinery.
On valves where the stem bushing and
bearings are in the motor operator, the
bearings are lubricated by the operator
lube supply, which should be maintained
at the recommend level.
Valves that have bearings in the top of the
yoke have lube fittings on the valve yoke
for convenient relubrication.
Stem threads also require periodic replen-
ishment of the lubricant. Exposed threads
should be wiped clean of old grease and
accumulated dirt and fresh lubricant
applied. This can be most effectively done
with the valve in the closed position.
For valves that see frequent operation, the
lubricant should be replenished on bear-
ings and stem threads every three months.
If extreme service conditions dictate, the
plant operating engineer should establish
a more frequent relube schedule.
For valves that are operated infrequently,
relubrication at least once a year is recom-
mended. The recommended lubrication for
both bearings and stem threads is Rykon EP
#2, manufactured by The American Oil
Company. This is an extreme-pressure,
extreme-temperature lubricant of high
quality.
Valves equipped with automatic stem lubri-
cators should be maintained in accordance
with the above instructions for the bearings
and as required to maintain the lube level
in the stem lubricator reservoir.
Service Problems
(continued)