Flowserve Edward Cast Steel Bolted Bonnet Valves - Manual (Page 6)

6
Flow Control Division
Edward Valves
Service Problems
(cont.)
line at that point is sufficiently warm to
keep the insulation 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, by corrosion, by flakes of line scale,
or by particles of weld spatter that may
have entered the valve during construction
of the piping, and which later washed up
into the piston bearing area of the
body I.D.
The stem of a stop-check valve should
normally be fully open 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, bonnet and handwheel. Screwing
the stem down slowly to contact the disk
first increases the intensity of vibration to
the hand and to the ear, but further down-
ward movement of the stem builds up suffi-
cient contact pressure and eliminates the
vibration. This also tends to dislodge any
foreign particles which may have been the
initial cause for disk-piston wedging.
The position of the stem where vibration
ceased, should be noted and any increase
in pressure drop indicated on available
gages, recorded. It may be that when the
stem is screwed back to the full open posi-
tion, the disk will again remain in a float-
ing position which could indicate oversiz-
ing of the valve for the flow conditions. It is
always recommended that check valve size
selection be governed by flow conditions
rather than by adjacent piping. Oversizing
induces vibration or noise and causes
excessive, uneven guide rib wear giving
rise to greater disk-piston assembly clear-
ance on one side of the body.
Another way to dislodge a wedged piston
is to use other valves in the line. If possi-
ble, 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.
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 actuator, the
bearings are lubricated by the actuator
lube supply, which should by maintained
at the recommended level.
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 is 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 re-lube schedule.
For valves that are operated infrequently,
relubrication at least once a year is recom-
mended. The recommended lubricant for
stem threads is Rykon EP #2, manufactured
by The American Oil Company. This is an
extreme pressure, extreme temperature
lubricant of high quality.