0 troubleshooting table – ARI Armaturen STEVI 451 EN User Manual
Page 20

Page 20
Rev. 0040306000 0410
Operating and installation instructions
3-way control valves - STEVI
®
450 / 451
9.0 Troubleshooting table
ATTENTION !
- read item 10.0 and 11.0 prior to dismantling and repair work!
- read item 6.0 before restarting the plant !
Fault
Possible cause
Corrective measures
No flow
Valve closed
Open valve (using actuator)
Flange covers not removed
Remove flange covers
Little flow
Valve not sufficiently open
Open valve (using actuator)
Dirt sieve clogged
Clean / replace sieve
Piping system clogged
Check piping system
Kvs value of valve unsuitable
Fit valve with higher Kvs value
Stem moves in jerks.
Stuffing box sealing too tight
(for valves with graphite packings)
Slacken screw joint (pos. 42/20.17) or
hexagon nuts (pos. 24) slightly;
valve must not start leaking!
Valve plug slightly seized owing to solid
dirt particles
Clean internals, smooth rough spots.
Stem or plug cannot be
moved.
Seatring and plug clogged with dirt;
especially with V-port and perforated
plugs
Clean seatring and plug with suitable
solvent
Valve plug seized in seatring or guide
owing to deposits or dirt in medium
Replace plug and seatring; use parts
made from different material if neces-
sary
Stem leaking.
PTFE V-ring unit damaged or worn
Replace ring pack; refer to item 7.2
In valves with packed stuffing boxes
tighten screw joint (pos. 42)
Tighten screw joint (pos. 42) or hex.
nuts (pos. 24); replace packing if nec-
essary; refer to item 7.1.2
Bellows defective in valves with bellow
seal
Replace bellows unit; refer to item
7.1.3
Leakage too high when
valve is closed.
Sealing surfaces of plug eroded or worn Replace plug; refer to item 7.2
Sealing edge of seatring damages or
worn
Replace seatring; refer to item 7.2
Seatring and/or plug dirty.
Clean internal parts of the valve
Pneumatic actuator not completely
vented; spring force not fully effective
Vent actuator air chamber completely
Actuator not powerful enough
Install more powerful actuator;
check service data
Stem “hammers”.
flow in the closing direction
Compare the plug operation (mixing- or
diverting plug) with the application and
if necessary exchange the fittings or
increase actuator force