ARI Armaturen STEVI 451 EN - 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