ARI Armaturen STEVI 426 EN - Manual (Page 14)

Page 14 Rev. 0040314001 0410
Operating and installation instructions
Straight through control valves - STEVI
®
425 / 426
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.
Valve stem moves in jerks. Stuffing box sealing too tight (for valves
with graphite packings) Slacken stuffing box gland with nut
(pos. 18 resp. 20.29);
Valve must nor start leaking!
Valve plug slightly seized owing to
solid dirt particles Clean internals, smooth rough spots.
Valve stem or plug cannot be
moved. Seating and plug are clogged with dirt;
especially with V-port and perforated
plugs Clean seating and plug with suitable
solvent
Valve plug seized in seating or guide
owing to deposits or dirt in medium Replace plug and seating; use parts
made from different material if neces-
sary; refer to item 7.2
Valve stem leaking. Defective stem sealing in valves with
EPDM stem sealing Replace stem sealing;
refer to item 7.1.1
Stuffing box gland too slack in valves
with stuffing box packings Tighten stuffing box gland with nuts
(pos. 22) or repack; refer to item 7.1.2
Bellows defective in valves with bellow
seal Replace bellows unit (pos. 20.3);
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 seating damages or
worn Grind the seat resp. replace seat ring;
refer to item 7.2,
fit dirt sieve if necessary.
Piston sealing ring worn
(pressure-relieved valves) Replace sealing ring; refer to item
7.2.2
Seating and/or plug dirty Clean internals of valve; fit dirt sieve if
necessary
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