10
EB 8039 EN
Maintenance
7
Maintenance
See Fig. 1.
The on/off valve is subject to normal wear,
especially at the seat and plug. Depending
on the operating conditions, check the valve
at regular intervals to prevent possible fail-
ure before it can occur.
We recommend removing the parts, cleaning
them, and, if necessary, replacing them with
new ones.
Before starting any work on the valve body,
disconnect and remove the control pressure
line as well as the actuator.
WARNING!
Valves are not free of cavities. In par
-
ticular, residual process medium
might still be contained in the valve
version with bellows seal.
Process medium can escape uncon-
trolled on dismantling the valve.
Depressurize and drain the valve be-
fore removing it from the pipeline.
When used at high temperatures, al-
low the plant section to cool down to
ambient temperature.
External leakage can indicate that the dia-
phragm (5.4) and, in the special version, the
PTFE V-ring packing (4.2) are defective.
If the valve does not close tightly, tight shut-
off may be impaired by dirt stuck between
the seat (2) and plug (3) or by damaged fac
-
ings.
The procedures to disassemble the fail-close
and fail-open valve are not the same as the
plug is located differently in the valves.
A mounting device (see Fig. 2 and Table 2)
is needed as the spring (5.5) in the actuator
is preloaded.
To take out the seat ring, a special seat tool
(Table 2) is necessary.
Refer to Table 3 for the required tightening
torques.
7.1
Disassembly (DN 15 to 80)
1. Remove nuts and bolts at the actuator.
For versions with handwheel, turn the
handwheel to ensure that the spring plate
(5.6) is not under tension. Remove the di
-
aphragm case (5.7) and take out the di
-
aphragm.
2.
Place shim (around 5 mm thick) accord
-
ing to Fig. 1 on the spring plate. Place
on mounting device and fasten with three
clamping bolts and nuts. Turn the nuts
until the spring plate (5.6) is evenly load
-
ed slightly. This causes the plug (3) to de
-
tach itself from the seat.
3. Completely undo the threaded bushing
(5.2). Spray the lock nut (3.2) stuck with
adhesive to the plug stem as well as the
ends of the plug stem with solvent. Use a
hot-air gun to soften the adhesive and
undo the lock nut (3.2). Position plug
wrench (see Table 2) or hex screwdriver
(DN 65/80) and carefully turn the plug
stem clockwise until its height has
changed by approx. 6 mm.
Summary of Contents for 3351
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