STI S.r.l. – Via Dei Caravaggi 15, 24040 Levate (BG) – ITALY www.imi-critical.com
Manual 5020, rev.03 07/2021 - SC/VHS 19
8.2 Special maintenance
Under normal condition the actuator doesn’t need special maintenance.
If there are leaks in the hydraulic cylinder or a malfunction in the mechanical components, or in case
of scheduled preventive maintenance, the actuator must be disassembled and seals or any other
defective parts must be replaced.
Replacement of seals must be done with reference to the attached sectional drawing and adopting
the relevant procedures.
8.2.1 Fail extend version (FE)
Before dismounting the cylinder remove the actuator
from the valve or the valve coupling joint.
(see paragraph 2.2)
8.2.1.1 Replacement of piston seals (Fig. 7.1)
Remove the nuts (21) fixing the head flange (19) to the
spring cartridge (8). Remove the head flange (19).
Remove all the external (1), (2) and internal (3) seals
form piston/head flange. Remove the sliding ring (14).
Remove the seal (13) between the head flange and
spring cartridge. Clean and lubricate all the seal grooves
and then mount the new seals and sliding ring.
8.2.1.2 Replacement of piston rod seal (Fig.
7.1)
Remove the cylinder tube (7) from the spring cartridge.
Unscrew completely the nut (9) allowing the piston rod
(17) to be removed from the cylinder tube; remove now
the seal (12) and the back-up ring (5). Clean and
lubricate all the seal groove and mount the new seal and
back-up ring; reassemble then the tie rod.
8.2.1.3 Final reassembling (Fig. 7.1)
Before the final reassembling clean and lubricate all surfaces in contact with seals.
Reassemble the piston tube (7) and piston/head flange (19) fixing the assembly on the spring
cartridge with the screws (21).
8.2.1.4 Replacement of stopper protection seals (when provided)
Remove travel stop protection (22) and replace the seal (22a) if necessary.
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