STI S.r.l. – Via Dei Caravaggi 15, 24040 Levate (BG) – ITALY www.imi-critical.com
Manual 5020, rev.03 07/2021 - SC/VHS 20
8.2.2 Fail retract version (FR)
Before dismounting the cylinder remove the actuator
from the valve or the valve coupling joint (see
paragraph 2.2)
8.2.2.1 Replacement of piston seals (Fig. 7.2)
Remove the nuts (21) fixing the piston (19) to the end
flange of the spring cartridge (8). Remove the piston
(19).
Remove the external seal (12) and piston seal (1).
Remove the sliding ring (14). Clean and lubricate all the
seal grooves and then mount the new seals and sliding
ring.
Before the final reassembling clean and lubricate all
surfaces in contact with seals.
Reinstall the seal (12) and then reassemble the piston
(19) fixing it on the end flange of the spring cartridge with
the screws (21).
8.2.2.2 Replacement of piston rod seal (Fig. 7.2)
Before to replace the piston rod seal (3) it is mandatory that the piston has been completely
reassembled, as per previous instruction 8.2.2.1.
The piston rod must be then moved a few mm using an hydraulic pump or similar device connected
to the piston entry to pressurize the cylinder.
Remove the holding ring (24) and retaining rings (23) and then remove the spring holding flange (13).
Remove the seal (3). Clean and lubricate the seal groove and mount the new seal. Reassemble the
spring holding flange (13) fixing it with retaining rings (23) and holding ring (24).
Release the pressure on the cylinder.
8.2.2.3 Replacement of stopper protection seals (when provided)
Remove travel stop protection (22) and replace the seal (22a) if necessary.
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