THD SERIES S09 HEAVY DUTY ACTUATORS
Installation & Maintenance Manual
documents\products\IOM\IOM8037
8. Replacement of Cylinder Seals
When the cylinder seals must be replaced, because of
leakage or a preventive scheduled maintenance, the
following procedure must be followed. Note only the soft
parts indicated on page 5 are included in a seal kit. If
additional parts are required they must be ordered
separately.
Due to the continuing improvement of the Heavy Duty
Actuators, seal kits provided by A-T Controls may contain
extra o-rings so that all revisions of the actuators are able to
be repaired. When disassembling the actuator, it is
recommended to match the old o-ring with the new o-ring
from the repair kit by comparing the o-ring diameter and
cross section.
1. Disconnect electrical supplies and shut off pneumatic
supply, vent actuator and remove from valve or damper.
2. For spring return actuators the spring tension must be
relieved before starting. Apply air pressure until the
piston moves off the stop bolt. Loosen the hex nut (item
12) then back out the stop bolt (item 11) until the preload
is relieved. For double acting units the actuator should be
in the clockwise position with the piston next to the rear
flange.
3. Vent all air pressure from the cylinder (item 14).
4. Attach a lifting device to the lifting hook on the spring
cylinder and remove the 4 bolts on the spring cartridge.
Then carefully slide the spring cartridge off the piston rod
not to lose the thrust bearing on the end of the piston rod.
5. Remove the tie rod nuts (item 19) from the tie rods (item
23).
6. Remove the end cap (item 18) from the cylinder (item
14).
7. Remove the cylinder from the adapter (item 25) by
pulling over the piston (item 21). Use caution not to
scratch the cylinder bore when sliding over piston.
8. Bend the safety tab on the lock nut retainer up and out of
the groove. Remove the outer hex nut (item 20) holding
the piston on the piston rod (item 15). Then remove the
safety tab and then the inner nut.
9. Remove the piston (item 21), rod washer and o-ring (item
22).
10. Remove 2 each flat head screws in the adapter and
remove the cover plate.
11. Remove the o-ring seal assembly (item 24) from the
counter-bore.
12. Remove the o-rings from the piston and both flanges.
13. Clean all parts with a mild solvent that will not attack the
coating on the parts.
14. The center body assembly should be inspected before the
pressure group is rebuilt.
15. Remove the rod cover adapter (item 30).
16. Remove the pinion cover or any accessories mounted on
top of actuator. Remove snap ring on pinion and remove
upper pinion spacer and thrust washer. Slide pinion (item
2) down thru body and carefully remove from bottom of
actuator as not to damage the upper and lower bearings
and o-rings. Remove the piston rod and yoke assembly
thru the pressure port opening.
17. Inspect the Yoke pin bushing (bronze slider) (item 10) for
wear along with the slot in the yoke arm.
18. Inspect the upper and lower yoke bearings (item 4, 7) for
wear.
19. Wipe out old grease and replace with new grease on all
sliding surfaces.
20. Reinstall piston rod and yoke assembly into housing.
21. Then reinstall Pinion into yoke aligning the key into the
keyway and bearing careful not to harm the bearings or
the o-rings.
22. Reinstall the pinion thrust washer and snap ring washer
followed by the snap ring and pinion cover.
23. Lightly grease new o-ring rod seal assembly (item 26) and
install in front flange. Replace cover plate and install 2
each flat head socket cap screws.
24. Install adapter gasket on actuator using a gasket adhesive.
25. Reinstall adapter over piston rod and slide into position
and torque bolts in a diagonal pattern.
26. Install rod cover adapter gasket on actuator using a gasket
adhesive
27. Reinstall rod cover adapter and bushing over piston rod
and slide into position and torque bolts in a diagonal
pattern.
28. Lightly grease the o-ring for the front flange and install in
the groove.
29. Place piston rod washer on piston rod with countersink
facing out toward the end cap. Lightly grease o-ring (item
22) and slide over piston rod. Slide piston over piston rod
and install inner hex nut then lock tab and outer hex nut
then align outer hex nut with tab and bend into groove.
30. At this point the piston should be able to be pushed back
and forth to insure that all parts are in proper alignment
and working properly.
31. Lightly grease piston grooves and install o-ring and back-
up strip.
32. Lightly grease cylinder completely on the inside surface
and carefully slide over the piston until seated on the
adapter.
