Instruction Manual
D104483X012
785C Actuator
May 2022
27
Assembling the Pneumatic Cylinder
The cylinder is reassembled by following in reverse order the sequence described in section Disassembling the
Pneumatic Cylinder. The screws must be tightened properly. Refer to table 10.
If only a partial replacement of the pneumatic cylinder seals has been performed, the pneumatic cylinder assembly
procedure starts from step 3.
1. Ensure the seals (key 2102, 2107 and 2202) of the head flange (key 2201) have been replaced, lubricated, and are
properly seated.
2. Install the head flange (key 2201) on to the spring cylinder (in case of 785C spring return actuator) or on to the yoke
(in case of 785C springless actuator).
3. Place the washers (key 2106).
4. Lubricate bolts (key 2105) and torque to values given in table 10.
5. Ensure the seal (key 2204) of the head flange (key 2201) is replaced, lubricated, and properly seated.
6. Place the washer (key 2205) on the stem. Thread the piston (key 2206) on to the stem. Rotate clockwise until it
seats on the piston then turn another 1/4 turn
.
7. Ensure the seal and gasket (key 2207 and 2208) of the piston (key 2206) are replaced and properly seated. Make
sure the seal is well lubricated.
8. Lift the cylinder (key 2209) and put it back in place by performing the operations below:
a. Thoroughly clean the cylinder (key 2209) inner surface and ensure the surface nor the chamfers are damaged.
b. Lubricate the entire inner surface and chamfers.
c. Slide the cylinder (key 2209) onto the piston taking care not to damage the cylinder inner surface, piston seal
(key 2208), gasket (key 2207) and the head flange seal (key 2204).
d. The full mating surface of the cylinder (key 2209) should rest against the head flange (key 2201)
.
The cylinder
(key 2209) is not provided with screw interfaces for handling purposes. Use padded clamps or jaws to prevent
damaging.
9. Ensure the seal (key 2204) of the top end flange (key 2210) is replaced and properly seated.
10. Assemble the end flange (key 2210) by centering it with the inside diameter of the cylinder (key 2209), taking care
not to damage the seal (key 2204). The full surface of the end flange should rest against the mating cylinder
(key 2209) face
.
Align the top and bottom end flange (key 2210) tie rod holes.
11. Screw each tie rod (key 2213) back in its housing on the head flange.
12. Install the washers (key 2211) and tighten the nuts (key 2212) on the tie rods (key 2213) in a crisscross pattern to
the appropriate torque per table 10.
13. Refer to the Actuator Mounting section of this manual for instructions on mounting and reinstalling the actuator
onto the valve. As best practice, check for leakage after installation for all sealing surfaces
.