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GB50-IOM Rev. 0 8/20
THIS INFORMATION IS SUBJECT TO THE CONTROLS OF THE EXPORT ADMINISTRATION REGULATIONS (EAR). THIS INFORMATION SHALL NOT BE PROVIDED TO
NON-US PERSONS OR TRANSFERRED BY ANY MEANS TO ANY LOCATION OUTSIDE THE UNITED STATES CONTRARY TO THE REQUIREMENTS OF THE EAR.
RANGE CHANGES
Standard range is 3-15 PSI (21-103 kPa). Other ranges
are available, consult the factory.
MATERIALS OF CONSTRUCTION
Cylinder Aluminum
Piston Aluminum
Stem
303 Stainless Steel
Seals Buna-N
Spacer Bars
Steel (when required)
Yoke
Ductile Iron (when required)
Model Number
Piston Diameters
GB50
3” (76 mm)
GB51
4” (102 mm)
GB52
6” (203 mm)
GB53
8” (203 mm)
MAINTENANCE
POSITIONER / ACCESSORIES
The positioner requires a minimum of maintenance. If
positioner or accessory servicing or replacements are
necessary, refer to the appropriate instructions and parts
list booklets.
PISTON ACTUATOR
The service life of the seals is such that replacement will
seldom be necessary under normal operating conditions.
Should disassembly become necessary, the following
procedure must be followed. The piston should be in the
“up” position. Disconnect tubing and bleed air out of the
unit.
Remove the cap from the positioner and the
Spirolox type retaining ring, directly under the cap, so
that the positioner head plate can be lifted out. Loosen
the set screw and remove the spring rod nut. Then
remove the six cap screws around the positioner flange
and lift the positioner from the head plate.
GB50:
Remove the set screws and lift out the cylinder
head plate.
GB51/55:
Remove the cover, Spirolox type retaining ring,
and lift out the cylinder head plate.
Disconnect the actuator stem from the unit being
serviced. Slide out the piston and actuator stem nut
assembly. The piston seal(s) may now be inspected.
Any water, dirt, or sludge which may have accumulated
inside the cylinder should be removed. The stem o-ring
should be replaced each time by removing the retaining
ring (Tru-Arc ring) and retaining plate.
Before reassembling, apply a thin layer of grease (Dow-
Corning #DC-33 light lubricant or equivalent) to the inner
wall of the cylinder, actuator stem, piston seal(s) and the
seal groove(s) in the piston. Care should be exercised
when inserting the piston into the cylinder because the
seal is designed for some interference with the cylinder
bore and must pass over a small step to enter the
cylinder bore.
If the piston will not enter the cylinder bore, run a shim
(approximately .010” thick x 1/2” wide) between the seal(s)
and cylinder wall while applying slight pressure to the
piston.
The stem must be carefully guided and inserted through
the bearing to prevent damage of the bearing surface by
the thread of the stem.
PISTON ACTUATOR SERVICE KITS
Standard spare parts kits are available that contain all
the seals required to service GB50-GB53 size cylinders.
These kits contain both types of piston seals (lip seals
and quad rings), as well as replacement o-rings for the
stem seal and the head plate seal.
Actuator Model
Spare Parts Kit
GB50
G6385343
GB51
G6385344
GB52
G6385345
GB53
G6385346
