Specifications
GOLDCUP CONTROLS SERIES 400
CODE 4B*/4C* ROTARY SERVO
SPRING CENTERED WITH
TRIMMER, BRAKE AND
BYPASS VALVE
S23-12343 (4B*)
S23-12324 (4C*)
DESCRIPTION
DISASSEMBLY
See Figure 4C
PREPARATION FOR ASSEMBLY
REWORK OF WEAR PARTS
Code 4B* and 4C* cross center pump controls are spring and pressure centered and
can be manually stroked to full displacement either side of center with approximately
20 lbs-in. (2.26 Nm) torque. The centered position may be adjusted externally to
approximately +/- 5% displacement. In the 4C control, maximum stops may be adjust-
ed from full to zero displacement.
In the same body is contained the brake and bypass valve option. A brake spool,
when energized, connects the brake port to servo pressure. When de-energized, a
spring shifts the spool, connecting the brake port to tank. Another port, located on the
end of the brake valve, is closed by the energizing of the brake spool. When de-ener-
gized, this port dumps both pump system ports to the replenishing source, thus
bypassing the small flow generated by slight errors on zero position.
The operation is controlled in this manner: A restricted servo flow is applied to shift
the brake spool. This flow is dumped when a slot in the servo plate aligns with a pas-
sage connecting to this spool. This occurs when the pump is on zero stroke. Another
restricted flow is applied to a spool adjacent to the brake spool. This flow is also con-
nected to a passage in one centering piston, containing a ball and seat. When the
control is off center, the ball seats, sealing the passage, to apply servo pressure to the
spool. When the control is on center, a pin extending from the other centering piston
pushes the ball off the seat, to dump the flow,
The brake spool is thus de-energized to set the brake when BOTH the pump cam is at
zero stroke and the rotary servo is at zero command. If the pump is on stroke or the
input is on stroke, the brake spool is energized, releasing the brake.
1. Disconnect brake and bypass lines from control. Remove screws (2). Remove con-
trol from pump. Examine servo plate for excessive scratching. Note if orifices in stem
are open. If servo plate is scratched or orifices appear to be plugged, remove plate
and servo stem by removing two socket setscrews from plate, then alternately loosen-
ing the two button head screws under the set screws.
2. Remove retaining ring (4) and press the shaft assembly through the valve body.
3. Examine shoes (8) and (50) for contamination in balance pads or excessive
scratching on faces. Note: the two shoes are not identical and must be installed in the
proper position on reassembly.
4. Remove plugs (28) with attached parts. Remove springs (27), pistons (26), and
spools (22), with attached parts. Do not disassemble unless parts are damaged.
Examine spools, pistons and bores for free motion, wear or contamination.
5. If trimmer adjustment must be removed, carefully tap the spring pin (17) in till flush
with O.D. of screw (16). Remove nut (18), and screw (16). Remove spring pin (17)
from screw.
6. Remove bypass valve body (39) with fitting (41) piston (42) and spring (37).
Remove plug (35) and spring (34). Remove spools (33) and (36).
7. Remove shoe (48), and spring (47).
8. Blow through passages to check two orifices (11) and orifice (10) in body for conta-
mination. Check passages in body for free flow.
All parts are to be inspected and be free of material defects, dirt, scratches or any for-
eign material.
All parts are to be cleaned with a suitable cleaning solvent and all cores and passages
blown out with clean dry compressed air.
After cleaning and inspection, all parts are to be covered with a light film of oil and
should be protected from dirt and excessive handling until assembled onto the unit.
During assembly, lapped and ground surfaces should be kept lubricated and protected
from nicks or surface damage.
22
Description Rework
Servo plate face Fine stone to remove raised burrs & dings
Shear seal Fine stone to remove raised burrs & dings. Note:
grooves to supply balance pads must be present
and adequate.
Control cover Stone or lap inside face to remove raised burrs &
dings.
Spool Break sharp edges or dings.