Koso REXA Electraulic Xpac, Installation And Operation Manual

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REXA
Electraulic Actuators & Drives
Xpac
Installation Manual -- Version 5.1 (5/08)
F-3
F. SEAT LOADING CYLINDER
Linear actuators which must come up against a hard stop (valve
seat) use a spring loaded element between the actuator and valve
stems. This elastic coupling provides a controlled loading of the
seat without over stressing mating parts. Its purpose is the same as
torque limit switches found on gear motor actuators, but without the
inherent adjustment difficulties and potential for faulty calibration.
On larger size units (thrusts of 40,000 lbs or greater), the forces are
too large to use a mechanical elastic coupling. Instead, a smaller
Seat Loading Cylinder (SLC) with an extend spring applying force
to its shaft is hydraulically connected to the main cylinder. The
spring is precompressed to a load equivalent to 80% of the nominal
working pressure. Hydraulic fluid will not begin entering the SLC
until the pressure in the main cylinder rises above this value. This
will typically only occur on the valve seat. As the pressure builds
within the cylinders, oil flows into the SLC and retracts the shaft.
When the spring is compressed to the full nominal working pres-
sure, the power module will shut off. The rated actuator output is
now applied to the driven device and retained within the cylinders
by the Flow Matching Valves.
F.1 Mechanical Installation
The Seat Loading Cylinder is mounted to the side of the main cyl-
inder at the factory. All hydraulic piping and spring preload will be
complete. Mechanical installation is not required.
F.2 Electrical Installation
Operation of the Seat Loading Cylinder requires the connection of
a feedback cable between the SLC and the control enclosure. The
standard cable consists of a red, white and black wire and a tinned
copper ground wire. Each individual wire is 18 AWG. The feedback
cable is not restricted by distance.
F.2.1 Enclosure Termination
The red wire, +15 VDC, and black wire, Feedback (-), are connected
to the same terminals as for the main cylinder feedback cable. These
wiring instructions can be found in Section 5.2 for the C or 2C Power
Modules or Appendix X 2.3.1 for the D or 2D Power Modules. The
white wire, Feedback (+), is connected to a screw terminal, P3-6,
marked as “SLC Feedback (+).
The feedback cable of the Seat Load-
ing Cylinder is in addition to the feed-
back cable for the main cylinder (Sec-
tion 5.2). The two feedback cables
may be run within the same conduit.