Koso REXA Electraulic Xpac, Installation And Operation Manual

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REXA
Electraulic Actuators & Drives
Xpac
Installation Manual -- Version 5.1 (5/08)
43
In general, the REXA power modules will develop their nominal pres-
sure (2000 PSI) over a wide range of temperatures (0° to 160° F) and
speed settings (40% to 100%). It is only in the extreme where output
drops below the ratings. Depending on the situation,
REXA has avail-
able different remedies to insure adequate viscosity of the oil and thus
insure nominal pump pressure.
7.5.1 Fail In Place Actuators
Fail in place actuators have the full output ratings available in both
directions of motion.
7.5.2 Spring Return Actuators
Spring return actuators have the rated output minus the spring load
available in the direction opposing the spring and the rated output plus
spring load in the direction of the spring load. Upon power failure only
the spring load is available. The spring range should be indicated on
the specification. See TM4,
Spring Failure , for details.
7.6 Temperature
Oil is used as the means to transfer rotary motion of the motor into
mechanical thrust or torque. Because oil is essentially incompressible
REXA actuators exhibit high stiffness and therefore can precisely posi-
tion large loads. The viscosity of the oil is essential to the operation of
the actuator. If the oil is heated the viscosity decreases until at some
elevated temperature the thickness becomes too low for the gear pump
to produce the necessary output pressure. Conversely if the oil is cooled,
the viscosity increases until the torque required to pump the thickened
oil stalls the motor. For this reason the specific oil used is temperature
range dependent.
The chart (next page) shows the temperature ranges for the recommended
automotive oil (Castrol Syntec SAE 5W-50). This is for a speed setting
between 80% and 100%. A speed setting below 80% may allow opera-
tion at somewhat lower temperatures than specified. Three ranges are
identified:
TR 1:
The standard oil and the cartridge heater;
TR 2:
One inch of thermal insulation covering the entire unit is recom-
mended;
TR 3:
Heat tracing should be provided in conjunction with a one inch
covering of thermal insulation.
For electrical power sensitive installations, the cartridge heater is not
required for the standard oil at ambient temperatures above 25°F.