Trinity Highway INGAL SS180 M, Assembly Manual

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trinityhighway.com 29 Revision A November 2019
Hydraulic Fluid
1. Purpose
The main purpose of hydraulic fluid is to transfer power from the pump to the actuators.
Secondary tasks include reducing metal on metal friction and preventing the formation of
rust and sludge. These traits are achieved when the oil has a good lubricity (slipperiness),
and with additives that inhibit oxidation and the entrainment of air and water in the oil,
respectively. The viscosity (thickness) of the oil must be appropriate for the operating
temperature to minimize unwanted leakage and to lubricate the close fitting parts in the
system.
Additionally, the oil must be compatible with the seals used in the system. Finally, the oil
must be able to pour or
fl
ow at the lowest expected operating temperature so that it can
enter the reservoir and pump for use. For all of these reasons, automatic transmission
fl
uid (ATF, Dexron
TM
III) has been found to be the best readily available
fl
uid for the job in
most climate conditions.
2. Selecting Fluids for Applications Outside ATF’S Temperature Range
When looking for fluids that can be used in place of ATF or for applications where the
operating temperature is outside the range of ATF, the following specs should be discussed
with your local oil distributor:
A. Fluid must be compatible with Buna-N sealing compounds.
B. The pour point of fluid used must be below the lowest anticipated temperature.
C. Fluid should contain Rust or Oxidation inhibitors as well as other detergent type
inhibitors.
D. Fluid viscosity (SUS) must have an operating range between 80 and 375, with the ideal
viscosity near 200 SUS.
E. The viscosity index should be as high as possible. As an example, ATF has the
following specs listed for most oil manufacturers:
[1] Viscosity (SUS)
37 º C
99 º C
Pour Point
185 to 205
45 to 55
-47 º F [-44º C] to
-35 º F [-37º C]
Viscosity Index
145 to 165