Codes: Hydraulic System Components and Fluids Flashcards
What are some characteristics must be considered when selecting a hydraulic fluid?
Viscosity, chemical stability, flash point, and fire point.
What is viscosity?
Viscosity is internal resistance to flow and is one of the most important properties of any hydraulic fluid.
As temperature decreases, viscosity…
increases.
A satisfactory liquid for a given hydraulic system must have enough body to give a good seal at pumps, valves, and pistons, but it must not be so thick that it offers resistance to flow, leading to power loss and higher operating temperatures.
Ain’t that cool?
What tool measures viscosity?
A viscometer.
What is chemical stability?
A liquids ability to resist oxidation and deterioration for long periods.
Why does the temperatures of the liquid in the reservoir of an operating hydraulic system not always represent a true state of operating conditions?
Because localized hot spots occur on bearings, gear teeth, or at the point where liquid under pressure is forced through a small orifice. The passage of a liquid through these points may produce local temperatures high enough to carbonize or sludge the liquid, yet the liquid in the reservoir may not indicate an excessively high temperature.
What conditions can cause a hydraulic liquid to break down?
Exposure to air, water, salt, or other impurities, or contact with some metals such as zinc, lead, brass, and copper.
What negative effects will occur when a hydraulic liquid that has been subjected to unfavorable conditions?
It will become darker in color, higher in viscosity, and acids will form.
What is flash point?
the temperature at which a liquid gives off vapor in sufficient quantity to ignite momentarily or flash when a flame is applied.
What is fire point?
The temperature at which a substance gives off vapor in sufficient quantity to ignite and continue to burn when exposed to a spark or flame.
How does a mechanic know what type of hydraulic fluid to use?
Use the type listed in the maintenance manual or on the instruction plate affixed to the reservoir.
What are the three principal categories of hydraulic fluids?
Minerals
Polyalphaolefins
Phosphate esters.
Describe MIL-H-5606
Mineral based, processed from petroleum, odor similar to penetrating oil, dyed red. Used when the fire hazard is comparatively low.
Describe MIL-H-83282
Polyalphaolefin, fire resistant, developed to overcome flammability of 5606, high viscosity at low temps. generally limited to -40 degrees Fahrenheit.
