3.3: Fluid Properties

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List the purposes of fluid in a fluid power system

Define lubricity and the factors that influence lubricity

Describe why petroleum based oil is the liquid of choice for most hydraulic systems

Comment on the observed compressibility of liquids under pressure.

Define density.

Define specific weight, differentiate between it and density. Look up the specific weight of oil, water, and other common substances.

Define specific gravity. Look up the specific gravity of oil and other common substances.

Name the tool used to measure specific gravity of a liquid. Describe why a discharged battery has an SG reading closer to 1. Comment on properties that influence density, specific weight, and specific gravity.

Define viscosity.

Describe how viscosity is measured using a Saybolt viscometer.

Comment on the viscosity measurement of a thick fluid using units of SSU. Comment on the viscosity measurement of a thin fluid using units of SSU. Look up the viscosity of common liquids.

Comment on the advantages and disadvantages of liquids with high viscosity measurements.

Comment on the advantages and disadvantages of liquids with low viscosity measurements.

List another common viscosity unit.

Define viscosity index (VI). Comment on how temperature ordinarily affects viscosity. Comment on VI for liquids exhibiting excellent and poor viscosity stability.

Comment on manufacturers specifying viscosity measurements for data sheets.

Define pour point. Comment on the magnitude of a liquid’s pour point an application that must work in an extremely cold environment.

List common additives in a hydraulic system.
Comment on additive compatibility