Page 73 - Fluid Power Engineering

50 Cha pte r T w o

VG32 VG68
Density (at 15°C), kg/m 3 869 878
Pour point, °C −45 −36
Flash point, °C 212 252
Minimum startup temperature, °C −32 −21
Estimated operating range, °C −14 to 67 0 to 87

at 40°C 32.2 67.9
Kinematic viscosity, cSt
at 100°C 6.4 10
Viscosity index 156 132

TABLE 2.1 Specification of Typical All-Season Mineral-Based Hydraulic Oils

• Corrosion protection by adding effective corrosion inhibitors.
• Rapid de-aeration and air separation.
• Good thermal conductivity is required to rapidly dissipate
the heat generated due to friction between elements and due
to hydraulic losses.
• Fire resistance is essential in some applications.
• Electrically insulating properties can be significant in a
number of modern designs.
• Environmental acceptability.

Table 2.1 gives the specifications of two typical mineral-based
hydraulic liquids.

2.6 Exercises

1. Derive an expression for the pressure and power losses in a hydraulic
transmission line of constant diameter in the case of laminar flow.

2. Derive an expression for the hydraulic resistance, R, of a hydraulic
transmission line and find the resultant resistance of two lines connected in
series or in parallel.

3. Derive an expression for the hydraulic inertia of a transmission line.
4. Derive an expression for the hydraulic inertia of two hydraulic transmission
lines connected in series or in parallel.