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CHAPTER 3
Hydraulic
Transmission Lines
3.1 Introduction
Hydraulic power systems use hydraulic liquids to transmit hydrau-
lic power. The elements of the system are interconnected by hydrau-
lic transmission lines, through which the hydraulic liquid flows.
These lines are either rigid tubing or flexible hoses. The rigid
tubing lines connect fixed nonvibrating elements, and the flexible
hose lines connect moving parts. In addition, the coaxial joints are
employed to transfer liquid between the elements rotating relative to
each other.
Regardless of their simple design, the hydraulic conduits have
an important effect on the steady state and transient behavior of the
system.
Transmission lines affect system performance in the following
ways:
• Hydraulic friction losses; hydraulic resistance of lines
• Hydraulic local, or secondary, pressure losses
• Oil compressibility and elasticity of pipe material; hydraulic
capacitance of lines
• Oil inertia; the hydraulic inertia of lines
This chapter deals with the construction of tubes and hoses and
their fittings, as well as the static and dynamic performance of trans-
mission lines.
3.2 Hydraulic Tubing
The following are the basic factors involved in the selection of the
proper tubing:
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