Page 83 - Fluid Power Engineering

60 Cha pte r T h ree

• Material of tubing
• Fittings
• Tubing size
• Tubing length
• Conveyed fluid compatibility
• Temperature
• Tubing pressure rating
• Installation design

High-pressure hydraulic tubes are mostly produced from carbon
steel. Manufacturers make a wide range of tube dimensions and wall
thicknesses to work with a wide range of flow rates and pressures.
Table 3.1 gives typical parameters of commonly used tubes.
The proper tube diameter is determined according to the maxi-
mum flow rate and selected fluid speed.

4 Q
d = max (3.1)
π v

where d = Tube inner diameter, m
3
Q = Maximum flow rate, m /s
max
v = Fluid mean velocity, m/s
The recommended mean fluid velocity in rigid pipes is usually
within 2 to 6 m/s for the pressure line and 0.6 to 1.6 m/s for the suc-
tion, return, and low pressure lines. The inner diameter of a tube can
also be calculated by using the nomogram given in Fig. 3.1, while the
pipe wall thickness is determined according to the operating pres-
sure, shown in Table 3.1.
The selection of the proper tube fittings and connectors is essential
for the correct operation as well as the safe use of tubing and related
equipment. Improper selection of the fittings can result in tube leak-
age, bursting, and other failures. Figures 3.2 and 3.3 give typical tube
end fittings and connectors.
The proper installation of the tubing is essential to the correct opera-
tion and safe use of the tubing. The following comments should be con-
sidered for the mounting of hydraulic tubes, as illustrated by Fig. 3.4:
• Tubing should be bent wherever possible to reduce the number
of fittings, and should be bent using proper tube bending
equipment (as shown in images 1, 2, and 3 of Fig. 3.4).
• The symmetrical design of piping systems makes them easier
to install and present a neat appearance (as shown in image 1).