to its function within the system. In general, hydraulic
lines are designated as follows:
SUPPLY LINES—These lines carry fluid from the
reservoir to the pumps. They may be called suction
lines.
PRESSURE LINES—These lines carry only pres-
sure. They lead from the pumps to a pressure manifold,
and from the pressure manifold to the various selector
valves. Or, they may lead directly from the pump to the
selector valve.
OPERATING LINES—These lines alternately
carry pressure to, and return fluid from, an actuating
unit. They also may be called working lines. Each line
is identified according to its specific function.
RETURN LINES—These lines return fluid from
any portion of the system to a reservoir.
VENT LINES—These lines carry excess fluid
overboard or into another receptacle.
MIL-STD-17B, part II, lists symbols that are used
on hydraulic diagrams. Figure 5-16 shows the basic
outline of each symbol. In the actual hydraulic
diagrams the basic symbols are often improved,
showing a cutaway section of the unit.
Figure 5-16.—Basic types of hydraulic symbols.
5-12
