to its function within the system. In general, hydraulic
lines are designated as follows:
SUPPLY LINESThese lines carry fluid from the
reservoir to the pumps. They may be called suction
PRESSURE LINESThese 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
OPERATING LINESThese 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 LINESThese lines return fluid from
any portion of the system to a reservoir.
VENT LINESThese 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.