There are many types of valves, such as selector, pressure
reducing, sequence, check, restrictor, and relief. While the
basic function for each type of valve is similar, the design and
construction may be very different. Examples of these valves are
discussed in the following text. Selector valves are used in a
hydraulic system to direct the flow of fluid. A selector valve
directs fluid under system pressure to the desired working port
of an actuating unit (double-acting), and, at the same time,
directs return fluid from the opposite working port of the
actuating unit to the reservoir. Some aircraft maintenance
instruction manuals (MIMs) refer to selector valves as control
valves. It is true that selector valves may be placed in this
classification, but you should understand that all control
valves are not selector valves. In the strict sense of the term,
a selector valve is one that is engaged at the will of the pilot
or copilot for the purpose of directing fluid to the desired
actuating unit. This is not tr