The hydraulic system consists of an oil sump, one or two oil pumps, an air over oil accumulator tank, and piping to the servomotors. Typically, there are two pumps with lead and lag controls so that there is always a backup pump. Some systems will share two pumps between two units so that in an emergency one pump could be used for both units. The accumulator tank is usually sized so that in the event the pumps fail, the gates can still be closed. The size of the valve required to control the large amount of oil.
