The invention discloses a position compensation extendable-and-retractable type boarding trestle hydraulic
system. The position compensation extendable-and-retractable type boarding trestle hydraulicsystem comprises a power
system, a rotation hydraulic
system, an extending-and-retracting hydraulic system and variable amplitude hydraulic systems. The power system comprises a hydraulic
oil tank, main pump sets and a high-low pressure pump set. The rotation hydraulic system comprises a rotation selection valve, a direction and speed control valve, a
brake control valve, a
mode selection valve, afirst balance valve, a second balance valve, a two-way direction valve, a sequence valve, a
hydraulic motor and brakes. The extending-and-retracting hydraulic system comprises an extending-and-retracting selection valve, a direction and speed control valve, a
brake control valve, a
mode selection valve, a first balance valve, a second balance valve, a two-way direction valve, a sequence valve, ahydraulic motor and an extending-and-retracting
brake. Each variable amplitude hydraulic system comprises a variable amplitude selection valve, a variable amplitude direction and speed control valve,a variable amplitude energy accumulator control valve, a variable amplitude energy accumulator switch valve, a variable amplitude energy accumulator oil charging control valve, a
plunger type energy accumulator and a variable amplitude oil cylinder. By means of the system, manual overlapping,
active compensation and
servo compensation can be achieved, and footbridges can be overlapped reliably andsafely.