A
pipe layer having a swing speed adjustable
system is provided, which can be used as a
pipe layer or an
excavator through replacement of attachments in accordance with work conditions, so that it serves as the
pipe layer when it is required to
pull up and carry a heavyweight oil pipe in order to lay the oil pipe under the ground, while it serves as the
excavator when a quick swing work is required. The
pipe layer having a swing speed adjustable
system includes first and second
variable displacement hydraulic pumps connected to an engine,
control valves installed in a center bypass path of the first
hydraulic pump,
control valves installed in a center bypass path of the second
hydraulic pump, a straight traveling valve installed on an upstream side of the center bypass passage of the first
hydraulic pump to supply the
hydraulic fluid from the first and second hydraulic pumps to a boom cylinder, a swing motor, a
winch motor, and left and right traveling motors, respectively, and a
variable load-hold
check valve installed in an inlet-side flow path of the swing
motor control valve to variably adjust a
stroke of a poppet so that the amount of
hydraulic fluid being supplied to the swing motor can be variably adjusted.