The invention discloses a rotary energy saving
system of an
excavator. When the
excavator rotates to be started, corresponding flow is supplied according to a demand of a rotary motor, so that overflow loss of the
system is reduced. A flow control valve is arranged between an overload buffering valve and an
oil tank. In a process of accelerating rotary starting, the flow control valve works in a throttling mode; flow, namely overflow of the
system, of the flow control valve is calculated according to pressure at an oil inlet of the flow control valve, and the
discharge capacity of a
hydraulic pump is adjusted according to the overflow of the system; when the overflow is increased, the
discharge capacity of the
hydraulic pump is reduced, so that most of the pump output flow is absorbed by the rotary motor, and
energy loss is reduced; when the overflow is reduced, the
discharge cavity of the
hydraulic pump is improved, so that the requirement of the rotary motor can be met; moreover, the
inlet pressure of the rotary motor is always kept at an overflow pressure value, and the rotary torque is increased, so that the rotary acceleration performance is guaranteed; and in a process of rotary deceleration
brake, the flow control valve works in a direct through mode, so that
oil can be normally filled into the rotary motor.