Abstract: A straight travelling apparatus for heavy construction equipment, equipped with a travel supplement circuit, including a variable orifice disposed in a fluid line connected to the supply-side of the control valve of a bucket and controlled to vary an opening degree thereof by a predetermined pilot signal that is applied to the variable orifice in response to an operation of at least one of right and left travel motors in order to keep the variable orifice at a relatively closed state while being released in response to the travel motors not operating in order to keep the variable orifice in a relatively opened state, thereby capable of supplementing a sufficient amount of fluid to a travelling system when the bucket is operated during, thereby preventing an abrupt reduction in travelling speed caused by operatings the straight travelling apparatus.

Abstract: A motor cavitation prevention device for hydraulic systems is disclosed. The device exerts no influence upon return fluid of any actuators other than the hydraulic motor thereby preventing undesired pressure loss of the return line. The device has valve means installed in a given position of the return line such that the return fluid of the motor necessarily passes the check valve prior to returning to a return tank but the return fluid of the other actuators does not pass the check valve, and a feedback line for feeding the return fluid of the motor back to the motor in the ease of generation of the pressure above tank in the return line, one end of which feedback line is connected to the return line at the front of the check valve but the other end of which feedback line is connected to the motor.