Bucket rod throttle valve
The bucket operates next to the spool in the four-way change-over valve. When the boom and the bucket rod are operated at the same time, most of the pressure oil flows to the oil circuit of the less loaded bucket rod, so the speed of the bucket rod is faster than that of the boom, which makes joint operation difficult. When the bucket rod and bucket are operated at the same time, the speed of the bucket rod is much faster than that of the bucket because the bucket rod is operated by two pumps in a combined flow and the bucket is operated by a single pump, which makes the combined operation difficult. The function of the bucket rod throttle valve is to open the bucket rod throttle valve and limit the pressure oil flow to the bucket rod-high-speed control valve during the combined operation, which limits the speed of the bucket rod, improves the combined operation performance and the working principle of the bucket rod throttle valve.
(1) When operating the bucket rod alone, the walking shuttle valve does not flow out the pilot pressure oil, and the bucket rod throttle valve does not work. The pressure oil from the rear main pump flows through P and all the ports flow to the bucket rod-high-speed control valve.
(2) When both the bucket rod and the boom or the bucket rod and the bucket are operated at the same time, the pilot pressure oil from the travel shuttle valve pushes the sliding valve of the bucket rod throttle valve to the right. Therefore, the pressure oil flowing from the main and rear pump to the bucket rod-high-speed control valve is throttled, and the speed of the bucket rod is controlled, which improves the joint operation performance.
Retaining valve for small loose arm
(1) Function: To prevent the boom from sliding naturally when it is in the lifting position.
(2) The boom retaining valve consists of safety filling valve, pilot missile spring, pilot spool, lift spring and slide valve as shown in Figure 2-18.
(3) Working principle.
(1) When the boom is lifted, the pressure oil from the main operating valve flows to V port, overcomes the force of lifting spring 4, pushes the sliding valve 5 upwards and flows to the lower chamber of the boom cylinder through C and port, and the boom starts to lift.
(2) When the boom is in the lifting position and the lever returns to its center position, the sliding valve 5 moves downward by lifting the spring 4 and closes the oil circuit in the lower chamber of the boom cylinder. At the same time, the pressure oil in the lower chamber of the boom cylinder enters the inner chamber B of the sliding valve 5 through the orifice a on the sliding valve 5 and is closed by the pilot valve spool 3. As a result, the booster kidney remains in the lifting position to prevent the boom from sliding down.
(3) When the boom is lowered, the pilot pressure oil from the PPC valve pushes the pilot spool 3 to the left so that the pressure oil in the B chamber of the spool 5 is drained back to the tank through the channel opened by the pilot spool 3.
The pressure oil in the lower chamber of the boom cylinder enters the B chamber through the orifice a on the spool valve 5. The pressure oil drops through the orifice a. When the pressure in the B chamber drops below the pressure in the V port, the spool valve 5 opens and the pressure oil from the lower chamber of the slave arm cylinder flows through the Cv port to the V port and then into the main operating valve. When abnormal pressure occurs in the lower chamber circuit of boom cylinder, the safety filling valve opens to protect it.
