Stick throttle
In the four-way directional valve, the bucket controls the spool. When manipulating the boom and the stick at the same time, most of the pressure oil flows to the stick oil path with a smaller load, so the speed of the stick is faster than the speed of the boom, making joint work difficult. When operating the stick and the bucket at the same time, since the stick is a dual-pump combined oil supply operation, and the bucket is a single pump oil supply operation, the speed of the stick is much faster than the speed of the bucket, which makes the joint operation difficult . The function of the stick throttle valve is to open the stick throttle valve to limit the pressure oil flow to the stick-high-speed control valve during joint operation, which limits the speed of the stick and improves the joint operation performance. Working principle of rod throttle valve.
(1) When the stick is operated alone, there is no pilot pressure oil flowing out of the walking shuttle valve, the stick throttle valve does not work, and the pressure oil from the rear main pump flows to the stick-high-speed control valve through P and the port.
(2) When the stick and boom or stick and bucket are operated simultaneously, the pilot pressure oil from the travel shuttle valve pushes the spool of the stick throttle valve to the right. Therefore, the pressure oil flowing from the main rear pump to the stick-high-speed control valve is throttled, the stick speed is controlled, and the joint operation performance is improved.
Small loose arm holding valve
(1) Function: When the boom is in the lifted position, prevent the boom from sliding down naturally.
(2) The boom holding valve is composed of a safety charge valve, a pilot spring, a pilot spool, a pop spring, and a spool valve, as shown in Figure 2-18.
(3) Working principle.
①When the boom is raised, the pressure oil from the main operation valve flows to the V port, overcomes the force of the lift spring 4, pushes the spool valve 5 upward, and flows to the lower chamber of the boom cylinder through port C, The arm begins to lift.
②When the boom is in the lifted position and the joystick returns to the neutral position, the spool valve 5 is moved downward by the force of the lift spring 4, and the oil path of the lower chamber of the boom cylinder is closed. After the pressure oil enters the cavity b of the spool valve 5 through the orifice a on the spool valve 5, it is closed by the pilot spool 3. As a result, the kidney is kept in the raised position to prevent the boom from sliding down.
③When 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 cavity b of the spool valve 5 is discharged 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 chamber b through the orifice a on the slide valve 5. The pressure oil generates a pressure drop when passing through the orifice a. When the pressure in the chamber b drops below the pressure of the V port, the oil The valve 5 opens, and the pressure oil from the lower chamber of the boom cylinder flows to the V port through the Cv port, and then flows into the main operation valve. When abnormal pressure appears in the lower cavity circuit of the boom cylinder, the safety charge valve opens to protect it.
