Application and classification The development of the steering system of the loader is mainly to assist the steering system, load sensing hydraulic steering and priority valve steering system, flow amplification steering system 3 types, the following load sensing hydraulic steering and priority valve steering system Priority valve and its development - priority unloading valve and the level of unloading priority valve for description and analysis. Priority valve priority valve structure shown in Figure 1a mainly by the steering safety valve, spring, valve and valve body. Its working principle shown in Figure 1b, in which P port for the steering pump inlet, CF port and steering gear into the oil port, EF port and working system multi-way valve into the port connection, LS port and steering control port connection T port for the safety valve back to the mouth. When P port into the oil, hydraulic oil preferentially supplied to the CF port by the spool 3. When the steering gear does not work, CF port is closed, then LS port pressure is zero, the right end of the spool into the oil, the hydraulic force acting on the right side of the spool to overcome the preload of the spring 2, the valve spool to the left, At this point P port and EF port connectivity, steering pump oil confluence to work in the system to achieve dual-pump confluence. When the steering gear work, CF port steering gear connected to the steering cylinder, steering pump oil into the steering cylinder, the loader steering; LS port pressure signal through the throttles hole in the left end of the spool, then the spool The pressure at the right end is lower than the pressure at the outlet of the steering gear. Due to the pressure difference between the left and right ends of the valve spool and the action of the spring, when the speed of the steering gear is very high, the valve spool is moved to the right to close and the hydraulic oil is preferentially supplied to the steering. When the steering load exceeds the rated value, the pressure of LS port of the oil to the steering safety valve 1 open, LS port pressure relief valve spool to the left, the steering pump to join the oil flow system. When the work system is not working, the multi-way valve in the neutral position unloading. However, the load-sensing hydraulic steering and priority valve steering system in the work of the system under high pressure and low flow conditions, the confluence of the oil to the work of the system to go redundant, at this time the steering system to withstand the same work system high pressure. To this end on the basis of the priority valve, an increase of high-pressure unloading part, it has become a priority unloading valve. Preferential unloading valve priority unloading valve structure shown in Figure 2a, the main increase in the unloading safety valve, one-way valve spring, unloading unloading valve, unloading valve, unloading valve spring and other components. Its working principle shown in Figure 2b, when the working system is in high pressure state, EF port is also in a high pressure state, the high pressure oil opens the unloading relief valve unloading equivalent valve 3 and unloading relief valve 1 contact; when the pressure exceeds the unloading safety valve Set the pressure, unloading safety valve open, the oil return brough the oil b to the left unloading spool 4 to overcome the unloading valve spring 5 spring force to unload the valve to the right, high pressure oil port EF directly through the T port discharge Load tank. In this way, the problem that the high pressure of the priority valve can not be unloaded is solved, the working condition requirement of high pressure and small flow is realized, and the energy is saved. However, it should be noted that when the system is not in operation, that is, when the loader is in high-speed shipping condition, the steering pump oil is still unloaded by the multi-way valve, and this condition often occurs when the loader is working. Low pressure unloading structure based on high pressure unloading. Low and high pressure unloading priority valve in the AA position in Figure 2a added a low pressure unloading components, as shown in Figure 3. When the EF port is under low pressure (usually below 2MPa), the system is not working. The pressure oil in the port EF passes through the left Ø4 hole, passes through the valve hole to the oil passage b, and pushes the unloading spool directly back to the tank. When the pressure of the EF port exceeds 2MPa, the system is in the working state. The pressure oil is pushed through the Ø4 hole on the right side to move the valve core to the left against the spring resistance, so that the hole on the left side Ø4 is closed and the oil flow in the b channel is not flowing, Spool in the left position, EF port does not unload, the pressure oil flow to the working system. More Keywords Search: Valve