Analysis on the selection of the middle position function of the hydraulic reversing valve
The neutral function of the reversing valve not only affects the working state of the hydraulic system when the spool is in the neutral position, but also affects the working performance of the hydraulic system when the reversing valve is switched from one working position to another. In other words, choosing valves with different median functions will congenitally have some irresistible failures. On the contrary, if the selection is good, certain failures can be eliminated and prevented.
①The problem that the system can maintain pressure and cannot maintain pressure (system interference problem). When the interface P connected to the hydraulic pump can be disconnected by the neutral function, the system can maintain pressure, and the hydraulic pump can use the multi-hydraulic cylinder hydraulic system without interference; when the port P and the port O of the oil tank Or when T is connected but not unblocked, the system can maintain a certain lower pressure for the use of control oil; when P and O are unblocked, the system cannot maintain pressure, and valves with these intermediate functions will not be able to Anti-tamper circuit for multi-cylinder systems.
②System unloading problem. When the reversing valve selects a valve whose neutral function is that port P and port O (or T) are unblocked, the hydraulic pump system can be unloaded to prevent the oil from heating. But at this time, it cannot be used in a multi-hydraulic cylinder system, otherwise other hydraulic cylinders will fail to move or change direction.
③Commutation stability and commutation accuracy problems. When a valve with a neutral function that can close ports A and B is selected, hydraulic shock is likely to occur when the hydraulic cylinder changes direction, and the stability of the changeover is poor, but the changeover accuracy is high; on the contrary, when both A and B are connected to 0 , During the reversing process of the hydraulic cylinder, it is not easy to brake quickly, and the reversing accuracy is low, but the reversing stability is good, and the hydraulic shock is also small.
In addition, in the reversing circuit using the electromagnetic reversing valve, the suction force of the electromagnet is used to push the valve core to make relative movement in the valve body to change the working position of the valve to realize the reversing of the actuator. It switches quickly and the reversing time is short, so when the reversing is switched, hydraulic shock and reversing shock will inevitably occur. At this time, it can be improved by using a manual reversing valve or an electro-hydraulic reversing valve with damping: the former can gradually open or close the valve port because it can push the valve core to move faster than the valve body with the hand-operated lever. , has throttling, damping, and buffering functions, which have been verified on multi-way valves commonly used in construction machinery; the latter electro-hydraulic valve not only retains some advantages of solenoid valves, but also slows down the main switching speed by adjusting the damping. The switching speed of the directional valve (hydraulic valve). Both can reduce the magnitude of the shock.
④Starting stability problem. When the reversing valve is in the neutral position, if a certain cavity (or A or B cavity) of the hydraulic cylinder is connected to the oil tank and the shutdown time is long, the oil in this cavity will flow back to the oil tank and a cavity will appear. The buffering effect cannot guarantee a smooth start, and the opposite situation is easy to ensure a smooth start.
⑤The hydraulic cylinder stops at any position (it can be stopped accurately) and the problem of "floating". Many hydraulic machines, such as pumping machines, sometimes encounter emergency situations and require hydraulic cylinders to stop, and stop accurately, and stop at any position. When the central function (O type) with ports A, B, P and port O closed, it can stop at any position. And like A, B, P and O are connected or semi-connected (such as H, X type) can not, at least can only maintain a floating state.
