In the middle, all oil ports are open, and the system has no oil pressure. Functional features: 1. The oil inlet P and the oil return port T are all connected with the working oil Inlet A and B, making the working machine form A floating state and can move under the action of external force, can be used for mechanism with handle. 2. Hydraulic pump can be unloaded. 3. Impact from stop to start. Because when the working mechanism stops, the oil in the oil return chamber has flowed back to the oil tank, and no oil plays a buffering role. When braking, the oil ports communicate with each other, so the braking is more stable than O-type. 4. For single-rod double-acting Oil cylinder, because the effective action area on both sides of the piston varies, the sliding valve with this function cannot completely ensure that the piston is in a stop state.