1) The working pressure of the gasoline pump of the four-column hydraulic machine is low. When the roller is running downward, the bottom end of the downward movement has been opened. Coupled with the weight of the roller itself, the roller slides downward. However, when it returns, due to the low pressure of the fuel pump, the roller can gradually rise.
2) There is a problem with the four-column hydraulic machine relay. When the valve assembly (relay, software) is quickly removed, the key is that the roller cannot return.
3) When there is any problem with other relays or components connected to the system, the roller cannot return because it cannot form an efficient return pressure.
4) When the filling valve cannot be opened, the four-column hydraulic roller cannot return, but the system will have very good pressure at this time, which is very easy to judge.
