The Electro-hydraulic Directional Valve of the surface grinder is composed of the solenoid slide valve of the pilot valve and the hydraulic slide valve of the main valve. This system controls the oil circuit by reversing the pilot valve of the surface grinder. The oil flow direction of the control oil circuit does not change, the directional valve is always kept at the original end, the direction of the main oil circuit does not change, and the worktable can always move forward. Once the control oil circuit switches the direction, the main valve spool will move to another operation direction according to the preset speed. If the direction of the main oil circuit changes, the worktable will reverse movement, avoiding the reverse 'dead point'.

In this way, the kinetic energy of the large inertia worktable can be converted into heat energy and consumed through the saving effect. The size of the control oil port of the main valve of the electro-hydraulic reversing valve is adjustable, that is, the reversing time △ t can be extended. It can effectively reduce the commutation impact, so this commutation method is dominant for a long time. However, the commutation parameters can only be set in advance and can not be changed according to the change of working conditions, which is impossible to complete the ideal commutation for the system whose working conditions change at any time.

The surface grinder adopts the hydraulic transmission reversing system of electro-hydraulic proportional valve. The purpose of reducing the speed by automatically reducing the flow and achieving smooth and impact free commutation at the end is completed. An intelligent control commutation system can also complete the ideal commutation when the working condition is changed. This hydraulic transmission reversing system completes excellent intelligent control of the output displacement or speed, which makes the reversing process controllable, so it has a very wide application scale.