There is absolutely no pressure. The internal control control oil pressure is zero, because the M-type directly returns to the oil tank. In order to solve this problem, it is necessary to install a check valve in the oil return pipeline. The required opening pressure is greater than the opening pressure of the pilot valve of the electro-hydraulic reversing valve, which is generally very small, so I can't remember it clearly. It seems to be 0.4bar, not absolute.