1.Pilot control handle spool stuck
The reason for unilateral non-rotation is that the valve core in the pilot control handle is stuck. At this time, we can use the pilot oil of other actions (such as bucket rod) to test or judge by measuring the secondary pilot pressure. This situation is relatively simple to judge.
2.Problem with shuttle valve
The release brake requires pressure oil at the SH port, and the source of the SH is generally rotary pilot oil obtained through the shuttle valve. In addition, some models will use shuttle valve to limit some actions, such as rotary limit bucket rod recovery. In two cases like this, if the shuttle valve problems, there will be unilateral can not turn.