1.At present, the injection chamber of the single hydraulic prop is the inner cavity of the living column, and the prop need to inject a large amount of working liquid to raise the living column. When it falls, it need to drain a large amount of working liquid to fall. The structure is complicated and the column speed is slow.
2. The return spring in the prop is in contact with liquid for a long time during use, it's easy to rust. Thereby shortening the service life of the single hydraulic prop. The damage inside the living column is difficult to observe and repair.
