The small hydraulic control valve and safety valve may leak.
If your press brake has been used for several years, the sealing ring in the oil cylinder is aging, resulting in internal leakage.
Another point is whether someone has moved the overflow valve of the machine. If it is loosened to the end, it will automatically slide down.
Another question is whether the three-position four-way directional valve is adjustable. If it is adjustable, we have to check whether there is a problem with the return trip.
Machines with a long time are mostly internal leakage.