When the press works under the nominal pressure, the oil pressure in the hydraulic pad is less than the back pressure of the unloading valve (or balance valve), and the press works normally.
When the press is overloaded, the oil pressure in the hydraulic pad increases, and the pressure is greater than the back pressure of the unloading valve (or balance valve), forcing the spool of the unloading valve (or balance valve) to move, the hydraulic oil in the hydraulic pad is discharged back to the oil tank, the press is unloaded rapidly, and the connecting rod seat moves a certain distance relative to the sliding block. This not only protects the press, but also avoids damage to parts due to overload.
