Hydraulic bending press

Claim 1

A hydraulic press for bending plates and the like, comprising, in combination, an upper and a lower apron, one of said aprons being designed selectively to rise and to fall by the action of a single-acting hydraulic pressing cylinder, return movement of said one apron being effected by the apron''s own gravity, a plurality of plunger pumps driven in different shifted phases alternatively by respective swash discs, a first hydraulic cylinder of the first one of said plunger pumps connected with a first fluid path to said pressing cylinder for actuating said one apron through a check valve while one end of a second fluid path, from a second hydraulic cylinder of the second one of said plunger pumps is connected with said first fluid path to said pressing cylinder, for actuating said one apron through a lowerpressure check valve so as to permit hydraulic fluid to flow from said first cylinder, the other end of said second fluid path being connected with a drain circuit through a higher-pressure check valve, the working characteristics of said one apron being changed over so that, in the casE of said one apron being loaded lightly such as for approaching one of upper and lower molds, said one apron works with a lower pressure and a higher supply rate, whereas in the case of said one apron starting the press work, the fluid supply from said second cylinder is discharged without noteworthy resistance, and only the fluid supply from said first cylinder is introduced into said pressing cylinder so that said one apron works with a high pressure and a lower supply rate.