The hydraulic system principle of the 200t hydraulic press, as shown in the figure, operates as follows: with the manual directional valve 5 handle in the middle position, hydraulic oil flows back to the tank from the pump output, keeping the system unloaded. During this time, the hydraulic check valve maintains pressure in the plunger cylinder. When the directional valve 5 handle is in the right position, the pump supplies hydraulic oil to the plunger cylinder 3 through the hydraulic check valve, causing the table to rise. The pilot-type unloading relief valve 2 adjusts to control the system pressure to 2MPa. The gear pump 1 unloads, and the manual piston pump 8 supplies oil to pressurize the plunger cylinder 3 with a small flow, adjusting the pressurization pressure through the pilot unloading relief valve 2.
When the handle of directional valve 5 is in the left position, oil flow enters the control circuit of the hydraulic check valve. The direct-acting relief valve 7 adjusts to open the superimposed hydraulic check valve 6, allowing the plunger cylinder 3 to return under its own weight. And because of the superposition-type pilot-controlled check valve 6 for the pilot-type valve, in the main spool before opening, the first to open the pilot spool area is small, so the plunger can be unloaded first when the plunger cylinder pressure to prevent the pressure shock.
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