Hydraulic drive

A hydraulic drive for a tool, the hydraulic drive comprising:

• a pump;
• a valve arrangement including a pressure limiting seat valve and a switching seat valve;
• a working chamber;
• a piston in the working chamber, the piston being adapted to be acted upon on one side thereof against a permanent load by the pump, which is operable in a switch-off mode, via the valve arrangement;
• a pressure line from the pump to the working chamber;
• a restriction provided in the pressure line, wherein the pressure limiting seat valve is configured to respond exclusively to pressure originating from a volume flow in the pressure line upstream of the restriction;
• a tank connected to the pressure limiting seat valve on a flow-off side;
• a drain line connected to the pressure line downstream of the restriction, the drain line leading from the working chamber via the switching seat valve to the tank;
• wherein a closing side of the switching seat valve is adapted to have applied thereto pressure from the pressure line upstream of the restriction, an opening side of the switching seat valve is adapted to have applied thereto a force generated when the pressure limiting seat valve responds, the pressure limiting seat valve has on a spring-loaded valve piston a first pressure application surface, which is adapted to be acted upon by pressure from the pressure line and usable for limiting a maximum operating pressure in the working chamber, and a second larger pressure application surface for keeping the pressure limiting seat valve open, after the pressure limiting seat valve has responded, at least until the pump is switched off, and the pump is adapted to be switched off when a maximum operating pressure has been reached;
• and
• a restriction means provided on the flow-off side of the pressure limiting seat valve to the tank for increasing pressure from the pressure line acting on the second pressure application surface of the pressure limiting seat valve, wherein the force on the opening side of the switching seat valve can be generated either mechanically or hydraulically by the pressure limiting seat valve from a raised pressure, when the pressure limiting seat valve responds and when it is kept open.