Hydraulic control appliance for hydraulic shovels etc. has arrangement to prevent load from falling without connected overload relief valve

摘要

The appliance has a branch passage (18) to connect the pressure chamber (3a) of the cylinder unit (3) to a load holder (5) between control valve (2) and pilot return valve (7). First reversing elements block the branch during normal operation, and connect the pressure chamber of the pilot valve to the load holder via a throttle (20). Second reversing elements maintain the pressure in the counter pressure chamber of the valve to the level of the load pressure in the cylinder unit pressure chamber, and to drain the hydraulic oil from the counter pressure chamber. Both reversing elements are formed so that the control valve is switched by the pilot pressure.