Low-overload piston type high-low pressure actuating device

The invention belongs to the field of actuation launching, and particularly relates to a low-overload piston type high-low pressure actuation device. A section of variable-section pull rod is additionally arranged on the inner side of the piston on the basis of a traditional bomb pushing piston, one end of the pull rod is fixed to the piston through threads, and the other end of the pull rod is inserted into a throwing bomb. The outer circular surface of the piston is provided with two equal-depth grooves so that the O-shaped sealing ring can be conveniently installed, and the piston is provided with a corresponding fixing pin hole so that a fixing pin can be conveniently inserted into the fixing pin hole. Internal and external threads are machined on the pressure limiting diaphragm and connected with the variable cross-section pull rod and the throwing bomb respectively, and the diaphragm is provided with a prefabricated weak ring convenient to shear. According to the device, the fixed size of a fuel gas noz