the h bar will engage and close microswitch 81 microswitch 81 is interposed in line e2 as shown in fig8 so that closure of switch 81 is required in order to continue any further operating sequence of the machine as shown microswitch 81 is connected in series with a second foot treadle switch sw3 upon closure of the treadle switch sw3 the circuit will be closed thereby enabling solenoid valves sv2 and sv3 to be operated and in turn control operation of the clamp cylinders 26 and driver cylinders as will be described below when the operator is satisfied that the boot and heel are properly positioned on the jack he then actuates treadle switch sw3 to simultaneously energize clamp solenoid valve sv2 and vent solenoid valve sv3 as described above it is a desired feature of operation of the machine to sequence operation of the clamp cylinder 26 and drive cylinder so that the clamp cylinder first moves downwardly into engagement with the heel to hold the heel under a relatively light pressure i e 125 p s i oil pressure after the operator is satisifed that the parts of the shoe are in a properly oriented clamped configuration the operation of the system calls for the exhaust end of clamp cylinder 26 to be blocked off by a power check valve pcv with power check valve shifted to obstruct flow from the head end of the clamp cylinder 26 the nail drive cylinder is actuated to drive the nails upwardly into the heel but only under just that amount of force necessary to that end the control circuitry includes a high pressure relief valve v1 which is connected across the hydraulic line h1 and hydraulic return h2 the pressure control.