pressure relief valve 123 is likewise connected to the hydraulic circuit and is set to open if an excessive pressure is produced by the booster 62 such an overpressure condition might occur if the booster were actuated to pump an additional quantity of hydraulic fluid to the hydraulic cylinder 22 of the rotary actuator 19 after the piston 23 of the pneumatic cylinder 21 had been moved to the left into contact with the stop 28 still referring to fig5 the counter circuit 93 includes three counters 127 129 which may be set by means of thumbwheel switches 131 133 to any desired count number the first counter 127 receives impulses indicative of the operation of the sealant pump from the pressure actuated switch 99 via the signal line 134 this counter 127 also includes two normally open switches 136 137 these switches close when the counter 127 has received the pre selected number of pulses from the pneumatic switch 99 the first of these switches 136 is connected to the signal line 134 and thereafter transmits the signals from the pneumatic switch 99 to the input of the second counter 128 via the signal line 138 the second switch 137 is connected to a source of power and upon closing connects the normally closed switch 139 of the.