Back to Type "A" and "B" Gates   "A" Gate Sequence of Operation When the actuating means (palm buttons or foot switch) is operated, air pressure is released from the bottom of the gate operating cylinder. This allows the gate to descend by gravity. Once the gate is fully down, a "gate-down" proximity switch senses this and the machine is allowed to make a stroke. If the gate cannot complete its downward travel, this "gate-down" proximity switch will not sense the gate and will prevent a machine cycle. If the actuating means is released before the machine starts its cycle, the gate returns to the full open position. When the machine is actually making a stroke, air pressure is applied to the top of the gate-operating cylinder which in turn holds the gate down and prevents it from being raised until the machine has completed its cycle. If the machine malfunctions and does not stop at top dead center, the gate remains in the closed position. According to ANSI, the gate must open after every cycle in order to reset the antirepeat system. If this does not happen, the machine will not make another stroke. To accomplish this, the gate control requires a signal from the machine at top dead center. This signal is normally obtained from a photo-sensor or limit switch operated by a cam located at top dead center in the machine cycle. Actuation of the limit switch is accomplished by the rotation of the crankshaft or any other member of the machine which makes one revolution or oscillates one direction per stroke.     "B" Gate Sequence of Operation The Type "B" Gate operates in a similar manner as the Type "A' Gate. When the actuating means (palm buttons or foot switch) is operated, air pressure is released from the bottom of the gate-operating cylinder. This allows the gate to descend by gravity. Once the gate is fully down, a "gate-down" proximity switch senses this and the machine is allowed to begin the stroke. If the gate cannot complete its downward travel, this "gate-down" proximity switch will not sense the gate and will prevent a machine cycle. If the actuating means is released before the machine starts its cycle, the gate returns to the full open position. When the machine is actually making a stroke, air pressure is applied to the top of the gate-operating cylinder which in turn holds the gate down and prevents it from being raised until the machine has reached bottom dead center. The gate must open every cycle in order to reset the antirepeat system. The sequence for this is the same as the "A" Gate.