The ignitor in a dryer prevents the secondary coil from opening. When the radiant sensor shuts off the ignitor, the current flows thru all 3 valve coils to open the gas valve. The dryer valve uses 120 volts.
The oven uses the ignitor in series with the gas valve, as only 3.3 volts are needed to open this valve. The ignitor must stay energized to keep the valve open.