This invention relates to a flapper check valve having a valve housing which has at least one outlet opening. A valve backer plate having a plurality of arcuate backer through holes is positioned generally parallel to a valve port plate having a plurality of arcuate port through holes. The valve port plate and valve backer plate are sealably secured with respect to the valve housing. In an open position of the flapper check valve, the backer through holes are in communication with the port through holes. At least one peripheral spacer/hermetic seal is positioned at a generally peripheral location relative to the valve port plate. Upon combustion within the combustion chamber, the flapper check valve prevents fluid/gas backflow in a direction from the valve backer plate to the valve port plate. At least one flat central spacer is positioned at a generally central location relative to the valve port plate and the valve backer plate. A plurality of inner spacer/guide pins are positioned on an interior surface of the valve port plate. The inner spacer/guide pins provide sufficient support to the valve backer plate whereby the valve backer plate can have a reduced thickness and still resist deflection when the valve backer plate is subjected to relatively high pressures from within the valve housing during a combustion cycle within the combustion chamber.