These nitrous PCE check valve spacers serve two distinct functions. These spacers provide the benefits of an open carburetor spacer, but also incorporate a check valve that will vent pressure between 75-90 psi for backfire protection with direct port and plate-type nitrous systems. Our check valves eliminate the need to replace the burst panels if you should have a backfire. Never replace burst panels again. Use of these spacers is the only way to meet the requirement by the IHRA and other sanctioning bodies for burst panel protection when using a direct port type nitrous system on a cast intake manifold. These lightweight spacers are precision-machined from billet aluminum with a military spec hard coat for durability and corrosion resistance.