Universal 403 series anti-siphon valve NPT(F) ports cast iron - all sizesUniversal 403 series anti siphon valve NPT(F) ports cast iron all sizes PR (pressure relief models) opens at 15 to 35 psi Reducing fire hazards and preventing fuel spillage should a line rupture The flow would automatically stop the syphon effect No need to specify head settings Everything is included to cover an operating range of 0 to 20 Automatic shut off syphon effect Precision machined valve seats Prevents fuel spillage No need to specify head