Home → Tank Trailer Products → Vents → Master Blaster 407 → Swivel Nut → 4" Assembly → Pressure Relief Valve - 4" Master Blaster - Stainless Steel - Female NPS Swivel Nut - 25PSI MAWP/30 PSI Set Pressure/4HG - Includes 1/4" FNPT Gauge Port & 3/4" FNPT Ball Valve Connection - Rain Cover Installed - Pressure & Vacuum