Relief Valves Click on desired biogas equipment to view features, specs, options and download documents. 8800 Pressure-Vacuum Valve & Flame Arrester 8820A Pressure – Vacuum Valve & Flame Arrester (pipe-away) 1200A Biogas Pressure – Vacuum Relief Valve 1220A Biogas Pressure – Vacuum Relief Valve with Pipe-Away 2300A Biogas Pressure Relief Valve – Weight Loaded 12E-TWW-0 Biogas Pressure – Vacuum Relief Valve Vent to Atmosphere 12F-TWW-0 Biogas Pressure – Vacuum Relief Valve with Pipe-Away