Bell & Gossett 113021 87 Automatic Air Vent 1/2" FPT or 3/4" MPT NPT 150 PSI Max MAXIMUM WORKING PRESSURE 150 PSIG MAXIMUM OPERATING TEMPERATURE 240°F MEASURES 4-3/4" X 2-1/4" The #87 vent is designed to vent the accumulation of troublesome air wherever it can be trapped.