This fits your .

1/2", Lead Free, Water Service Vacuum Relief Valve, Allows Air To Enter A Closed System To Automatically Relieve Vacuum Conditions Which Could Siphon The Water From The System and Burn Out A Water Heater Or Collapse A Tank, CSA, ANSI and Massachusetts State Code Listings.

Vacuum Release Vlv 1/2 - B071XNGPXB