The Fisher 289H-42 Pressure Relief Valve is a protective valve designed to help regulate and safely release excess pressure in compatible gas and HVAC system applications. It operates by opening when system pressure reaches a predetermined level, allowing excess pressure to escape and helping protect connected equipment. Commonly used in gas pressure regulation systems serving furnace... https://www.partshnc.com/fisher-289h-42-1-npt-regulator-4-15-psi