Outlet and Relief valve

Outlet noun - A place or means of going out.

Relief valve and outlet are semantically related In some cases you can use "Relief valve" instead a noun "Outlet".

Relief valve noun - A valve in a container in which pressure can build up (as a steam boiler); it opens automatically when the pressure reaches a dangerous level.

Outlet and relief valve are semantically related in release for something at dangerous level topic. You can use "Outlet" instead a noun phrase "Relief valve".