What is this?

On water heater. Is this a anti siphon or vacuum break? If yes is it common to see them leak? I see so many different styles it seems and they always are leaking like this one.






corrosion is due to absence of a required dielectric nipple out of tank
cprv not to be used in lieu of tprv
was the required tprv side mount installed?
if no tprv is present the owner has a serious life safety a property loss explosion potential that requires immediate repair! they should be notified of the hazard

galvanic corrosion is due to absence of a proper nipple and separation protection between dissimilar metallic tank, fittings and piping materials

hopefully the calibrated pressure relief valve is not attempting to replace a temperature & pressure relief valve (tprv)

if this is the case a life safety and property loss condition probably exists and the owner should make immediate necessary retrofit replacement with a proper nipple and tprv if the tank fitting hasn’t been overly compromised by the corrosion that would then require water heater replacement, imo

It’s an old adjustable safety pop off valve.
I haven’t seen one in years.
It really should be replaced.

cool thanks i will look that up