Pressure relief valve and pressure vessel

[Jimbob1235]

Hi, I was just wondering if anyone on here has an answer to a question for me. Why is a pressure relief valve on an unvented electric hot water tank located on the cold water intake rather then the hot water out let? And also does anyone have any ideas why some unvented hot water tanks comes with no pressure vessel for when the water exspands under high temps. Thanks.

 

[SJB060685]

The PRV and vessel are connected in after the pressure reducing valve and double check valve. They could be connected further downstream but installed there so they’re not exposed to higher temperatures.
Some tanks have an inbuilt air gap at the top of the cylinder rather than an external vessel. In this particular design if the air gap was lost and unable to be recharged then an external vessel would be installed, or replace the whole cylinder.