water pressure regulator question

[neporcupine]

I am installing a water pressure regulator right after main inside main water shutoff. I am not required by code to have a check valve, so I am not doing this. I understand it is standard to put an expansion tank on the water heater as well, so I will also likely do this. However, I was reading the instructions on my watts pressure reducing fitting model “LFN45BUM1”. See the photo under “bypass feature”. They seem to be claiming that their fitting is able to accommodate any thermal expansion. Am I right in my interpretation of their package insert? If so, is it that it has been found to be inadequate, so plumbers install an expansion tank anyways? Thanks!

 

[Rossando]

If you add a PRV valve you must install expansion tank to the cold side and strap it up so it's not just supported by the pipes. Or unless your local code states otherwise. Once you close off the system with a PRV you need a way to allow thermal expansion...

 

[neporcupine]

If you add a PRV valve you must install expansion tank to the cold side and strap it up so it's not just supported by the pipes. Or unless your local code states otherwise. Once you close off the system with a PRV you need a way to allow thermal expansion...

I appreciate the response, but I know all that. My question is whether this PRV in its own literature is claiming to obviate the need for the expansion tank. Again, I’m skeptical and will put in an expansion tank anyways, but just curious what they are claiming here.

 

[Twowaxhack]

If your starting pressure upstream(from the meter)of the pressure reducing valve is over 80 psi for a potable water inside the homes foundation footprint then you need a way to control thermal expansion.

Even though the PRV may have a bypass, the valve can’t bypass and keep the pressure below the max 80psi allowable pressure inside the homes footprint.

For example. If your starting pressure was 65psi and you wanted to add a PRV to reduce that pressure to 50psi but you don’t mind if the pressure temporarily exceeds your set point during thermal expansion then you wouldn’t need thermal exp. Control. The bypass of the PRV if equipped would allowed this expansion to be relieved back into the water supply and still be within the 80psi max.

This is true if there are no other check valves and the system is open.

 

[neporcupine]

If your starting pressure upstream(from the meter)of the pressure reducing valve is over 80 psi for a potable water inside the homes foundation footprint then you need a way to control thermal expansion.

Even though the PRV may have a bypass, the valve can’t bypass and keep the pressure below the max 80psi allowable pressure inside the homes footprint.

For example. If your starting pressure was 65psi and you wanted to add a PRV to reduce that pressure to 50psi but you don’t mind if the pressure temporarily exceeds your set point during thermal expansion then you wouldn’t need thermal exp. Control. The bypass of the PRV if equipped would allowed this expansion to be relieved back into the water supply and still be within the 80psi max.

This is true if there are no other check valves and the system is open.

I see, well explained, thanks!