On Mar 29, 3:11 pm, "Toller" wrote:
"BobK207" wrote in message

oups.com...



Adding a back flow preventer or a check valve to a domestic water
supply will create a closed system.

Usually the issue of thermal expansion in a close system is handled by
installing an expansion tank on the cold water side of the water
heater.

Could the thermal expansion in the system be handled by installing a
pressure relief valve; with a relief pressure lower than the relief
pressure of the T/PO valve of the water heater?

Of course this relief valve would dump a small amount of water every
day...... approx the amount of expansion of the cold water heated to
water heater temp.

Is the expansion tank solution "better" than the relief valve
solution? or is a relief valve a better solution?

I'm just curious........... since I can see if the relief valve is
working but the behavior of the expansion tank is internal & thus
hidden.....so I have to go on faith as to whether the expansion tank
is doing it's job.

There was one on the market that dumped excess water/pressure into the
toilet. I don't know if it is still available.
My pressure reduction valve has a backflow valve on it, so if the pressure
downstream exceeds the pressure upstream you get water flowing backwards to
relieve the pressure. Of course, if you have a backflow prevention valve
that won't help you any.
My supply is 90psi and I have the valve set to 55psi. When I let the hw
tank cool off and then turn it up higher than normal, the pressure in my
house never exceeds 85psi. I figure that is the worst case senerio, so I
don't see I will ever need the back flow valve and certainly not an expansion
tank.
You might want to try testing it before doing anything drastic.

I just re-did my domestic water service entrance and all the interior
fresh water plumbing.

I installed a pressure reducing valve (that has back flow bypass
capability) but I installed a check valve upstream of it to protect
the municipal supply from any back flow.

The city supply is about 75 psi but I've seen it as high as 90 so I
have my PRV set to 60.

With the closed system I needed some way to handle the expansion
pressure......I opted for the relief valve because I didn't like the
rubber bladder idea (why I don't know)

The plumber working on this with me was ok with the relief valve
instead of the expansion tank.


I guess we'll see how this all works out.


cheers
Bob