|
Posted by Paul on July 19, 2008, 2:42 pm
wrote:
>
>
> >I understand that some building jurisdictions require that pressure
> > relief valves be installed on tankless water heaters, but other
> > jurisdictions do not require this. The manual for my Weil-McLain
> > boiler does not call for one. I can understand a pressure relief valve
> > on a vessel such as a boiler, but why put a pressure relief valve on
> > the cold water pipe going to a tankless heater? A tankless heater is
> > just a coiled pipe with fins. What could possibly raise the pressure
> > to the point that the pipe explodes?
>
> =A0 =A0Expansion. The scenario that gives birth to pressure relief you
> describe, is an isolated volume of fluid at a nominal temperature
> with no means of expansion relief (100% fluid w/no air chamber)
> =A0then raising the temperature of the fluid (which increases the
> volume) without increasing the physical space this fluid
> occupies. Something's gonna give.
>
> -zero
Yes, something will give when the pressure eventually exceeds the
strength of the materials. However, in this system, the burner heats
the boiler water and the hot boiler water heats the tankless heater
which is simply the portion of the cold/hot water piping system that
is coiled inside the boiler. The coil is always under elevated
pressure from the heated water. Since the boiler has a pressure relief
valve, that should limit the temperature of the water in the boiler
and therefore limit the temperature and the pressure of the water in
the tankless coil. The small volume of the coil can stand a lot more
pressure than the large volume of the boiler, so how can the pressure
in the coil get high enough to rupture the coil?
I suspect that tankless heater pressure relief valves are meant for
systems where the heating is done by heating elements rather than by
hot boiler water.
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap