On 1/8/2010 9:09 AM, Jim Healy wrote:
A little off the point of contaminated potable water, but hopefully of
interest. We run with our house water pump turned off all the time, every
time. It's part of our pre-departure checklist. The reason is that the hot
water tank, an Atwood, has a safety pressure relief (pop-off) valve on it that
is pre-set at 185 degrees. When the engine is running, the engine coolant is
in that temp range. Several years ago, the pop-off opened while we were under
Jim,
A standard T&P on a water heater is set at 210F and 150 psi. There are
175psi T&P valves available, don't use them on ANY water heater, the
standard tank is rated 150 psi. The purpose of the valve is to keep the
pressure vessel, the water heater - from becoming a bomb if the contents
exceed flash point. The likelihood of creating that condition with just
engine coolant heating is slim, but conceivable in theory, however
entirely possible with a runaway electric heating element. When the
valve opens, the pressure drops, plus cooler water flows into the tank,
helping to mitigate the condition that caused it to open in the 1st place.
If your T&P opened, replace it. They're not expensive, and if it opened
and did not close completely, it's compromised, and should no longer be
considered functional safety device. Shutting off the pump may be
effective, but IMO is bypassing the real solution to the problem.
Just reiterate, the T&P valve differentiates between pressure vessel &
bomb. Water at pressure and temperatures that approach the flash
(boiling) point is not something to be trifled with. Any T&P valve that
exhibits any questionable condition should be REPLACED.
steve sipe
Solo 4303 "Maerin"
tonight - 7 Seas Marina Port Orange
On 1/8/2010 9:09 AM, Jim Healy wrote:
> A little off the point of contaminated potable water, but hopefully of
> interest. We run with our house water pump turned off all the time, every
> time. It's part of our pre-departure checklist. The reason is that the hot
> water tank, an Atwood, has a safety pressure relief (pop-off) valve on it that
> is pre-set at 185 degrees. When the engine is running, the engine coolant is
> in that temp range. Several years ago, the pop-off opened while we were under
>
Jim,
A standard T&P on a water heater is set at 210F and 150 psi. There are
175psi T&P valves available, don't use them on ANY water heater, the
standard tank is rated 150 psi. The purpose of the valve is to keep the
pressure vessel, the water heater - from becoming a bomb if the contents
exceed flash point. The likelihood of creating that condition with just
engine coolant heating is slim, but conceivable in theory, however
entirely possible with a runaway electric heating element. When the
valve opens, the pressure drops, plus cooler water flows into the tank,
helping to mitigate the condition that caused it to open in the 1st place.
If your T&P opened, replace it. They're not expensive, and if it opened
and did not close completely, it's compromised, and should no longer be
considered functional safety device. Shutting off the pump may be
effective, but IMO is bypassing the real solution to the problem.
Just reiterate, the T&P valve differentiates between pressure vessel &
bomb. Water at pressure and temperatures that approach the flash
(boiling) point is not something to be trifled with. Any T&P valve that
exhibits any questionable condition should be REPLACED.
steve sipe
Solo 4303 "Maerin"
tonight - 7 Seas Marina Port Orange
