Berkshire Bill wrote:
Check this out to really appreciate pressure relif valves.

http://www.waterheaterblast.com/

http://seattlepi.nwsource.com/local/33094_boom28.shtml


Bill

uh... how does a piece of pvc prevent what is described in your
articles?

and I quote:
"Water heaters are equipped with pressure-relief valves -- typically
placed on the top of the heat. The valves are designed to open
immediately to relieve pressure if steam builds up in the heaters.

Although rare, pressure explosions of water heaters do occur.

In 1993, for example, a 40-year-old water heater exploded in a home in
South St. Paul, Minn. The 200-pound tank shot through a floor, ceiling
and roof like a missile.

The explosion shot the heater 150 feet in the air. It destroyed the
home, slightly injured two people and killed the family beagle."

And the link to the picture is from a promo video for the relief
device...it's from the 30's IIRC, I've seen it on TV a few times.
Very old video.