"Dave Hinz" wrote in message
...
On Wed, 21 Sep 2005 15:07:18 -0400, Jeff Wisnia
wrote:
Dave Hinz wrote:

Exactly. Most hydrants over the last (insert bignum) years have
the
shutoff valve on a long temp which goes well underground - prevents
freezing in that sort of climate. So the hydrant is dry for maybe
(thinks) 6 feet of height at a 8" diameter. So, it's compressed to
50PSI (or whatever mains pressure is) once that valve is opened,
which
is quite a bit of force on a 6" hose connection.

My inquiring mind just had to know...
How does the water drain out and the air get back in when it's time
to
close up and go back to the station?

That's a good question. Unfortunately the hydrants I have (long
story,
don't ask) are missing that end of the mechanism. I would assume
there
is some sort of a drain.

Sure enough, there's a drain valve at the bottom of the hydrant
which
opens when the main water valve is closed. I expect they must put
some
crushed stone around the bottom to give the water someplace place to
go.

Oh good, you saved me a trip to google. Makes sense.

This picture shows a hydrant with an automatic drain valve:

http://empire-west.com/iowa_parts_list.htm

That hydrant looks like it uses a toggle action driven by right/left
threads on the valve stem to move the main valve sideways. Clever...

The ones I have just move the rod up/down, but they're ancient.

I wonder if they have to leave the cap off until they are sure the
water
has drained out to avoid creating an air lock?

Dunno. We don't have hydrants in our department's area, our parties
are strictly "BYOW".

Dave Hinz


Same thing with us. Do get lucky sometimes and find a pond or pool with
some wet stuff in it. We do have one are that has hydrants BUT those are
ornamental for water flow since they were installed in the mid 40's and
have a HUGE 3" mainline, which with the mineral content in the water has
shrunk to about 1", They are also connected into many private wells and
if you did hook to them you are in for a BIG surprise. We had that
happen back in the 60's when they tried connecting a small pumper to one
as a test. They couldn't get enough water to keep the pump primed.

Steve W.



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