"Doctor Drivel" wrote in message
reenews.net...

"daestrom" wrote in message
...

wrote in message
oups.com...
Doctor Drivel wrote:
wrote in message

simpler to have the vent hole above the top of the tank. Add a sleeve
to prevent splash possibility.

It has to be "in" the tank. The pump will squirt water everywhere.

What I'm suggesting is a 1/4" hole in the panel output pipe just above
the top of tank, say 1/2" above. There will be close to no pressure
there, and no possibility of any squirting.


Okay, and if there is no check-valve in the pump or its suction, I can
see that working. Maybe even a baffle just to be sure of little splash.
Shut-off head of the pump will still have to be high enough to initially
fill the collector, but once the return has flooded, less pressure should
be needed to maintain flow.

Now, just need a large enough tank to accomodate the drain-water, and
you're all set.

Although it would take three pipes. A foolproof way is have a tee inside
the tank on the hot pipe from the panels. From this tee take a small bore
pipe up to the same height as the top of the panel and back to the tank.
Vented and no pump over at all. If there is a problem it goes back to the
tank. Pipe is cheap.

Why go all the way up to the panel height? If you make sure the hole is
always above the water level in the tank, and put a small enough
orifice/restriction in the hole, the flow of water out the hole will be
minimal. With the pump off, the difference between where the hole is and
the water level in the tank will start the reverse syphon process. As water
syphons backwards through the collector and pump, the return line will be
more and more air (less and less water) so the dP for the syphon grows and
grows. Soon the whole pipe and collector will be drained.

Things that can go wrong: 1) If there are any low spots that don't slope
back to the tank, they may hold water that can then freeze. 2) Some fool
puts a check valve in the line. 3) If the orifice/restriction/hole gets
clogged with scale/crud/biofouling, then the system may not drain. The
first two are avoided by careful installation. The last, increase the
height above the water line for the hole to provide a stronger dP for
clearing the crud. Heck, maybe rig a circuit that if the pump is running
but no water out the hole after 60 seconds, sound an alarm. Scale could be
prevented with a simple mechanical reamer every 3 months or so.

But running a pipe all the way up to panel and pack down creates a
'loop-seal' that will *prevent* drain down, exactly the wrong thing. Now
you have to 'upside-down U' sections of piping to break the syphon seal on
both to prevent freezing.

daestrom