Don Y wrote:
On 11/23/2015 10:39 AM, Bob F wrote:
Don Y wrote:
On 11/22/2015 2:17 PM, Retired wrote:
On 11/22/15 4:04 PM, Don Y wrote:
We have reasonably hard water -- municipal well sourced along with
CAP.

I've plumbed the "outdoor water supplies" (i.e., irrigation and
hose bibbs) to use water directly from the municipal supply
(i.e., NOT "locally" treated) as I don't want to be paying to
"treat" water that's going out a garden hose, etc.

[I don't think the plants would like the extra salt, regardless]

There are ~20 solenoid operated valves buried around the yard
(little concrete, covered vaults that I built for them). Each
operates an irrigation "zone" *or* one of the 4 hose bibbs
scattered around the perimeter.

The irrigation *lines* are all below grade. So, essentially safe
from freezes. But, the hose bibbs require the water supply
(exiting the solenoid valve) to climb to a height that is
convenient for a human user to access. So, that portion of
the plumbing that is above grade is exposed to the elements
more than the rest of the lines which remain below grade.

These risers are 3/4" copper run through the "voids" in 8"
"half (cinder) blocks" which have then been filled with
"Nasty Foam" (TmReg) to improve insulation.

So, you have a length of copper pipe that exits the solenoid
valve, rises through the surface of the soil *into* this
foam-filled void and terminates at a hose bibb -- the valve of which might
be
open or closed

[no idea as to which; the whole point of the solenoid is to allow
me to put a garden hose on a bibb, set the (manual) valve to an
appropriate flow rate, and direct the hose's output to a
particular spot in the yard that needs "supplemental watering".
Then, use the solenoid to turn that water supply on or off.]

Of course, I don't want to risk the water standing in that pipe
freezing and rupturing the pipe (I can't rely on it destroying
the valve, instead : ).

To that end, I installed these auto-drain valves (colloquially
known as "spitters") on the "load" side of the solenoid.
They resemble a PCV valve in construction: an opening which
can be plugged by a slug of metal inside the valve body.
A low tension spring holds the plug AWAY from the opening
so it is normally open. The slightest water pressure acts
to push the slug (plug) against the hole thereby sealing it.

When pressure is removed, the spring's force eventually
overcomes that of the fading water pressure and the slug
exposes the opening. As this is located at the low point
in the plumbing, the water "standing" above it *should*
drain out through this opening.

[This is a sort of *******ization of their use]

Over time, I suspect these will fail due to concretions
from the water supply. Anyone know for a fact if this is
true? I've located them in a way that allows me to
service them down the road. But, I'm looking for FEWER
chores, not MORE! :

Alternatively, I'm considering forcing all of the solenoids
*open* (after turning off the main supply) and hoping water
will "seek its level" throughout the system -- instead of
dealing with each of these little "stand pipes" in isolation.

[Or, even adding an "extra" valve whose sole purpose is to be
the "low point" in the system so there is a place BELOW GRADE
for all water to drain]

Is blowing the lines out with compressed air not feasible for some
reason ?

How would I do that? This is intended for "unattended operation".
E.g., today, irrigation zones 3, 7, 8 and 14 might be used --
individually or in some combination. Tomorrow, hose bibb #2 might
see some use and the *solenoid* for bibb #4 might be engaged --
but, someone may
have turned off the (manual) valve/bibb (because they decided this
supplemental water was no longer needed yet hadn't got 'round to
updating the "programmed watering schedule", yet).

So, if I force air through from the *supply*, there's no guarantee
it will have a means of "exit" (assuming I deliberately open all
desired solenoids).

You apply the air pressure from the source end, then cycle through
the valves, opening each until you get mostly air from the
sprinklers on that valve. I've heard a fairly large air supply is
best for this. I use my 5HP compressor.

That seems even more problematic! Now I need a way of
(electronically) disconnecting the water supply line from the
"outdoor distribution system" and connecting an air supply in its
place. Then, a means of ensuring the air pressure never exceeds the
working limits of the plastic and copper pipe and other fixtures in
the outdoor system. A way of applying that pressure and knowing when it's done
it's trick.

What do I do if the hose bibbs are closed? Where does the water
"standing" in the riser pipe go? If I open the solenoid valve and it
manages to drain down "backwards, through the solenoid valve to
come to rest "below grade", how is the air pressure going to force
it through the CLOSED hose bibb??

I.e., you need a means of creating an "exit point" -- like these
"spitters" -- if you want the water to leave the system.
(If it just "runs backwards" then you're doing nothing special
with the air supply that wouldn't happen in its absence!)

[I'm not sure the "standing" water will flow back down without
a means for air to displace it from above. I'm sure there's
a formula for water surface tension vs. gravity someplace
that would indicate how large a dia would be required for the
water to "fall" from its own weight. Imagine water in a
soda straw with the top end pinched shut. It's not going
to "fall back down" without "encouragement"]

The whole point of all this is to be able to have it all happen
"unattended". E.g., if my gizmo notices that "conditions are
appropriate" to supply water through the hose bibb or irrigation
valve in question, *it* should be able to do so AND RETURN THE
HYDRAULICS TO A SAFE STATE (without fear of freezes, etc.)

But, *it* can't physically turn the "knob"/faucet on the hose
bibb to ensure that MECHANICAL valve is open when it needs
for it to be!

"Um, Don... can you please get up and open the valve on
hose bibb #3 so I can drain the lines FOR you?"

You like it complicated. I just drain everything when I shut it down for winter.
It's not likely to freeze any other time.

Your auto drain valves won't do what you want unless there are leaks somewhere.
As long as there is pressure, they won't open. A sprinkler head relieves the
pressure, but a closed faucet won't. You have to shut off the water, and open
the faucets for it to work right. The drains may not work right without air
being able to get in somewhere while the water drains out too.

Good luck.