On Sep 29, 1:30*am, blueman wrote:
Just wanted to describe a circuit I built to automate blowing out a
multi-zone irrigation system using a small home compressor. But first
let me give some background.

For the past 5 years, I have successfully blown out my irrigation
system each fall using a 10 gallon compressor that I bought for $99
from Home Depot (and that therefore paid for itself the first year
that I didn't need to hire a service).

Until this year, I have used the following painstaking manual
process. Specifically, for each of the nine zones on my system, I have
let the compressor fill & empty about 6 times waiting about 4 minutes
between attempts so as to keep the duty cycle down and prevent the
compressor from overheating (I also aim a small fan at the compressor
fins to further aid cooling). *The multiple times per zone is required
since 10 gallons of air is not sufficient to blow out all the
tubing. The visible water is blown out within the first 2-3 cycles and
I add another 3 cycles or so just to be sure and to get out the last
drops that show up as a light mist. This painstaking process, however,
requires me running back and forth to my garage about 54 times and
wastes the better part of a day. *Last year, I was able to save some
time by "cleverly" programming and rewiring my controller so that
every other zone was disconnected, allowing the compressor to recharge
on the intervening disconnected zones - this reduced my manual
interventions to about 12 trips to the garage.

This year, I built a simple circuit based around a 555 timer and a
relay that runs off the 28VAC transformer (using a bridge rectifier,
regulator and capacitors to reduce and convert the voltage to
12VDC). The timer turns the relay on for 1 minute and then off for 4
minutes (though both times are adjustable with a pair of
potentiometers). Two leads connect to the VAC and the other two leads
go across the rain sensor terminals (with the rain sensor temporarily
disconnected). Then I can automatically blow out the whole system by
setting my irrigation controller to run sequentially through all nine
zones with 30 minutes or so per zone (which gets me 6 cycles per
zone).

If anybody is interested in the schematic, I would be happy to share
it along with photos of the completed project. Note I also added two
LED's (red & green) to show the relay state, an off/switch, and a nice
box to package it all up.


Very creative solution. I've been doing mine with an old Sears
compressor, maybe 15 gallon size. So, I know exactly the issues you
are having. Mine isn't too bad, only 7 zones with 3 heads a zone.
Controller is in the garage and blow out connection is outside the
garage, maybe a 40ft walk.

Last year, I helped a friend do his using my compressor and the
problems were even worse. More zones, more heads per zone and the
controller is in the basement. One thing I like about your solution
is you can set it up so it takes it's time and the compressor gets to
rest. Without being able to automate it, I would not do his again.
It was far too taxing on both me and the compressor.

If its easy for you to send the schematics I'd appreciate them. I
might decide to build it.