Rob Robillard, editor at http://www.AConcordCarpetner.com explains how to blow out your irrigation system
The blow out method utilizes an air compressor with a 800 to 100 Cubic Foot per Minute (CFM) rating. My compressor has a 33 gallon tank and is perfect for my large 6-zone system. My neighbor uses a 6-gallon compressor for his small 2-zone system. Either compressor is fine for a system that has a water mainline of 2-inches or less. My system as a 1-inch mainline.
Location of Connection
If possible try to locate your air hose connections after the PVB back-flow device as compressed air can damage the PVB back-flow device.
A pressure vacuum breaker is used on irrigation systems to protect water supplies from contamination or pollution.
Irrigation back-flow devices are designed for installation on potable water lines to protect against both back siphonage and back pressure of contaminated water into the potable water supply.
Two Compressor Attachments
To minimize the risk of freeze damage, you’ll need to winterize your irrigation system blowing air through the pipes to push all of the water out of the lines. The compressor attaches to the
For short money you can make your own attachment to connect to your irrigation system.
The simplest connections is to use a quick coupler that will work with your compressor an a threaded, double ended connector. These two components can be combined and inserted in the the threaded portion [wrench required] of the test cocks on the Pressure Vacuum Breaker.
Another method that does not require a wrench is to make a hose bib or sill cock connector. I made mine with an old washing machine hose that I cut down to 18-inches. I then bought a quick coupling and a threaded to barbed connector to join my coupling to the hose. A small “water pump type” clamp holds it together. This assembly is simply screwed onto the existing hose bib.
The first step is to shut off the irrigation water supply. Typically this shut off is near the main water meter entering the house. You may have to trace the pipe back fro the PVB to locate the shut off ball valve or other valve.
After the water is shut off, you should drain the inside water line. Most systems, have a drain plug, or sill cock drain to drain and dry the water line. I open this valve and drain the pipe into a small bucket. Water will come out but in order to completely drain this line, you will need to open either the sill cock valve or a test cock on the PVB [house side] to allow the pipe to completely drain.
Once this pipe is drained go outside and close the back-flow isolation valves to isolate the water supply line to house. Open and drain the test cocks on the PVB
Using your connectors attach your compressor to the system [irrigation system side of PVB] to either a sill cock or a test cock, depending on your system. Keep the valve in the closed position, as you attach the air compressor hose to the fitting. It is important not to run a compressor without an open valve, as the compressed air can damage a zone valve gate
The next step is to turn on and activate the sprinkler zone station on the controller. Turn on the zone that is highest in elevation and the furthest from the compressor.
Slowly open the valve on the compressor; to allow air into the irrigation system. With a hose bib connection you simple open the sill cock / hose bib valve. With a quick coupling connection at a test cock you can use the test cock valve and a screw driver or turn the isolation ball valve to control the air flow.
The rule of thumb is to let the air run through each zone for 2-minutes. I typically do a minute or less and repeat after the compressor has had time to recover and charge up the tank.
Each station/zone should be activated until no water can be seen exiting the heads, I suggest that you repeat the whole process a few times to ensure the maximum amount of water has been evacuated from the system. With smaller compressors this may take longer.
After the water has been evacuated from the irrigation lines, disconnect the air compressor and release any air pressure that may be present in the lines. Then open and drain the all of test cocks again on the PVB to ensure water has drained.
The final step is to open and close the isolation ball valves on the PVB back-flow device a few times to ensure that any trapped water has escaped from the upper areas. Finally, turn and leave these valves at a 45˚ angle,