The “Blow Out” Method with an Air Compressor
The blow out method utilizes an air compressor with a Cubic Foot per Minute (CFM) rating of 80-100 for any mainline of 2″ or less. These types of compressors can be rented or purchased at Central Turf & Irrigation Supply. The compressor is attached to the mainline via a quick coupler, hose bib or other type connection, which is located after the backflow device. Compressed air should not be blown through any backflow device. To start the “blow out”, shut off the irrigation water supply and, with the compressor valve in the closed position, attach the air compressor hose to the fitting. Activate the station on the controller that is the zone or sprinklers highest in elevation and the furthest from the compressor. Close the backflow isolation valves. Then slowly open the valve on the compressor; this should gradually introduce air into the irrigation system. The blow out pressure should remain below the maximum operating pressure specification of the lowest pressure rated component on that zone and should NEVER exceed 80 PSI.
Each station/zone should be activated starting from the furthest station/zone from the compressor slowly working your way to the closest station/zone to the compressor. Each station/zone should be activated until no water can be seen exiting the heads, this should take approximately two minutes or more per station/zone. It is better to use two or three short cycles per station/zone than to have one long cycle. Once the station/zone is dry, you should not continue to blow air through the pipe. Compressed air moving through dry pipes can cause friction, which will create heat and the heat could cause damage.
WARNING! WEAR ANSI APPROVED SAFETY EYE PROTECTION! Extreme care must always be taken when blowing out the system with compressed air. Compressed air can cause serious injury, including serious eye injury, from flying debris. Always wear ANSI approved safety eye protection and do not stand over any irrigation components (pipes, sprinklers and valves) during air blow out. SERIOUS PERSONAL INJURY MAY RESULT IF YOU DO NOT PROCEED AS RECOMMENDED!
Once the water has been removed from the irrigation system, disconnect the air compressor and release any air pressure that may be present. If your backflow device, the most common backflow installed is called a Pressure Vacuum Breaker, has ball valves, open and close the isolation valves on the backflow device numerous times to ensure that any trapped water has escaped from the upper areas. Leave the isolation valves open at a 45° angle (approximately 1/2 open) and open the test cocks.
Preparing a hydraulic control system? Shut off the water supply to the signal control tube(s) and drain the field tubing.
Outdoor mounted controllers? Leave the power on and the dial / switch in the “Off” position. The heat from the transformer will keep the enclosure warm enough to keep condensation from forming inside the controller enclosure. The dial in the “OFF” will keep the controller from activating the solenoids in the field.
For Indoor Mounted Controllers
You may either leave the power on and the dial/switch in the “Off” position OR you may remove the battery backup and unplug the transformer.
For Rain Sensors
There is not much to do to prepare the rain sensor for the winter months. If your sensor is the type with a cup or bowl that catches water, you might want to remove the water and place a plastic bag over the sensor. This will keep any water from accumulating and freezing in the cup or bowl area. If your sensor is the type that uses wafers or discs, you might want to remove the wafers and store them in the garage for the winter months. This will keep damp wafers from freezing.
Don’ts of “Blow Out” Winterization
Don’t allow the air pressure to exceed 80 PSI for PVC systems and 50 PSI for polyethylene systems.
Don’t stand over component parts while the system is pressurized with air.
Don’t leave the air compressor unattended.
Don’t blow the system out through a backflow or pump. First blow out the system, then drain the backflow or pump.
Don’t leave the manual drain valves open after the blow out.