Dealing with air trapped in a gravity fed drip irrigation system.

Sometimes I feel like I'm the only person actually using gravity fed drip irrigation.  There just isn't a whole lot of information available about it on the Internet.  What I do find all says the same thing.

• Raise the height of your water source as much as possible to increase pressure.
• Keep your drip lines short.

I didn't keep my drip lines short.  I'm using hundreds of feet of drip tubing.  Also, I'm real leery of raising a ~500 lbs. barrel of water real high in the air.  Theoretically it could be done, but whatever is holding would have to be real sturdy.  I want to take the chance of that kind of weight falling.

Anyway, I've noticed recently that some of my drip emitters are flowing real fast and some don't appear to drip at all.  When I pull the cap off of the emitter it gurgles and bubbles indicating that there is air trapped in the line.  I had this issue once before.  I installed a vertical tube to allow the air in the system to escape.  That worked for a while.  Then I added more raised beds, added more drip lines, and extended the lines in the existing beds.  All of that means a lot more emitters.  That single vertical line isn't sufficient for removing all of the air in the system.

My solution was to add more vertical lines at various places.   On the first two beds I ran the vertical lines off of the main trunk to allow the air to escape before entering the branch lines in the beds.  I made sure the lines were higher than my rain barrels.  That way it won't ever overflow (water always finds its own level).

Vertical line allows air to escape before going into the branch line in the bed.

Vertical line allows air to escape before going into the branch line in the bed.

On the next two beds I simply extended the branch lines and ran them vertically.  My theory here is that the air will be pushed through the line to the end and escape.

Drip irrigation line run vertically allows air to escape.

Drip irrigation line run vertically allows air to escape.

The changes I made above made a huge difference.  All of the emitters in every bed seem to work just fine.  I haven't noticed any more air trapped in the lines.  Of course the question is, "Is it better to run the vertical line at the end of the branch, or put the T in at the beginning?"  I didn't do any careful scientific experimentation to determine that, but from a purely practical point of view, extending the line is easier.  It requires fewer fittings.  It wouldn't require any at all if you planned ahead.  I only needed them because I had to couple a new line to the old.