Help me send water up the wall
June 5, 2013 6:29 AM   Subscribe

This evening I'll be installing a new drip irrigation system for our garden. I've got vegetables down low, plus some planted on top of an 8-foot retaining wall, and I'm wondering if the system will work.

It's the basic 1/2" and 1/4" tubing, plus drippers, as well as (at the faucet-end) a timer, backflow preventer, filter, pressure regulator, and maybe some other adapters or doo-dads. My plan is to run a single line of 1/2" tubing along the ground, sending out 1/4" lines into the garden bed, plus a 1/4" line for the herb pots, another for some tomatoes in buckets, and (here's where it gets tricky) another straight up the wall and along the top, to water a pair of pumpkins and a cucumber that are planted up there.

I don't know anything about fluid dynamics. Half of my brain is telling me that there will be more than enough pressure in the lines to push 1/4" of water up a few feet. The other half is telling me that I'm an idiot and it's all going to drip out the lower drippers. What can I do to make sure this system works?
posted by sleevener to Home & Garden (7 answers total) 1 user marked this as a favorite
Best answer: I've done a bit of drip irrigation in my home garden, mostly flat but with one branch going up to a window box about five feet off the ground, and that wasn't a problem. I think the worst that might happen is that pressure is lower up on top of the wall, so those plants might get less water. You could compensate by using higher-capacity emitters up there.
posted by jon1270 at 6:46 AM on June 5, 2013

Best answer: In a similar situation, I ran two 1/2" lines: 1 for the upper wall, 1 for the beds on the ground. I have pretty low water pressure, so this was the only way I could get water up to the upper bed. The total number of 1/4" lines tapping off each 1/2" line will determine your water flow, too. Take a look a for some good videos on planning a drip system.
posted by summerstorm at 6:56 AM on June 5, 2013

I don't know if this is feasible with your layout, but can you put in a valve that shuts off everything except the wall line? This would solve the problem of all the pressure going to the low spots. If you can put it all to the one line you might have a better shot.
posted by silvergoat at 8:56 AM on June 5, 2013

Best answer: Static water pressure is related to height. For every foot, you gain 0.433 PSI of pressure at the bottom. So, ignoring the effects of flow (ie: too many drippers on a ¼" hose) if you have a 15 PSI regulator at your valve, a foot below your valve (where that hose runs along the ground) you'll have 15.433 PSI, and on the top of a wall 8' above that regulator you'll have 11½ PSI.

(If I remember right, house water pressures run from about 35PSI to 90PSI, my house is on the high end.)

I thought that drip pressure regulators were 15PSI, but looking around I'm seeing that they seem to be 20-30PSI, so these differences are even less pronounced as a function of overall pressure, but...

If you're worried about this difference (I wouldn't be for an 8-10' wall, but maybe you've got more rise?): Put the valve and anti-siphon backflow preventer at the faucet, then T the lines, and put a pressure regulator on the line at the ground and another one up on the top of the wall.

From a practical standpoint: We have a valve and pressure regulator at ground level, and then run up to a living roof that peaks out about 13' above the pressure regulator. Of course all of that run is at the same level, so we've just adjusted the entire zone to saturate that soil, but I'd actually not thought about the effects of pressure drop in that run before.
posted by straw at 9:08 AM on June 5, 2013 [1 favorite]

Including a small submersible pump or small aquarium flow filter might help with any pressure problems that come up.

Some ideas for how to do that here and here.
posted by misha at 9:11 AM on June 5, 2013

Response by poster: Thanks, everyone, especially for the reassurance! I'll check back in with photos of withered baby pumpkin plants if everything doesn't go as planned.
posted by sleevener at 12:09 PM on June 5, 2013

Response by poster: Update: the system works as planned -- the upstairs vine plants are never thirsty. Thanks again for the help, all.
posted by sleevener at 8:07 AM on July 10, 2013 [1 favorite]

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