more gardening: soaker hose

[tbn.al]

You can get rubber washers of varying strengths to put in the hose end connector to get the pressure to whatever you want. Each of my soakers came with a set of 3 different washers. I also bought some hose in a hundred foot roll once from Home Depot, I think, that lasted 3 or 4 years.

[Uncle Buck]

I think I am going to try your idea in the areas where I use soaker hoses.

In terms of water pressure, I don't know any way to know for certain without just trying it. Too many variables for me to try to calculate (although you don't have to worry about things like all your neighbors deciding to water at the same time . . .)

[Rick Denney]

(By the way, I have used the black soaker hoses that are continuously porous. The black is carbon black, which resists UV. I watered the foundation of my house in Dallas with several of those for about five years, and never had a failure.)

Water is incompressible. That means that what goes in comes out, and it does so at the same time. Air-conditioning duct-work has size reductions to control flow, but that's because air is compressible. Water pipes are sized for the fixtures at the downstream end to supply sufficient flow at usable pressure.

The basic design principle is that those fixtures should supply the constraint on flow, so that pressure is kept positive in the feed hose/pipe.

100 feet of 1/2" PVC pipe will drop the pressure 4-10 psi or so if you stay below the maximum recommended 5 feet/second velocity. At that velocity, 100 feet of 5/8" feed hose will also cause about a 7 psi drop. That's a total pressure drop of 10 or 15 psi, and you should be able to supply at least 40 psi, which is typical for residential well systems. The pressure drop entirely depends on flow, because friction is zero at zero velocity (when pressure is high) and highest and velocity is highest (when pressure drops). You are talking about a low-velocity system, otherwise you'll be spraying not soaking, so pressure will be constrained to be high so that you can keep the velocity down.

Now, let's consider flow requirements. Let's aim for 4 gallons/minute at dribble pressure, and then check to make sure the above can deliver it. For open-channel flow, which means water will fall out of those holes instead of spraying out of them, Q = VA, where Q is flow, V is velocity, and A is area. A flow of 4 gallons/minute is 15.4 cubic inches per second. If velocity is 60 in/sec, you need about 0.256 square inches of area to allow that flow at dribble (zero) pressure. If you put 100 holes in the pipe, you need holes of 0.0571" in diameter.

But maintaining zero pressure will cause problems for you. To get the dribble, you need a pressure regulator at each one of those holes that will limit flow and maintain pressure in the pipe. That's the only way you'll get even velocity (and therefore flow) out of each hole. There is nothing easy you can do with pipe sizes to prevent that--restrictions limit velocity and then flow, and build upstream pressure, so even slight changes in pressure would change the way those holes spray dramatically. And at such low velocities, keeping pressure zero means very low flow. You'd have to design restrictions based on the change in pressure (head) resulting from slope, and I think you'd spend the rest of your life figuring it out. And then it would be wrong if you changed the setting on the hose valve just a little. If the pipe is dead level, what I've suggested above will work.

You'd have to regulate a dead level pipe to 4 gallons/minute at the source, and then the psi drop in the hose and pipe might only be 14 psi if it were unconstrained on the end. Thus, your holes will flow more than your pipe to get your flow target. A change in pressure of only 1 psi is lilke a change in elevation across the length of the pipe of 28 inches. It's just too sensitive.

I think you need to spend just a little of that stash and look into a drip irrigation system. These work using flow-regulating drippers so that the pressure in the hose can be kept high. They use a flexible diaphragm so that the higher pressure, the more it controls flow to keep the flow the same. They are easy to use, too. They use a larger cross-linked polyethylene tubing (far more durable than garden hose). You insert puncture fittings, attach small tubes to those fitting, and then put the dripper at the end of that tube. The dripper sits right next to the plant.

I installed one of these to irrigate a 4000-square-foot patch of 100 newly planted Blue-Rug junipers at my previous house. A single garden hose provided drip irrigation to all 100 plants evenly, and the patch was on a steep 1:4 slope. The cost was not that high, else I wouldn't have done it. Looking now at the first mailorder site that comes up on a Google search, the main tubing is about 10 bucks for 100 feet, and the drippers are 3 or 4 for a dollar.

Rick "drip flow velocity is too slow to easily regulate pressure" Denney

[ralphbsz]

Tried the "drilling holes" thing. Nearly impossible. The size hole you need is TINY; I was going at the pipe with a #72 drill bit, and breaking drill bits faster than the police allows. If you use larger holes (like 3/32, which is a sturdy drill bit that you can use in a drill press), you don't have a soaker pipe, you have a giant leak.

Tried the black porous pipe (it looks like it is made out of a highly compressed sponge). It works, but only for a few weeks. Our gardening water is extremely hard, and the porous pipe clogged. I tried fixing it by stuffing it in a bucket and pouring diluted muriatic acid over it, but that caused the hose to fall apart.

We still occasionally use 1/2" poly pipe (black flexible), then punch holes in it every foot or two, and install drip emitters (usually on a short extension using 1/4" pipe). This lasts for several months without requiring service. If you do maintenance on it (opening and flushing the drip emitters) every month or so, and repair anything that breaks (the little 1/4" pipe tears off when someone trips over it, or rodents eat holes into it), then it lasts for years.

The only thing I trust is real sprinklers. Either Toro or Rainbird heads. Ideally, you feed them from buried PVC pipe. That will last for a long time, and only requires a tiny bit of maintenance (once or twice a year, look for clogged or broken sprinkler hears). But what is much less work is to instal the heads above ground (just duct tape them to cheap stakes, like small metal fence posts), and feed them using 1/2" or 3/4" black flexible poly pipe and tee's. Requires some regular service, but not much. The larger the area to be sprinkled, the better. If you have a large enough area to use 3/4" impact sprinklers (the brass things that go adagio tok-tok-tok in 1/4 notes, the return by tok-tok'ing 16th notes), then installation is not much of a problem.