pressure drop per foot of tubing at different flow rates.

Everett, WA(Zone 8a)

Does anyone know where to find olf table of pressure drop per foot of tubing at different flow rates?

I often see "max practical flow rates" quoted for different size tubes, but that must mean that, around that flow rate, the pressure drop per foot becomes serious.

I'd like to be able to estimate how much the pressure drops along the line in (say) 1/4" OD tubing when the total flow approachs 30 GPH. And I might plan on having lower pressures at the far end, by putting spot spitters at the far end where they don't need much pressure.

These "max practical flow" numbers are from memory.

3/4" PE Mainline - - 0.830" ID - - 480 GPH

1/2" PE Mainline - - 0.600" ID - - - 240 GPH

1/4" PE micro tube - 0.170" ID - - - 30 GPH

1/4" Vinyl or
PE 'Rigid Riser' - - - 0.160" ID - - - - 30 GPH ??

1/8" PE micro tube - 0.125 ID - - - - - ?? 12-20 GPH??

Then I also wonder whether the flow numbers they quote allow for the fact the the openings in transfer barbs are much smaller than the tubing ID!

Everett, WA(Zone 8a)

I found one site that gives overall results for a certain inside diamter, tube length and flow rate.

But you have tio know how smooth your tube is. I wonder what the surface smoothness of extruded Polyethylene is?

Everett, WA(Zone 8a)

I guess not many people are interested in fluid dynamics!

I like "Shrubblers" because they are adjustable and throw water only a few feet, UNDER the leaf canopy.
I WOULD like variable-flow sprayers with built-in valves, except they seem very fragile.

I like 1/4" dripline because it puts water ONLY where I want it.
But it has a low flow rate so you have to leave it turned on for longer than sprinklers or sprayers.
I like the 6" spacing because 12" spacing just waters small, disconnected dots of soil.
But " tubing only supports ~30 GPH, so you need short runs or the pressure drops before it reaches the end of the line.

Hose Fittings Give Flexible Options

I like to provide a lot of "hose fittings" on my mainline. They have to start with a "female hose beginning" to mate to the faucet. I end m y lines with a "male hose end" with cap. Then I can always add a short length of garden hose with a water-breaker wand or sprayer. Also, I can come back later and extend the mainline or convert it to 1/2" tubing by attaching a female hose beginning to the second length of tubing.

And I can cut into my 3/4" mainline at any point by splicing in a Tee with two 3/4 compression or easy-lock ends, and one male hose end. Then I can attach anything to the male hose end.

I especially like attaching a hose "Y" with two valves. The female end of the Y screws into the male hose end on the Tee. Now I have TWO male hose ends with VALVES. So I have good flow control for the two branches. I already find that I want to stop watering some zones sooner than other zones, because I have not yet gotten the right flow volume fittings for each zone.

Also, these hose-flow-valves let me throttle or fine-tune the flow rates to different areas, so I can reduce the pressure to some sprayer or sprinkler so it won't throw water as far. (Also, at low enough pressure, a mist-like sprayer starts spitting droplets that waste less water to evaporation or misses.)

Inserting Barbs

I'm about to invest in a tool for shoving the barb fittings into 1/4" tubing, because my fingers get tired & blistered!

Alternatively, I make a pot of hot water with my Mr. Coffee machine, then dip just the TIP of the tubing into it. I also have a metal spike with a very gradual taper, polished smooth. I push that into the 1/4" tubing to stretch it a little, dip in hot water, push again, pause to let it stretch, then pull out the spike and quickly force the barb into the tube.

10/32 threads do NOT hold 1/4" tubing well enough to contain 45 PSI. POP - then a 40 GPH fountain. You have to use the barb to hold in 1/4" tubing at that pressure. So I will buy a 30 PSI regulator. And I might get a 20 PSI regulator orf lower, so I can use a spray jet designed to throw water 8 feet, on an area only 4 feet wide.

A trick: 10/32 threads WILL hold 45 PSI if screwed into "Rigid Riser", a special thick-wall 1/4" tube. In inch or two of Rigid Riser with 10/32 threads going into the RR and a 1/4" barb on the other end will let you scrfew it on and off if needed, yet hold regular 1/4" tubing on the barbs.

Fremont, NE(Zone 5b)

We own a underground sprinkler business and I install the drip systems for landscaping.
The tool you are talking about is worth its weight in gold after pushing in quite a few emitters by hand..Ouch !!!

You where talking about pressure drops. I normally install Rainbird 1/2 drip tubing with 12" spaced emitters that are pressure regulating and then I tap off of the 1/2" pipe for plants that are off set and for pots and hanging baskets. I find on long runs it is best to loop sections if possible and if that is not possible I will run another main line about midway through the drip system or connect to other end to keep a good flow of water.
The 12" spaced drip line puts down not quite an gallon per depending on watering needs a person just waters accordingly. The water does not just stay in spots but depending on how long you run it, it should water 12" around each emitter.

Your drip system will work better at a lower psi, 45 psi is on the high want it more around 30. However I would be careful to not lower the pressure too far if you are trying to use the micro sprays as they may not work as well, especially if you are T'ing off the 1/4 tubing and adding several micro sprays onto one can run into trouble there. For example if you have 45 psi you can run several micro spays to one 1/4 tube but say on another run you only need a you end up blowing them off...where as they worked on the other run because you where asking for more water. But if you already have it set up and lower your PSI too far
the runs with several sprays are not going to work..So it is best to run a mid range PSI..the runs with several sprays will work and hopefully you will not blow off the others.
Sometimes it can be a bit of a trial and error until you find what works best.

On my own system at home..I have horrible PSI and water flow. I can only run one micro spray per 1/4 tube. So I have blank 1/2" tubing and plug 1/4" barb connectors into the blank tube so I can run 1/4 tube to each micro spray.
Actually my system has been in for sometime prior to the drip line coming out, If I can ever find the time I'm going to switch over to the drip line with the built in emitters as it does a much better job of watering without all the over spray and it is much more low maintenance than the micro sprays. I never know one of the sprays has clogged until I have stressed plants, where the drip line never clogs. :o) They also have 1/4 emitter tubing..I may try that instead in my smaller beds.

Everett, WA(Zone 8a)

I think you're right that it gives better results to start with a reasonable pressure, and limit the length of the runs of narrow tubing. I ordered on 20 psi regulator and one 30 psi.

When I started with 45 PSI, I blew some tubes off my 10/32" threaded fittings. Tentatively, "Quick Threads" seem to hold a little better.

Even so, it's better design to use the pressures tghe parts are designed for and rated for!

Using a long run of narrow tubing as a flow regulator or intentional pressure drop isn't really practical, or at least that's the conclusion I'm coming to. Start with a reasonable pressure and then run main lines that are big enoguh that they don't have big pressure drops. I now have a 3/4" mainline b ackbone, and I'm adding 1/2" lines so that the 1/4" "microtubing" does not need to be long.

>> They also have 1/4 emitter tubing

Yes, and I have a length of that. Mayeb the "wet spot" is wider, deeper in the soil. And maybe I just have not been running the water long enough in that bed, since I have some sprayers and one small sprinkler that I throttle back to decrease its radius.

I think the manufacturer was right to suggest limiting the length of a 1/4" dripline run to 50', or 25' for closely-spaced emitters. Run some 1/2" mainline along a bed so that no 1/4" drip-line needs to be longer than a certain length.

Fremont, NE(Zone 5b)

For sure, regulate high pressure with the regulator as opposed to attempting to do it with
your system, otherwise you will end up with problems closer to your water source and headaches trying to maintain the system when the fittings and emitters blow apart over time. Drip is designed to work under lower pressure..that is why most of the fittings are barbed instead of being threaded or requiring clamps.

Once install your regulator you are going to find you may have to do some redesigning
to your drip system. You may find that some of your areas farther from the source might be weak and in some areas if you had allot of sprays on one line they may not spray as far and possibly not even spray at all.
Most likely the 20 psi regulator will not run your current set up where as the 30 psi will with less redesigning to your current setup.

You are on the right track with using larger pipe to feed then tapping off that.
I would run 3/4" to 1" as a mainline to the bed or beds then run 1/2" through the bed and tap 1/4" off that in short runs. And depending on your beds..if it is one long run I would back feed the bed with another mainline either mid way or at the end of the run. But if you have allot of small scattered beds with mainline running to each you should not have to worry about looping.

On the drip tubing with emitters, they really need to run from 45 minutes to an hour
to water effectively. A person can still tap into this type of tubing and run individual 1/4" pipe runs to plants and pots, hanging baskets. Just make sure to use emitters that are rated for the gallons per hour you need or you will flood out your plants.
When designing a set up it is all about balance.


Everett, WA(Zone 8a)

>> When designing a set up it is all about balance.

Agreed. I started using garden-hose-Ys to add valves to my (small) system with (many small) raised beds.

But even when turning areas on and off by hand, each area has to be balanced within itself: either all slow drippers, or all fast sprayers.

I'm still learning (playing).

(Pam) Warren, CT(Zone 5b)

[quote="RickCorey_WA" But even when turning areas on and off by hand, each area has to be balanced within itself: either all slow drippers, or all fast sprayers. ]>>

Why is that? Doesn't it make sense to use sprayers for the needier areas, and slower drips for the ones that need less water? My garden is on a steep hill which is terraced, the levels defined by stone walls. On the middle level is a long border of perennials in front of a 2-3' stone wall, and on the level above there are very established daylilies and peonies, with a few hardy plants draping over the edge. Drip hose seems to be enough up there, but I have sprayers for the border. Am I doing something wrong? I just put the system in this summer, then was away for weeks, so I haven't really gotten the feel of how it's working. Nothing important died, I know that much. But whether the weather was kind or I was just lucky and hit it right the first time, I do not know.

Any input appreciated...


Fremont, NE(Zone 5b)

Your set up sounds like it is fine because your plants in the drip line area do not require as much water. The drip line needs to run longer than some sprays to achieve the same amount of in turn you might end up over or under watering one area but because the plants in your drip area require less water it works fine in your situation.

It really does not make more sense to place sprays in the more needier areas.
Actually the drip line works better. You do not end up with allot of over-spray and watering areas that you don't need to and if you put mulch over the drip line it holds the moisture in the ground and because it is not sticking up out of the ground there is nothing for the wildlife or pets to decide to lean against and lay over in the ground.. And depending on when you water you don't lose water to evaporation. Another thing to consider is that drip line with the built in emitters
are designed not to clog. Basically you install it and forget about it. Where the sprays are more finicky, they will clog overtime( they are micro sprays so you are dealing with a much smaller opening which only takes a small particle to partially close it off or totally close it off) and if your pressure fluctuates at all when you run a washer or something inside the house they may not water as far out as you think they are.

Of all the drip systems I have installed it is the ones that have sprays or remote drip emitters that we have the most service calls for. The drip line with built in emitters performs the best overtime with almost no maintenance other than when someone accidentally hits the line with a spade.

The only negative thing I have found about the drip line with the emitters is that it crimps easily. So when installing or moving it a person needs to be careful not to attempt to make too tight of bends with it or you will crimp it off.
This is really not a negative but a drip zone needs to run 45 minutes to an hour depending on the type of soil you have and the water requirements for your plants.
Most drip lines put down around 1 gallon per hour.

With all the said I still like the sprays and use them at my home but only because I have several areas where I have groups of pots and I find using the sprays are easier than running a drip line to each pot when they are in groups. But when I install a system for someone else I always run the lines to each pot. Most people that hire us to install a system are doing so because they want to set the controller and know the system is watering their lawn and flowers without worrying if it is going to work or not.

(Pam) Warren, CT(Zone 5b)

Thank you so much! I gave myself a crash course and got great support from Dripworks before installing the system, but still had to guess a lot. Hearing from a pro, the voice of experience, is very helpful!

What spacing do you like in the emitter drip lines? They had 6, 9, and 12." I went with 9" figuring I'd loop it where needed. I was surprised to find out there's a maximum length of 21' recommended per run. Mine is 1/4" coming off 1/2" main line. I'm thinking in the spring to switch to 3/4" mainline for the most densely planted areas because the borders are quite long. I do use 30 psi regulators on the 2 zones I have now, and It does seem that there is good pressure all the way to the end of the run, but I want the option to add on if needed without worrying about fall-off.

I chose sprayers because in the past I've found that drip hoses - I know, not the same thing- watered in narrow strips with dry patches in between, and spray hoses with the perforations did a better job in dense plantings. I chose the new system because the scope and configuration of this garden made that kind of setup unwieldly, unsightly and less effective in the long run. Also I used sprayers because I wanted to see where the water went when I turned the system on rather than trying to guess what was happening underground as the water from the emitters spread. As time goes on I may heed your advice and slowly switch over to more drip lines as my confidence grows, especially if the sprayers become unreliable.

Thanks again!


Everett, WA(Zone 8a)

I'm very new to this, setting up my first system and learning as I go. My soil differs from bed to bed, since I made the soil in batches and each batch is different. Also, the soil chnages its structure a lot as the relatively small amounts of added compost tends to get "eaten" each year, and each bed has a different amount of compost remianing at any given time.

My issue with dripline is that the first one I tried had 12" spacing, and I never ran it long enough to see the "wet spots" get bigger than 3-4" in diameter. My thought was that I didn't want a drip system that only irrigated 1/3 of each row, and needed to be laid down in lines only 4" apart.

From what you say, I should have been watering the dripline bed for 2-3 times as long as I did. And maybe trusting the water to dpread a lot wider undergorund than it did on the surface.

Once I tried to figure out the cost of dripline vs sprayers. At first I thought it was no contest, that dripline cost
43 or 60 cents per GPH, and needed to laid REALLY close together to water all the soil.

1/4" dripline: 6" spacing x 100 feet x 1/2GPH = 50 GPH for $21.50 = 43 cents per GPH
1/4" dripline 12" spacing x 100 feet x 1/2 GPH = 25 GPH for $15 = 60 cents per GPH

In contrast, sprayers and spinners cost only 20 cents for a spray jet head, or $1.00 for a spinner, and each covered 100 to 1,000 square feet with one sprayer. With spray jets from 7-30 GPH and spinners from 10-46 GPH, it seemed to me that these cost only 1 - 3 - 10 cents per GPH.

(That ignored the fact that a timer makes it easy to run a dripline 20 or 60 times longer than I would have run a spinner or sprayer.)

Worse, it ignored the fact that I would need 1-2 barb connectors and a few feet of 1/4" micro-tubing per sprayer. Or, if if I was lazy and gadget-crazy, I would use 2-3 barb fittings including Tees, PLUS Rigid Riser tubing, and maybe a plastic stake. Even a two-barb 1/4" connector costs 16 cents, almost as much as the sprayhead.

That doubles or triples or quadruples the overall cost of using each spray head!

sprayers: 20 cents for 7-30 GPH Say 6 foot to 9 foot diameter (113 - 254 square feet)
plus 30-90 cents for fittings and tubing
plus a stake for 20-60 cents.
plus maybe a flow valve!
Call it 50 cents to $1.70 per sprayer since you might tie a sprayer to a stick, or pay for frippery..
Say anywhere in the range of 2-25 cents per GPH for small sprayers

Antelco Small Spinners (Roto-Spray not Roro-Rain) $1.00 10-46 GPH 18-25 feet diameter
2-10 cents per GPH for small spinners, but the minum efficient area is around 18 foot diamter , 1,000 square feet.

So now I understand that the cost tradeoff depends on too many things to say that sprayer are cheapr than dripline. As long as your soil DOES spread the dripped water out enough to give you uniform irrigation, the dripline is more efficent in terms of plants per gallon (water bill).

Everett, WA(Zone 8a)

>> use sprayers for the needier areas, and slower drips for the ones that need less water?

You're quite right. I was thinking of my own situation, where the water need within any one zone is pretty uniform.

If I had one bed with some Water Convolvulus and one drought-tolerant Lion's Ear, I would put Shrubblers or sprayers all over the Water Convolvulus and (at most) a dripper or two near the Lion's Ear.

Or if I mixed Sages with Brassicas, I would drip slowly on the Sages and spray the Brassicas more heavily.

Contra Costa County, CA(Zone 9b)

Do a bit of research into the wetting patterns of different soils.
A sandy soil will get wet pretty much straight down from where the water is applied. Not a lot of sideways movement.
A soil with somewhat finer particles, more of a silt, or a soil that is high in compost will get wet in a wider pattern when you look under the surface. Sort of shaped like an egg: Small surface spot (the pointed end of the egg) then a wider space under the surface (the wider part of the egg).
A clay soil might puddle at the surface, and the water will not soak in very deep (Think again about that egg shape, but lay the egg over on its side).

So do not look at the soil surface to determine the effectiveness of the irrigation.

A good mulch on the soil surface can help in many ways.
1) Keeping the soil surface softer so the water can soak in easier.
2) Slowly decomposing to help the soil.
3) Reducing evaporation so the water stays in the soil.

You can alter the parts of the drip system to accommodate different plants. Think about each unit. How many gallons per hour will it deliver? Over what size area (dripper or sprayer)? What sort of wetting pattern does your soil have? How much water does each plant need?

Lay out the systems so that plants with similar needs can be irrigated together, and plants that need some other schedule are on a different valve.
Some ways these might vary:
Sun vs shaded parts of the garden
Species of plants grouped such as 'low water use' or 'moisture loving' or 'shallow rooted' or 'deep rooted' and other considerations. A Lavender growing in the sun still demands less frequent water than an Azalea growing in the shade.

Post a Reply to this Thread

Please or register to post.

Upload Images to your reply

    You may upload up to 5 images