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What size pipes for enough water pressure from three water barrels?

TjhandyTjhandy Posts: 4
in Tools and techniques
Hi, What size diameter pipework/hose will I need to install to get decent water flow from a water butt to my veg bed drippers please? 15mm / 25mm etc? I know I can simply use hozelock type fittings and a hosepipe, but my gut feeling is that the small diameter of the hoselock fittings and a standard waterbutt tap will limit the flow to such an extent that the drippers on the far end of the hosepipe might not receive any water.

Details of the setup:
I have three waist high roughly 200 litre blue barrels that I want to plumb together to use to water my two 3 metre by 1 metre veg beds this year (and potentially other areas of the garden too) I plan to run a length of hose up and down the beds a couple of times with some little dripper nozzles pushed into the hose every 12 inches or so. The veg beds are around 7 metres from the barrels and I plan to raise the barrels off the floor by about 2 feet. The drippers are these things below.

Posts

  • Hostafan1Hostafan1 Posts: 34,889
    I had one of those type of systems, and I found the water flowed to the end and came out the furthest "sprinker" first, then worked back. If that makes sense.
    Devon.
  • Hampshire_HogHampshire_Hog Posts: 1,089
    I worked with irrigation systems for many years and came across this problem on many occasions to get pressure you need height not great volume's of water.

    You will struggle to get any pressure at two feet the static head pressure of 1 foot of water is 0.433 psi
    for example     20 ft. of water has a static pressure of 8.66 because 20 ft. x 0.433 = 8.66 psi

    At the best I calculate you will only get 6ft static pressure from three barrels so
    2.598 psi the pressure is from top of water to exit of pipe no matter what area of water you have. as the tanks empty the pressure will also decrease, that's without any losses in the pipe work the pipe diameter makes no difference the pressure stay's the same.



    "You don't stop gardening because you get old, you get old because you stop gardening." - The Hampshire Hog
  • Pete.8Pete.8 Posts: 11,340
    As HH says above it'll be difficult to get enough pressure.
    To get the same pressure as you would from your domestic cold tap, your water butts would need to be raised to about 10 metres

    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • Hostafan1Hostafan1 Posts: 34,889
    you might be better with those soaker hoses which "seap" rather than sprinkle?
    Devon.
  • ForrestgrumpForrestgrump Posts: 247
    Agree with Hostafan I think you would get more luck with soak hose from what your saying its 21 meters +

    I would suggest 19mm 22mm or 25mm if you can get it to the joining point the larger will give least resistance but I would not go above 25mm or you will start to get back flow resistance as its a gravity system.

    I have had some success with sprinkler systems using a small hose pump you can get theses to fit a drill and using one with a battery will work. Or if you want to get really adventurous you could probable rig up a 12 Vdc one to an old car battery would give you a longer run time. (might even try that myself at the allotment)
    If you have a garden and a library, you have everything you need.
  • TjhandyTjhandy Posts: 4
    Thanks all, so from what I think you're saying there @Hampshire_Hog I might as well just use standard hosepipe diameter fittings as the lack of head will far outweigh any losses in pipework? I'm not expecting mains tap pressure, or jets from the water emitters, but want to make sure that water at least trickles out of the far end of the hosepipe water drippers as per the image above.

    Guess I'll have to try it and if it's no good, I can try adding a 12v pump with an old car battery (I have an old battery as luck would have it) as @The Gardeners Boy has suggested. I think hosepipe fittings might also be the cheapest option too. Many of the fittings are less than £1 on ebay for tees, and elbows etc. 

    @The Gardeners Boy yes, with the back and forth laying of the hose on the beds, and then the 7 metres back to the barrels it would be around 20 metres of total pipe length.

  • SkandiSkandi Posts: 1,723
    I have found that a standard hose pipe is good for around 70m of piping from the tap, over that and internal friction makes flow rate drop too much. From my water butt (1100L) which is raised around 2m above the beds 25m is the maximum it can manage on a standard hose.
  • raisingirlraisingirl Posts: 7,093
    Tjhandy said:
    Thanks all, so from what I think you're saying there @Hampshire_Hog I might as well just use standard hosepipe diameter fittings as the lack of head will far outweigh any losses in pipework? 
    The losses in the fittings far outweigh the losses in the pipe, so have as few as you can and try to only have 'full bore' fittings - i.e. the hole in the spigot/bend/tap is the same diameter as the hole in the hosepipe. Many valves/taps especially - even when they are fully open - still create some restriction. One partially shut tap will lose you more pressure than 20m of even diameter hose pipe.
    Gardening on the edge of Exmoor, in Devon

    “It's still magic even if you know how it's done.” 
  • TjhandyTjhandy Posts: 4
    Skandi said:
    I have found that a standard hose pipe is good for around 70m of piping from the tap, over that and internal friction makes flow rate drop too much. From my water butt (1100L) which is raised around 2m above the beds 25m is the maximum it can manage on a standard hose.
    Thanks @Skandi
     
  • TjhandyTjhandy Posts: 4
    @raisingirl thanks, I'm now looking at 32mm/40mm solvent weld waste pipe and fittings for the main connections... seem cheap, less than £1 per elbow/tee. Ball valves are a bit more, but still not bad, particularly if sourced from ebay chinese stores (£5 for two), then some kind of filter before stepping down into the hosepipe with some kind of reducer. My thoughts are that this size might reduce the chance of a blockage that would be difficult to clean out. 
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