Low water pressure on automatic system

[Matthew Johnson]

I have installed a watering system for my plants although I haven't automated it yet. I wanted to get it running right before I spent more money on solenoids and a irrigation controller.
my system runs off a 25mm pipe that feeds a 3 way manifold.
I have 2 19mm pipes that run along the fence line and along the front of my bench.
I have around 60 trees and 30 sprayers on the lines.
I tried to run a 6mm pipe with a sprayer on the end to 2 tree's that are on a trolley but the water pressure was non existent by the time it reached the 6mm pipe. The 6mm line is at the end of a 19mm line, would changing the 6mm to the start of the line fix this issue or have I just reached the limit of water pressure

Any advice on how I can improve the efficiency of my system?

The only way I can think of improving the pressure is when I automate it I run the 2 lines alternately, as in the fence line first, then the bench line.

Cheers
Matt

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25mm feeder pipe

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Manifold and the 2 lines

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my collection

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line running along the top of the fence

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line running along the face of the bench

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end of the line, 6mm line runs off the right hand side of this area

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6mm line

[MoGanic]

Hi there,

I had the same issue with a system my father in law and I put in.

We had 11 pop up sprinklers all linked with one pipe.

We tried using a thicker pipe to allow more water to flow through, but that didn't make much difference.

Eventually we had to split it in half and have two separate systems for the right and left sides - and operate one at a time.

In hindsight, I would probably just use thicker pipe to increase flow rate (the thinner the pipe, the more friction, the less pressure - as opposed to common theories about decreasing pipe size to increase pressure).

So in your case, I would probably eliminate all those thinner sprinkler pipes and replace with something that connects directly in line with the thicker pipe. This would mean that you get maximum flow rate up to the point where it exits the pipes. The issue with your current set up is that it slows the water down before it reaches the exit point.

As to how much more flow this will give you - I cannot say. But it will definitely be an improvement on what's happening now.

The other option is to shorten the length of the thinner pipe - this would probably be the cheapest as you just take off the sprinkler head you have on at the moment, cut it shorter, shout "NEXT", move on to the next sprinkler, but it might not be AS effective. In theory it should still help because you're reducing flow loss due to friction over the length of the pipe.

There's probs some other options that I am unaware of, but hopefully peeps will chime in a let us both know.

Cheers,
Mo

[kcpoole]

Ah the old too many holes in a pipe problem.

Water pressure is purely a function of the amount of "head" in the system ( less any pressure reducers) and is created by elevating the water supply relative to the surrounding area (ie they pump water up to a tank on a hill or tower and let it gravity feed from there).
You cannot do anything to increase water pressure, except move house to one further down the hill.

The Amount of water you can receive through any tap, is a function of the water pressure and the size of the pipe it has to go through. Most houses in Sydney are fed via a 1/2 inch ( 13mm) copper pipe from the mains in the street. Again the only way to increase the amount of water you can get out of any tap, is to increase the size coming from the mains. ( Water authorities will not let you do that) so you are stuck with what you have.

Typically a mains pressure system will let you draw water from 2 or sometimes 3 taps simultaneously without significant pressure drop, and that is why there can be 100s of houses on a single main as most people do not have the tap on at the tame time, but around morning and afternoon peak you can notice a dropoff in pressure.

The way sprinkler systems work, is you have lots of holes that all add up together and when they get to the same area as the supply pipe, you will have very little pressure to force water through them all. They will just dribble equally.

It make no difference if you put a 25mm pipe on your side of the 13mm supply line as the pressure delivered by the system will not be increased. You will just increase the volume of water in the system

If you have 10 sprinklers on a single run and get good spray, then add another 5 and they turn to a much reduced spray then you have achieved your maximum density of sprayers. ( For me I get about 20 sprayers per run).

If you suffer poor water delivery, reduce the amount of sprayers on a single run, and run 13mm poly pipe closer to your sprayers. I find any more than 2 or 3 sprayers on a 6mm pipe to be too many.

Moganic touched on the friction losses in the pipe, and they will reduce the amount of water that the system can deliver. Reducing the pipe diameter will increase the hydrodynamic friction and thus reduce the amount of water able to pass thru it. Increasing the pipe size will go the other way, but only up to the size of the inlet pipe to the system. Above that you will reduce the available water pressure on your side which will have more detrimental affect than the lessened friction.

Ken

[Jow]

The other way to increase pressure would be with a header tank and pressure pump. (Think how a bore is setup) Fill the tank then pump into your system with pump. You would be limited by the size of tank but it would give you the pressure you might be chasing.

[Bougy Fan]

I had to split my system into 2 separate lines as it was too many sprays to give a proper coverage. I only use it when I go away, so I use 2 tap timers that work at different times to make sure there is full pressure. I just used 13mm with most spray heads running off a 4mm line. I am gradually changing over to brass spray heads as I get more water out of them.

[SteveW]

Agree totally with Ken's hydraulics lesson. Bigger pipes work best. The shorter the length of tiny tubing the better.

To add to Ken's reply, you need to do some maths.
1. Using a 10 litre bucket and stop watch (on your phone somewhere) calculate how many litres per minute your irrigation pipe is running at (eg 35 litres per minute).
2. Then read the label on your sprays to discover how many litres per minute each spray delivers (eg 5 litres per minute).
3. Divide the first figure by the second figure and you know the maximum number of sprays per line. Using my example, the limit is 7.

Check out the Toro CFX down sprays for the best sprays for bonsai. Forget drippers.

[shibui]

I think you have reached the limit of your water supply with 2 19mm lines and 30 sprays. Running the 2 separately will reduce problems.
I can only run about 12 of these sprays at one time from my system so I have to split my area into 6 separate runs to get good spray coverage.
You have 30 micro sprays on the line. Assuming they are 1/2 circle plastic ones they use 80 l per hour each = 2400 l/hr = 40 l/min. That's a fair bit of water! You can check what your tap will deliver by placing a bucket under the tap. Turn on tap and time how much water you get in 1 min (or 30 sec or 15 sec if bucket overflows in less than 1 min) Many garden taps will only supply around 20 l/min so clearly cannot run 20 of these sprays.
When you have calculated tap capacity allow half that for pipe losses (may be more or less depending on pipe diam and length) That's how many sprays you can run at any 1 time.
As has already been said, smaller pipe reduces flow and pressure substantially.
Head loss tables show that 40 l/min through 19 mm poly will reduce pressure by 30m head/ 1000m of pipe = 30kpa/ 100m = 3kpa/ 10m. The water is off in the pic with pressure gauge but mains pressure is around 200 so a loss of 15 or 20 kpa before you even use any water is quite significant. It is a good thing you have used 25mm pipe to get water from the tap to the 2 lines or there would be even less pressure to play with (pressure loss in 25 mm poly is 1/3 of what 19mm loses)

The 6mm pipe at the end of your system starts with reduced pressure after traveling through the 19mm pipe and is further reduced by all the sprays taking some more pressure and flow then further restricts through the smaller pipe. No wonder there's not much left.
All this is pretty technical so in easy to understand terms:
Moving the 6 mm spaghetti to the start of the 19 mm pipe will help a little.
Shortening the 6 mm spaghetti will help more but I think reducing overall flow by separating the system into 2 sections so there is less demand at any time would give the best result.

[Matthew Johnson]

Thanks for the feedback everyone, what a knowledge base this place has!

When I first set up the line I wanted to check for leaks, I turned the system on before I attached any sprayers.
The pressure gauge on the manifold was about 240 kpa, I had the system running today and it showed 40kpa after the system was fully running.
The reason for this thread was due to the thought of what I would do if I needed to expand the system. running sections is definitely the answer!


Cheers
Matt

[JaseH]

Check out the Toro CFX down sprays for the best sprays for bonsai. Forget drippers.

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