Questions re soaker hoses,

Hoping there might be some irrigation experts hanging out in here who can help me with a couple of questions I can't find answers to re soaker hoses.

Firstly, background info: I've just installed a bunch of soaker hoses in my front garden – 5 in total, setup in parallel. There is a 2-way splitter on the faucet, one side of which connects directly to one soaker hose (15m long, with about 2m of garden hose in the middle to bridge a non-garden area), and the other side of which connects to about 15m of garden hose. Said garden hose then connects to a 4-way splitter, onto which connect four short (1-2m) lengths of additional garden hose which then in turn connect to four soaker hoses in lengths of ~7m, ~10m, 30m and ~25m. The soaker hoses are all the recycled rubber variety that slowly "sweat" water. Pope branded, from memory.

That aside, the questions:

1) This may be a dumb question, but I cannot for the life of me figure out the answer (either thinking it through or Googling) – or should I say, I think I know the answer but would like confirmation.

I know that I'm meant to use a 10psi pressure regulator to help the hoses release water evenly along their length, and to stop damage / blow-outs. Bunnings sell a 100kpa regulator, which I figure is close enough.

What I can't figure out is if I just need one pressure regulator for all five hoses (connected directly to the faucet, before the water splits into five separate paths), or five pressure regulators (one immediately before the start of each individual soaker hose – after the water splits into each separate path).

I think the answer is just one, as pressure and flow rate are different things, and hence the single regulator will keep the pressure around 100kpa no matter how many / how long soaker hoses I connect after it (until I reach the flow limit of the mains water / faucet anyway).

But, as I said earlier, I'm not 100% sure on this. Can anyone confirm?

2) On a similar note, I keep reading that you should only turn the tap on ¼ – ½ a turn when using soaker hoses. Does this rule still apply when you have pressure regulator(s) in place? I'm thinking it doesn't – that the ¼ – ½ turn rule is a primitive method of regulating pressure via reduced flow – and hence you can just turn the tap on full bore, but again, I'm 100% not sure. Anyone?

3) Do you actually need a backflow preventer with soaker hoses? I keep reading online that you should have one (for your health, and/or by law), but for some reason I'm struggling to find a shop which sells them.

Thanks in advance for any responses / advice – appreciate it!

So...you have...

Garden hose...approximately 24 metres.
Soaker hose...approximately 87 metres.

First issue...you should never use garden hose if it is continually exposed to UV. You should have used UV stabilised 19 mm or 25 mm (LDPE) poly pipe.

When you say "garden hose", are you referring to the common 12 mm variety?

You have also not stated the soaker hose's internal diameter but I am guessing 13 mm.

You also don't say what the soaker hose's drip rate per metre/hour is. A normal low pressure drip hose's emitter will drip at about 2 litres per hour and at about 4 litres per minute over a 30 metre length. If we assume that the soaker hose (product unknown) is about the same drip rate per metre, then this 'rough' calculation gives a total design drip rate of approximately 11.6 litres per minute or a velocity of approximately 1.7 metres per second through 12 mm hose.

You then need to determine the tap's flow rate per minute through the pressure reducer. The required flow rate of 11.6 litres per minute would be subject to friction losses of approximately 2 kPa per metre.

The 100 kPa reducer could not overcome the friction losses in the garden and soaker hoses to supply the required pressure distribution and flow rate needed for an even drip rate over the full length of hose.

Thanks for the response SaveH20. Unfortunately parts of it have confused me - but I'm trying to get it!



Yep, I mean common variety garden hose - the sort of hose you find in every garden. I don't know precisely the diameter, but 12mm sounds about right. Luckily the garden hose is not a permanent part of the system - it's uncoiled and connected to the 4-way splitter when I'm watering, then put away again - so no UV issues.



It's 12mm - sorry for not mentioning that previously.



I unfortunately don't know what the drop rate per meter per hour is - it didn't say on the product packaging, and Pope's website doesn't shed any light on it. The product in question is this one: http://www.popeproducts.com.au/products ... -12mm-coil.

Your approximation of my hose to a low pressure drip hose is probably a good start, but I would've thought these soaker hoses emit more water than a drip hose? I say this purely because I keep reading that drip hoses are more water efficient than a soaker hose? Or is that a reference to specific placing of the drip emitters next to plants, rather than to total water egress rate?



This is where I start to get confused. I understand what you're saying re total drip rate design, need to measure the flow rate post-pressure-reducer, and ensure there is sufficient flow. Where I'm lost is:

- do I need the post-pressure-reducer flow rate to be exactly the same (or as close to exactly the same as possible) as the design drip rate? Or is higher OK - just lower is not?

- when you talk about friction losses of 2kPa/metre, do you mean that 2kPa is lost per metre of soaker hose? Hence if the pressure at the start of a hose was 100kPa, after 10 metres the pressure will have dropped to 80kPa? Assuming this is correct, what would happen to the pressure if there were two soaker hoses connected in parallel - would the pressure after 10m in each hose be 80kPa or 60kPa? I ask this because it will answer one of my original questions about pressure in hoses-run-in-parallel.

If you don't mind answering the two above questions that would be fantastic, as it will greatly help with my understanding of all this.

Thanks!

Hi Matt,

I did look at the Pope site but I couldn't find the weeper hose, thanks for linking it. It is annoying when companies do not show product information that is important to know when designing a system using their product. Does the packaging state that a 10 psi reducer is recommended?



Your 100 kPa reducer is roughly 6.75 psi. The 10 psi recommendation is to prevent damage to the hose; using higher than recommended pressures can expand some weep passages and the hose will end up with an uneven distribution along its length and people sometimes end up with weep hoses that more look like sprays. Using your 100 kPa pressure reducer is no problem, it just means that the water will come out a bit slower, thats all.

Re the reference to design rate; a regular drip hose is generally designed with emitters that flow at 2 litres per hour as this is considered to be the most efficient hydraulic conductivity rate of seepage. Some hoses however will drip at a rate higher than this. The emitters are generally 300 mm apart, again for hydraulic conductivity purposes. Soaker hoses however weep along their entire length and are more efficient.

I have had to make some generalised assumptions with your system but if you work on the figure of 11.6 litres per minute, this is guesstimated on the optimal flow rate for best efficiency PROVIDED all hoses receive even pressures. If you have less than the optimal figure, then it is no real problem as the drip rate will be a bit slower BUT this will result in an uneven distribution.



The greater the flow rate, the greater the pressure loss per metre. There are a few basic things that need to be understood.

You have 100 kPa head pressure.

To double the flow rate, you need four times the head pressure.

The higher the flow rate, the greater the friction loss. If the reducer cannot deliver 11.6 lpm, then the head loss per metre will be lower as there will be a lower flow rate.

Doubling a pipe's diameter increases the volume X 4. (pi x r x r).

Doubling the pipe's diameter and maintaining the same head will increase the flow rate x 6.

The best way to lay out a drip system is to use LDPE poly pipe as the main line and branch the feed lines off it. The larger poly pipe has less friction loss and will supply a greater evenness of pressure to all soaker hoses. The feed (drip/soak) hose should not be a dead end offshoot; it is best to branch off the poly pipe and return the hose back into the branch line, completing the loop.

With your set up, you have (from the reducer) a straight 15 metre length of 12 mm soaker hose connected to 17 metres of 12 mm garden hose that connects to a 4 way splitter that supplies another 4 soaker hoses. This means that the initial 15 metre soaker hose is the beneficiary of the 100 kPa pressure PLUS it is also aided by the 17 metres of 12 mm garden hose generating a considerable restriction between the soaker hose and the splitter. Meanwhile, the four 12 mm soaker hoses (total length of 72 metres) are supplied by a 4 way splitter that receives water from a 100 kPa reducer that has to push water through 32 metres of 12 mm hose before it supplies the splitter, resulting in considerable friction and flow losses.

Hi SaveH20,


Thanks for the further reply - and sorry mine has been slow.



Not specifically, but 10psi seems to be the general recommendation for soaker hoses. Also, the 100kpa pressure reducer Pope themselves sell says "ideal for use with xxx, yyy and Water Weeper [brand of hose I bought] which operate at a very low pressure".



Isn't 100kPa roughly 14-15psi? That's what a couple of kPa -> psi calculators on the net tell me.



This, combined with my own observations, has confused me a little. I bought one of the 100 kPa pressure reducers over the weekend and tested the flow rate out of the faucet (directly into a bucket) both with and without the pressure reducer in place - both gave the same flow-rate result!

The pressure reducer has a spring loaded valve in it - would I be right in thinking the prior observation is because without anything connected behind it (water flowing straight into a bucket) it's essentially reading zero pressure "behind" it and hence not adjusting anything?

And hence it doesn't just flat-out reduce the pressure to 100kPa, but rather it dynamically adjusts flow-rate to ensure 100kPa is maintained in whatever hose(s) are connected behind it, compensating for whatever the water egress rate is from those hose? i.e. if I double the length of soaker hose "behind" it, it will increase flow-rate by 4x to maintain the same pressure (a there is now double the water egree from hoses "behind it"). And therefore I can keep connecting soaker hoses "behind" it and it will dynamically increase the flow rate through the reducer to maintain 100kPa in those hoses, up to the flow-rate limit of the facuet?

Hopefully that makes sense

A big OOPS here! 10 kPa is roughly 1.5 psi. What I did was divide 10 by 1.5 and overlooked the obvious mistake. I should have multiplied 10 x 1.5. I know better, I work with pressures - must be Alzheimers!

Most irrigation pressure reducers have a spring loaded diaphragm that resists the inflow pressure; the greater the pressure - the greater the resistance. It must also be remembered that flow velocity and pressure are separate.

Irrigation pressure regulators should state a flow rating in addition to their pressure rating so that you can buy the regulator to suit the design of your system for optimum results. They should also have a maximum inflow pressure rating. Given that your regulator will have an internal restriction that should limit the maximum pressure, I can only assume that your inflow pressure either exceeds the regulator's maximum inflow rating or the faucet's dynamic pressure is already much lower than the mains static pressure due to pipework restrictions.

We never use standard drip or soaker hoses and pressure regulators as we always use water tanks and gravity fed drip hoses or the Leeaky Hose. These operate with very low pressures and because friction loss is negligible at low flow rates, the distribution is very even but it still has to be set up correctly by using larger poly pipe main branch lines as mentioned in an earlier post and not overloading the system. 19 mm poly pipe is very cheap, about 35 cents per metre and the fittings are also cheap.

To visually understand how your system works, you need to turn your tap on and only run water through the first 15 metres of soaker hose connected to the reducer and then connect the 2 metre 12 mm garden hose and the next 15 metres of garden hose to compare the flow rate out of the end of both lengths of hose. It goes without saying that the flow rate through 32 metres of 12 mm hose (which includes 15 metres of soaker hose) will be substantially less than through 15 metres of soaker hose.

The regulator cannot sense the pressure at the end of the hose in order to...

If this was possible, the up stream hoses would be subjected to unacceptable very high pressures.

Your total length of 12 mm soaker hose is 87 metres and the total length of garden hose is 24 metres. Even without knowing the optimum drip rate per metre through the soaker hoses or the reducer's flow rate range at 100 kPa(to suit the irrigation system's design), I know that you have problems with the system as currently set up as the upstream hoses will have higher discharge rates as they are privy to higher pressure than the downstream hoses.

Hi Matt,

I need you to confirm that we are on the same page.

When I read the above, I drew a diagram of a 15 metre soaker hose connected to a 2 metre garden hose to "bridge a non garden area" in the middle and then connected on the other side to another 15 metre garden hose that then connected to a 4 way splitter that fed another 4 soaker hoses of varying lengths, making a total of 5 soaker hoses in all.

Is this correct as this is what I have based my advice on?

Or do you have hoses coming off both sides of the 2 way splitter at the tap?

The first fitment being two 7.5 metre soaker hoses with a 2 metre garden hose fitted in between the two lengths.

The second fitment being a 15 metre garden hose that connects to a 4 way splitter that feeds 4 soaker hoses of unequal lengths.

Are there actually 6 soaker hoses and not 5?

Is the 15 metre garden hose on the other side of the non garden area or on the other side of the tap/2 way splitter.

Where is the reducer fitted if it is even fitted at all?

Unfortunately, it is a hassle to upload diagrams on this forum but if you are able to, it would be appreciated.

Sorry once again for the slow reply - that time of year, and all that.



Sounds like we have crossed wires - sorry. All of the above is correct - the 7.5 + 2 + 7.5 goes one direction off a two-way splitter on the faucet, and the 15m garden hose goes the other way (to connect to the four-way splitter). Also, yes, I guess it is technically 6 soaker hoses - in my head I've been counting the 7.5m + 2m + 7.5m as one soaker hose given the 2m of garden hose is just a small bridge, but technically
it's two pieces of soaker hose.

So, to be clear, the arrangement is:



I can post a drawing of the whole system if you'd like, but I thought the above might be enough to clarify?



Not at all yet - I've just been playing around with it / testing it.

Merry Christmas!