On 10/02/2021 13:12, Chris J Dixon wrote:
I have, with some success, been using a porous hose to water some
of my flower beds, as they are rather dry because of clay soil, a
neighbour's ivy hedge and trees in both gardens.

The side border is about 1 m x 8 m, leading to an area of about
20 sq m across the bottom of the garden.

I currently feed from the house, via a pressure reducer and
timer, to both ends of what is essentially a loop, down the side
border, leading to meanders to cover the most distant area.
Naturally, the pressure, and hence flow, drops off at the end of
the run.

As some of the hose is now a little _too_ leaky and fragile if
jointed, I am looking to replace it this spring, before
everything bursts into growth.

Something tells me that there ought to be a simple way to work
out how to get best coverage (some sort of resistor
calculation?). I guess a separate feed hose with reduced flow
resistance, supplying sub-sections, might be the way, but I fear
the maths might point to many short stubs, which means more
joints and leak opportunities.

Chris

One complication in trying to calculate it formally is that the flow
rate, and hence velocity decreases the further you get down the line
because of the deliberate leakage. And that will affect the pipe
friction (or pressure loss). You could investigate this with a simple
pressure gauge. With it running, if the pressure at the far end is
similar to that at the start, then it is not much of an issue (and vice
versa). Another factor is that the permeability of different sections of
pipe may vary from manufacturing variations.

If you identify "dry spots" either because of this factor or because you
are at the end of the run, you could increase the porosity of these bits
by applying pointy objects. You might need a bit of trial and error to
find the right hole size. (I once manufactured a "sprinkler" system
based on a flat spiral of hosepipe, with regular drillings of around
1/16 inch made using a cordless drill).