On Sun, 08 May 2016 12:47:43 +0100, T i m wrote:

On Sun, 08 May 2016 10:13:41 +0100, MM wrote:

[snipped for brevity where appropriate]
Having read up on the whole issue of gravity irrigation in the past
couple of days, it's becoming pretty apparent that the problem is lack
of water pressure. One might assume that 230 litres of water would
provide plenty of pressure, but it's actually minimal.

Quite (been there found that out etc) so what you want is a controlled
'flow' (fairly independent of back pressure) over sufficient time as
to ensure all the plants had sufficient water each day, just as if you
walked along with a watering can? All you would need to do to test
that is to pull off all 6 drippers, turn on the timer and see how long
it took for the worst case to have been given sufficient water. If it
takes 5 mins then you could set it to P2 (2 / 2m / day)?

Agreed. My basic problem is that I *assumed* it would all just work! I
should have started planning the system weeks ago. Too late now,
because my British Airways plane is already on the tarmac, so to
speak. But all your tips will be looked into when I get back.

I know when I kept tropical fish is was difficult to balance any
air-bricks or air powered filters if the air hose was in a single line
(Tee'd from the same bore hose). So I made up a plenum chamber from a
tin can with some brass tubes soldered in and that made things much
easier. It was interesting to see this can 'inflate' slightly as the
pump brought the system up to pressure (I had one of those induction
motor piston pumps and the plenum also ironed out the pump 'strokes').

Yep. These are all things I'm going to look into after the hols!

You may not need to if my suggestion above works? I think the thing
here is as you say / read up on is that you are running what could be
high pressure drippers off a low pressure system. So, you either
provide that pressure (automatic pump (only comes on when the outlet
is drawing water via the timer) in the butt with a low level cutoff)
or change to a system that uses flow.

I, too, thought of an inline pump (e.g. Whale Standard 12V Submersible
Electric Pump) somehow wired into the Hozelock so that when the
Hozelock opens the valve the pump comes on. That would surely provide
enough pressure to feed twenty pots.

Assuming all your drippers are supposed to be the same, it would be
interesting to see how they compared when they were all fed in
parallel, rather than series?

Ditto.

Even when running mains pressure feeds to my runner bean plants (also
via a Hoselock timer) it was interesting to see the wide range of
'jets' you saw across all the outlets, even when being fed from a
common larger bore hose.

Yeah, but you got jets!

You could only hear them as they were under that black weed-control
fabric. ;-)

Prior to the drip feed gubbins I used my own
watering pipe design, consisting of about a 2 metre length of 15mm
copper tubing (as used for plumbing) and a hose connector on the end.
I squashed the other end of the copper pipe flat so that it didn't
leak. Then I drilled small holes along the pipe. Connected to the
mains I, too, got amazing jets! All different directions. It
functioned as a rudimentary lawn sprinkler and I've had it for at
least 15 years.

So that was the plenum type design, cool. ;-)

It worked/works very well when I was living very frugally while
waiting for the pensions to kick in and couldn't justify a sprinkler,
which I now have treated myself to a couple of years ago (from Wilko).

So then the tomatoes and holiday. What to do? So that year (last year)
I had planted out the tomatoes in large plastic storage bins, three
plants per bin, effectively giant "grow bags". It was easy to pull
them together in a line so that I could lay my copper watering pipe
across them all. Bingo! A lot of water sprayed on to the lawn, sure,
but a heck of a lot got to the plants. The perfect solution. A
Hozelock water timer was bought and I sat in the garden, in testing
mode, waiting agog for the timer to switch on for its 2 minutes every
6 hours. It did and I was so pleased I went and made a cup of tea.

Hehe.

Then I had nightmares the whole holiday when I was away as to what
could happen if the Hozlock timer "froze" with the valve OPEN due to a
battery or internal circuit problem*. I was imagining water bills in
excess of £1,000. So I said, never again.

Yup, can be a risk if on a metered supply.

Ah, yes! Good point. Where I used to live in Bucks we had no meters!
It wouldn't have mattered (well, my conscience would have pricked a
bit).

Hence the water butt and
this latest experiment. If it's a total failure and I return to find
the tomato plants all dead, it's not too late to sow fresh seeds.

I was going to say 'yes, no lives have been lost' but I guess that
depends on how 'green' you are. ;-)

Well, actually, three won't be dead, because my brother had better
water them (see above)!

;-)

* Hozelock caution against using rechargeable batteries. Apparently,
the discharge rate of rechargeables is unpredictable, compared to
non-rechargeables, which ARE predictable. So, what the timer does,
before opening the valve when a watering event is due, is test the
batteries for enough power to close it again, and if there isn't
enough, it won't open it.

That's clever. Funnily I just took a Hoselock timer to bits (I believe
it was split in the frost but it might not have been) and it was
interesting to see how it worked (mechanically).

How weird! No, not that you took it to bits, but that *I* had EXACTLY
the same thought myself over the past day or two, especially when I
started considering that inline pump and what would be involved in
hooking up a Raspberry pi or Basic Stamp to the circuitry. However, I
haven't dismantled mine yet, as it wasn't cheap. What is actually
inside these timers?

When rechargeable batteries are used,
however, the timer may "think" there's enough juice left, but there
isn't. So the valve opens... and then will not close. Result:
Permanently open until one returns to find water, water everywhere!

;-(

One might be lucky if the neighbours noticed excess water and switched
the water off at the meter in the pavement, but they might be on
holiday, too.

Or wonder why their hose was flooded? ;-)

Of course, I've NEVER used rechargeables for the water timer!

I think that because there is such a difference in voltage between an
alkaline and typical rechargeable equiv (NiCad or NiMh etc), the good
systems allow you to select which is installed and the 'Low battery'
warning (or process, as in the Hoselock AC1) would be able to work
more accurately. My Garmin GPS III+ and V were such devices and you
would tell it which type of cell was fitted and it would warn / shut
down at different voltages.

I love technology!

I am interested in your experiments as Mum has a couple of large water
butts and a load of pot plants she would like watered when away for a
few days (rather than just relying on us).

Okay, well, wtatch this space, because as soon as I've worked out a
viable *long-term* solution, I'll document it. Probably re-inventing
the wheel, but there ya go. It's all rather too daft for some people,
who say you can buy tomatoes at Tesco or Asda any day of the week, why
Bother? But you have to try these things! (I tell 'em.)

She has a pump in one so we can use a hose when there but something
automatic and reliable would be better. I had considered using the
pump to automatically feed a header tank mounted up higher and
something like an Arduino and float switches to manage the levels but
I think there are low voltage pumped - solar systems out there already
that do similar.

Cheers, T i m

Ditto

MM