On 2008-05-05 13:47:54 +0100, Martin Pentreath
said:

Dear all,

I have put an automatic watering system in my garden from B&Q. After
dithering over Hozelock and Gardena systems I found B&Q did their own
which was cheaper, and seems to work very well. I've got drippers in
pots and boxes and sprayers and sprinklers for the beds. So far so
good.

Obviously the pièce de résistance for the lazy/absentee gardener is
the electronic timer to give complete automation. The problem I am
having is that the pressure of my water supply has always been a bit
marginal. Without the timer attached to the tap the system works fine.
With the timer screwed on the pressure suffers, and in particular the
sprayers and sprinklers turn feeble and don't cover the area they
should. The timer is B&Q's own £25 cheapie:
http://shortlinks.co.uk/kfv
When the water is running the timer makes a high pitched whining
noise, I guess the water is made to drive some sort of wheel for some
reason which must take some of the oomph out of it. (Incidentally I
don't use the separate pressure reducing fitting supplied with the
system for obvious reasons.)

So the question is, is it worth splashing out for a different make of
timer, or will I find the same thing happening?

Water timers actuate by means of either a gear driven ball valve (as in
Hozelock's case and some Gardena products) or a battery powered
solenoid valve (as used in other water computers, including some
Gardena and all Claber).

There are advantages and disadvantages of each. A ball valve uses less
battery power, can cope with non-drinking water but relies on water
pressure (min 0.5 - 1 bar), to some degree, to ensure complete water
shut off.

A solenoid valve uses a strong spring to create a seal (so works from
0.1 bar) and an electro magnet to open and allow water flow. This
method uses more battery power than a ball valve and can only be used
with very clean water as dirt can get trapped under the seal,
preventing the water computer from shutting off. This makes a
solenoid-actuated water computer unsuitable for use with a water
buttfor exqmple because of the likelihood of contaminants within the
water.

In short, unless you suffer from below-average mains water pressure
(the water companies are required to deliver at least 1 bar to your
boundary but may reduce that during a drought), the Hozelock
gear-driven ball valve type is the better all-rounder. FWIW, I have
been using two almost continuously for three years (hosepipe bans
excepted) without any problem.