On 6 May, 08:37, Chris J Dixon wrote:

I have a Hozelock system, which includes this timer http://www.amazon.co.uk/Hozelock-Aqu...puter/dp/B000T...

It has worked well for a couple of seasons so far. *As far as I
can tell, the timer is simply a motor driven valve. *As it opens
or closes a motor whirrs briefly. *When in operation there seems
to be no significant flow obstruction.

OK, many thanks Chris, that's useful information, I'll give it a go.