My query over 30m of 20mm water pipe and a solenoid valve with regards
to water hammer has been found not to exist.

It seems that the solenoid valve I have isn't "direct drive" so it opens
and closes with a slight delay. I have however stuck up a youtube vid
showing the horrendous racket given off by the cleaning pump (which I
suspect might be a faulty unit to make such noise) and the silence and
efficiency of having replaced it with a solenoid valve.
http://www.youtube.com/watch?v=CTNuvTWrfis

The additional "T" into the pipe work is capped off with another
solenoid valve which might get used either as an auto top-up for the
pond or I might try and rig up an out-door IR sensor hooked up to a
water sprinkler (something like
http://www.easywatering.co.uk/acatalog/impulse_sprinkler.html" to keep
the cats away...



And a camera to catch the action