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I finished making my fox (and cat) scarer using one of those noisy impulse water
sprinklers. This is controlled by a PIR which activates a 12v solenoid valve
connected to the garden hose that then connects to the sprinkler.

It works a real treat but the problem is that solenoid slams shut instantaneously.
This sends a shock wave back through the water system. And the result was that
the shock waves caused a water leak at a junction of the incoming water supply
from the street.

If, as you say, the shock is causing a leak in your domestic supply
pipework (not your hose or hose fittings) then your pipework or that of
your supplier is faulty. Solution, fix it, or have them fix theirs.

My question is to find out if there's an easy way to overcome the shock wave
problem - either by:-
1. Electrical solution to close the solenoid progressively - whilst still making it
open instantly.
or
2. Some mechanical means in a pressure vessel or whatever?

All suggestions are welcome.

If you are talking about the shock affecting the hose fittings then the
following may help:

By nature, solenoids are bangy, they operate with more and more force as
they close so it is an inherent problem. You can get slow close solenoid
operated valves for irrigation but they are a bit slow in operation so I
doubt they would be suitable.

You can get shock arrestor capsules (similar to expansion vessels) for
use on water systems. See water hammer arrester half way down this page:

http://www.bes.co.uk/products/109.asp

The inverted pipe idea wont work long term as the air will be
re-absorbed by water under pressure.
--
fred
it's a ba-na-na . . . .