On Tue, 23 Oct 2012 11:54:00 +0100
Harry Bloomfield wrote:

presented the following explanation :
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.

I tested that idea around 20 years ago :-)

I gave the idea up simply because our water pressure was not
sufficient to provide a jet of water quickly enough on the opening of
the solenoid.

One solution to the shock, might be to T in a length of hose pipe
between solenoid and water supply. If the new length of pipe were
maintained full of air, then because the air is and the hose are
compressible, it would act as a buffer to the shock.


That is a perfectly sound idea, used in industry as well as some
domestic situations. I have seen it in a basement at the utility sink. I
once had the same problem with a four-inch water supply pipe, which
descended vertically from a plant ceiling for more than 40 feet before
meeting a solenoid valve. The resulting shock made the pipe's
horizontal run, before the change to the vertical, move a foot sideways
at its worst. We tried these shock absorbers, but they weren't man
enough for this job.
It was fixed by installing a slow stepping valve, at the top of
the vertical drop, which was slow enough to gradually control the
water flowrate.
Getting up to the valve was an experience in itself.
--
Davey.