I've checked the pictures against the schematic, the diodes do match the orientation of the way the direction that voltage flows, a check with the multi meter confirms voltage is flowing from the source, which in this case are the outputs from the PIKO switch decoder.
The PIKO switch decoder, maybe with hindsight is perhaps not the best choice, only thing to hand to work with.
Have sat quietly and studied very carefully the schematic, direction of flow from the orientation of the diodes, and have worked through the various scenarios, and had a rethink about it, and made the necessary adjustments or corrections.
OK, after many deliberations and testing, should have payed more attention to my own gut reaction, the 104 Capacitor is required, the electrical noise generated by the relay when switching is horrendous.
Breadboard circuit used for testing, has been thoroughly checked, rechecked, tested and retested, with a LED, Relay, conventional Digital Multi Meter and a Scope Meter....
Debatable as to whether the Relay itself useful for switching a Solenoid Air valve, not only because of having to use both a Positive and Negative voltage to activate the Relay, no protection, can be afforded to the 5475 outputs to protect them from the resulting voltage spike that occurs when the coil of the Relay collapses either due to using the button to activate the Relay on or off, or an interruption to the power which causes the coil to collapse, and whether the Relay contacts are man enough to keep switching a Solenoid on and off
It a nutshell, and it's highly unlikely that the 5475 outputs have any form or at best a very mediocre protection, after all it was original designed for voltage to flow out from the 5475 outputs.
I'll wager the designers never expected that anyone would come up with an idea for a circuit for voltage to flow back into it.
From testing using a steady fixed voltage supply of 12V, and from the coil collapsing, voltage will shoot straight back into the inputs, probably destroying the whole unit in the blink of an eye.
Bottom Line..after all this, the Simple Circuit as suggested using a Relay...will require additional circuitry, Transistor, Resistor, Capacitor, and a Zenner Diode to provide the necessary protection to prevent "flyback" from the Relay Coil from damaging the 5475.
Plan B it is then............
Although, as with everything in life, from the circuit and subsequent schematics did discover a few useful tricks and ideas for the non conventional use of PIKO Switch Decoder outputs....
And, naturally I did learn something else, should have paid more attention and heeded the advice from my correspondents on the American Garden Railway Forums, now been put in place.......................
The rest, well......... The problem for me is I do not understand electrical schematics, let alone any terminology surrounding them. By "plug & play" I meant just that. It either does what it says on the tin or it doesn't. How it does it I probably don't have a clue, but I'll try. To quote Arthur C Clarke - "Any sufficiently advanced technology is indistinguishable from magic". I'm at the stage where whatever the solution is it will probably fit that quote to my eyes and feeble mind 
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