Hi I'm new to the forum and am very interested in what you guys are saying with regards to CO2 regulators and solenoid valves as I am in the throws of setting up a planted aquaria, or shoudl I say it's still in the planing stages at the moment! "Research thoroughly and then get your hands wet" is what I say!
With regards to the removal of the plug invalidating the warranty! I would be very surprised that any supplier would dis-honor their agreament if the product was to be at fault, after all there would only be two wires (Live and Neutral) on all 100 to 230Vac switching solenoids. Please note all european cables are harmonized now days so Live is Brown and Neutral is Blue and fit your BS1363 (13amp plug) with a 3 amp fuse.
Regards American cable standards, these are different, typically Black, White, and Green. Black is Live - White is Neutral, and the Green is Earth.
Make sure you know what switching voltage your solenoid is, there are also DC options, which in theory would be far safer to use in the vacinity of water, but obviously you would need to suorce an additional power source to step your AC supply to the DC supply required.
BUT REMEMBER - IF IN DOUBT CONSULT AN EXPERT!!!!!