Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I also like the Wilesco D16 as the very best mid-sized engine in their stable. You have done an exceptional job of accoutrementing (apparently not a word, but you know what I mean) that steam plant for serious operation there Philip!

The fitting for using a spray bottle to top up a boiler under pressure is referred to as a Goodall Valve in live steam locomotive circles, and is a very basic device that is set up much simpler than what is referred to as a clack valve.

The Train Department is a good source of Goodall Valves on this side of the pond, but getting one to match the Wilesco or other threads may be the tricky part.

https://www.thetraindepartment.com/live-steam-parts-accessories/goodall-valves/