Stuart D10 Drain Valves

Hi All,

I am just completing my machining on the cylinders of a Stuart D10 and had a couple of questions about the drain valves....

The drain vales are separate items and do not come with the kit. Can someone confirm the thread type on there?

Also the drawings do not show anything to do with the drain valves in terms of position, which side etc. Now I can guess the location as there is a 'boss' on the castings both top and bottom, left and right hand sides....however I wanted to check to see if there is any advice on the positioning. For example - I assume the drain valves should all be on the same side from a cosmetic point of view? What about which side of the cylinder? exhaust side or steam inlet side? Should the drain valve be positioned in the middle of the casted boss on the side or is there a risk that it clashes with anything like the end caps or piston movement for that matter? Maybe they need to be as low as possible such to drain the maximum amount of trapped fluid??? What exactly does the top drain valve drain....its at the top of the cylinder?

What are the drain valves actually for?! Maybe a stupid question - I am guessing the obvious is condensed water in the cylinder once steam has been shut off and the engine has cooled?

Thanks

Matt

When starting up steam will condense in the cylinder until cyl and piston are up to temp. The condensate needs to be blown out through the drains or the cylinder could "go hydraulic" ie be partly dull of liquid water and pop the covers off or split them, or worse, damage the cylinder.

Probably would not be so violent on a D10 with a small flywheel, may just stall it, but drain valves will reduce likelihood of any damage and look good too. Buy your valves and measure the threads on your items - they vary from maker to maker especially in North America. JD

The Stuart 10 series will run OK without drain cocks as the slide valve will lift and relieve the pressure until the cylinders are warmed through. They are a nice touch through and essential on much larger engines.

Neil

You would need the smallest size that Stuarts do and these are threaded 5/32 x 40 ME. Its usual to drill the tapped hole central of your chosen boss but on these small cylinders make sure the flange on the drain does not clash with the cylinder cover.

Don't drill the tapping size all the way through, just enough to be able to get the right depth of thread so the fitting will screw in, you can then continue the hole with a smaller 1/16" or 1.5mm drill. This small hole may need to be angled so it comes as near to the end of the cylinder as possible but not so near the end that the hole is blocked by teh spigot on the cylinder covers.

You will need to mill a flat area on te cast boss for teh drain to screw down against. also its unlikely to be tight at the angle you want so buy a set of mixed thickness soft copper washers to get teh right position.

J

Thanks guys...brilliant advice!

It sounds like the correct way to start up the engine then is to open the drain valves and let the steam pour through for a minute or so and then close the valves and allow the engine to run. Am I correct?

...also, any feedback on which side the drain cocks should be located on? Exhaust or inlet? Does it not matter?

hi matt,

i would fit them where they appear on the pic on the Stuart website on the D10.

Stuart have always used odd thread sizes with coarser threads not standard for miniature locos these days. though with cast iron you probably need a coarser thread though the old Stuart castings in iron were so good this wasnt necessary. i couldnt find Stuart listing 5/32" x 40 tpi thread cylinder drain cocks on their website. if you need to make them i am sure we can help!

perhaps give Stuart a 'phone re draincock supply?

even with slide valves you can still get hydraulic lock on starting with steam from cold.

cheers,

julian

Edited By julian atkins on 17/02/2016 01:11:42

5/32 x 40 drain cocks top of list, as I said the smallest they make.