Stuart Triple new build

Steamchick said:

Hi John, Thanks, a great blog site you have. I just cou;dn't figure how to post comments - that you need to support the site.
But here are some tips of what I do - which may or may not suit what you are doing. You take what you need and discard the rest!
First, Lagging.
I reckon you can lose of the order of 5psi of steam pressure by not lagging your steam pipes. Polished copper makes things "pretty", but if we are showing off "Engineering" then we should be managing heat better. I lag my steam pipes (NOT the syphon tube, or cold pipes) by winding cotton string around the pipes. It takes time and care, but you modelling shows you understand that. When finished, the cotton is painted with white emulsion paint. It then looks a lot more like a "Proper" engine room set-up, and has the advantage that the boiler needs a few psi less pressure to run engines about the same speed. You can lag the manifold (Steam fountain) as well if you desire, as otherwise you are simply condensing steam before it feeds down the main pipe.
Next: The fire:
I worked where calculations of radiant heat were daily considerations. Inside your boiler you have a nice flame fire from the burner. But you can improve the heat transfer CONSIDERABLY by adding a radiant element inside the firebox. I.E. LOOSELY compressed wire wool - I use stainless steel pan scourers as they are cheap and good stainless steel wire. I have also used electric element wire from old electric heaters that simply have resistance wire that glows red hot.... It lasts forever, almost! Once you have seen where the fire heats some wire wool red hot, you can even have fun making a shaped wire wool element to just fit in that part of the flames. What this does is take hot flame energy and broadcast it to the walls of the firebox, and into the water for boiling and steam. Then the flue gases are a bit cooler, and less dense, so the flue can take more exhaust... = a bigger fire! There will still be plenty of hot gas up the flue to the chimney stack. Ideally, the bottom of the chimney is only 20degrees or so above steam temperature, for an efficient boiler. I assume (Which makes an "ass of me") that you are superheating the steam, as all you want the steam to do is carry heat through the engine, not condense until you reach the condenser... even though some will as it expands and cools.
Boiler lagging. Underneath the gorgeous wood lagging and brass banding, I guess you have some conduction barrier - matting - or something? As a check, how hot is the outside of the boiler? I can comfortably just warm my hands by wrapping them around the lagging, no risk of burning the flesh, as I have "good" insulation. I use an aluminium foil sheet glued onto the copper boiler. Wrapped in a mat of conductive insulation. (I have used proprietary stuff, also COTTON flannel, a piece of an old WOOL garment, corrugated cardboard. Then another sheet of aluminium foil, covered in a nice vanished wood cladding, or aluminium casing, or whatever. The 2 layers of foil separated by conductive insulation, form a radiant insulator, that stops more heat escaping than the wood cladding can. I demonstrated this recently, when firing an horizontal boiler, where a part of the boiler was yet to have cladding fitted. The clad part was at over 100deg.C. the unclad part 135 deg C as was the steam inside the boiler. Until I covered it with 2 layers of foil, a bit crinkly so there was a small air gap, when the thermometer showed only 30 deg.C on the outside! Made a big difference to the quantity of steam produced as well! Colleagues were amazed!
Superheating. The aforementioned boiler I was firing had about 8 inches of a single (1/4in bore pipe) tube in the fire (Very hot!), but a colleague has done calculations, and it really needs up to 5 times that to have a "proper" rise of steam temperature (not pressure) in the outlet pipe, when in flue gases, not the fire. I have a 3 in boiler, with a steam pipe fed through the fire, with nearly 2 ft of tube in the fire (coiled). Suggestions are for the superheater to have up to 80 times the bore diameter of length when in hot flue gases, post-boiler. In a triple expansion engine, you'll run a lower steam pressure with more superheat.
The engine. I see it has auto-drian valves on top for prevention of hydraulic locking when worming from cold. I guess also steam (condensate) drains on the bottom cylinder covers? Otherwise the hydraulic lock when running-up from cold will blow the con-rod glands, whatever they are made from. I find on a twin expansion engine, that the drains open, I can hand crank the engine for 5 mins or so before the condensate is almost down to a drip or 3..., when it will just start running with drains open. Then when I close the drains on the HP stage, the LP stage takes a further 5 mins or more to warm-up. Even after closing the drains on the LP cylinder I run at about 12-15 psi before the LP starts to work, when the revs rise noticeably! I can then drop the steam to around 10 psi when the engine will idle about a similar speed to your show demonstration. I guess you find something similar as your engine warms-up? Considering it is really just a single cylinder engine when staring from cold, (Insufficient hot steam to IP and LP for then to do any work) I think you lack of self-starting in one video is simply a cold engine? - But you are right in that a difference between forward and reverse speeds at the same steam regulator setting is indicative of a valve timing glitch. (Assuming you have low friction in the cross-head slide when running in both directions).
Finally, I like the gauge glasses with a built-in red line - make the water level very clear - or use a card behind with 45 degree lines. They reverse direction at a certain optical distance from the glass where the glass is full of water.
I hope some of these ideas are useful?
I do wish I had the patience and skill to make such good looking models as yours! What I make is truly crude by comparison!
K2

Click to expand...

• A 3 1/2in Tich - belongs to my club - recently inherited from a recently passed member. ("passed-away", as well as "past"). Out of respect for his fine workmanship, I am in the process of servicing it prior to getting it re-certified and running again.
• 3 of my boilers - needed some mods, and re-certification, as the COVID lapse of certification means they are now considered "New" and needed bringing to today's standards for calculations to be acceptable.
• A new gas burner for a Club boiler, to increase the power available - due for the next Annual re-test. (A new steam test required when I finish installing the burner).
• A steam pump - Half-built but not touched for a year due to other jobs jumping ahead in the queue,
• A small Mamod bench boiler - with feed-pump, etc. making it a "proper" set-up for continuous running, not just the toy "fill and run till empty" strategy. I want to run a 1in bore and stroke DA engine at up to 15psi with my "improved" heating strategy. POSSIBLY it can run your triple expansion engine (at no load)? - not just a little Mamod oscillator.
• An improved superheater for the Club's "Stuart" boiler, that was recently brought back into service and has a more powerful gas burner to run a Tesla Turbine. The original burner was about 0.8kW (Gas power) - replacement ~3kW... Stuart certification of 60psi was not available for traceability so the Inspector insisted I do calculations - that meant adding stays so it can be certified at 30psi. (As a "new boiler" - for 2018 regs!).
• And 2 steam boats, another stationary boiler, etc. all need servicing and new certification... and I must make 2 hand feed-pumps, valves, fittings etc.
• And a Super-Simplex boiler needing a repair and re-certification... and maybe a gas burner?
• Then I can get back to planning how to combine a boiler with a Stuart SUN engine and generator I made previously...? ...etc.