Not enough steam

[jamespetts]

After a number of modifications from last time, I ran my Stuart Score and 504 boiler again to-day (photographs and video to follow). Despite the fact that I had re-lagged the boiler with an second sheet of kaowool and an outer copper shell, adjusted the burner so as always to get a blue flame with light blue cones and a glowing red surface, and raised it to just below the water tubes, I still did not get much in the way of steam production.

When I was running the engine even at a really very slow pace (slow enough that very light pressure on the flywheel could stop it easily), the boiler was not maintaining pressure, and it would only ever increase pressure when no steam was being used at all. Running the engine with the valves fully opened dropped the pressure to almost nothing in less than a minute. There were no leaks in the boiler itself or the fittings (once I had tightened them, in any case), and only very small leaks in the steam glands and at one place in steam pipe to the engine.

I have yet to lag the main steam line (I waited to check to see there are no leaks), which should help a little, but that would not be enough by itself, I should have thought, to make that big of a difference, even in to-day's cold weather. There was, at least, no soot on the water tubes this time.

I was wondering whether the problem was related to how far into the firebox that the burner is: presently, the back end of the burner is just underneath the lowest part of the pipes, which is at the chimney end of the boiler. The burner does not go all the way to the other end of the boiler, so there is a fairly large area at the front (at the opposite end to the chimney) that is not getting heated directly at all: indeed, it is getting cold air rushing in from the front air inlet to feed the fire further back, the hot air from which is then going straight up the chimney.

Do people think that moving the burner back further into the firebox would help, or would that then cause problems by taking the heat away from the lowest point in the water tubes? Any other suggestions?

[steam4ian]

G'day James.

Do some googling. Look out for boiler Babcock and Wilcox to see a diagram of a full size boiler of which yours is an imitation. Not that the grate and fire are at the front and that the hot gases pass along the boiler. Have your burner at the front near the fire doors and make sure the flames pass along the boiler. The flame is hottest at about half way out from the blue cone/s to where you can't see it in dull light. Remember, a lot of heat is transfered by the bottom of the boiler barrel; there is some argument regarding the usefulness of the tubes on small boilers.

Have fun
Ian

[jamespetts]

Ian,

thank you for your reply :-) I have seen the diagrams of the Babcock & Wilson boiler designs, which, of course, were originally intended for coal firing. From my understanding, gas flames cannot very easily be made to heat anything other than the space directly above the burner, even with draught, so using the same system as for a coal boiler (where the flames are much larger and more readily moved with draught) may not work effectively.

I have measured, and found that the boiler barrel is about 28cm, and the burner only about 14cm. One thought that had occurred to me was to add a second burner at the other end of the boiler to fill the dead space there, such that all or almost all of the underside of the boiler is being heated directly by a gas flame; does that seem sensible?

[lancelot]

Hello James, just as a suggestion,... could you obtain the correct ''Meth'' fuel burner for your boiler and try it as an experiment, see if it gives a better steam production...looking at your running of the engine under steam, what pressure did the guage sit at to run engine, what did it achieve before letting steam to engine... Personally I think you should insulate with wooden lagging rather than metal ... have you checked the engine itself, i/e piston seal for loss of power...I have no experience of running with Gas, but on my initial trial run boiler blew safety at 65 lb/'' then proceded to demolish Plastic pipe connection on engine, so plenty of power there... just need to get a Few bits sorted...
All the best for now,
John.

[jamespetts]

John,

thank you for your reply :-) I already have the original burner: it came with the boiler. I have not tried it yet (the steam exhaust line to the chimney would make it awkward to fit it in). I might try that if I cannot make any more progress with the gas, but I should like to keep it pristine as long as possible: it is really rather old, and quite something that it should be unused!

As to how the engine worked in practice, see the video posted in this thread for more details. When no valves were open, the boiler did, eventually, achieve its maximum pressure of ~60psi, and blew the safety valves, although that was fast depleted when the engine was run, and took a long time to build up again, even with the main steam valve fully closed. It would take several minutes, for instance, for pressure to go from 25psi to 60psi with no steam being used at all. Conversely, the engine, running at full speed, would run the boiler down from 60psi to 25psi in 15-30 seconds or so (these are estimates, as I did not take exact timings).

What boiler were you using that blew its safety valve at 65psi on your trial run?

Edit: As to the lagging, only the outer shell is made of metal: the insulation itself is provided by kaowool sandwiched between the outer shell and the boiler itself.

[lancelot]

Hi James, Boiler ...Babcock 504...same as yours, on trial there was no insulation on the top of boiler nor on pipes...when I am able I intend to lag the boiler with ceramic sheet and wood strip...(cadged a box of coffee stirrers at Mc Donalds) ;D ...the pipes will also be lagged.
I watched your video, Very good not a leak visible, wish you could have seen mine, Sauna bath time...would there be any heat loss through the metal cladding?
I will be running the 10V and the Score Isolating each one. I will run the smaller one first then the Score, you are talking of powering two 3/4 '' bore cylinders, so I myself wonder if it will be effective...we will just have to see.
I still think , try the meth fuel way.
All the best for now,
John.

[ron]

James, there is something wrong somewhere with the firing, the gas burner should bring the pressure up very quickly if there is no steam draw, I ran mine initially with meths which as I've posted before I found a bit uncontrollable, with a gas ceramic burner I can quite comfortably run a Victoria [1" bore] continuously and a No 9 [1 1/2" bore but still tight] for shorter periods. I didn't find the position of the gas burner critical but with these very small boilers and engines even the slightest thing amiss affects them badly. It is also worth making sure the engine is A1 100% OK, the slightest mistiming or tight spot has a very big effect on their performance. I found even nipping the packing up had a remarkable effect for the worse even if it was slightly too tight.
These small steam plants take a fair bit of practice and patience to get them to run well, they're not like IC engine that you just start up and run! Try starting the engine at a slower speed on partial valve opening and try and maintain this speed to get a feel for what it can do.
Ron
PS I don't think yout displacement lubricator is near enough to the engine and you must be loosing a lot of heat through the unlagged pipes.

[steam4ian]

G'day James.

I still maintain you are firing from the wrong end. You said that combustion air has to come along the boiler before reaching the flame, this i cooling the boiler. Gas flames may be shorter than coal but this is no reason for sticking the burner under the chimney.

regards,
Ian

[jamespetts]

Thank you all for your replies - as ever, most helpful and illuminating :-) Lancelot, is there any chance that you could send/upload videos/photographs of your successful firing (concentrating on the burner) so that I can see what it looks like when it works? As to heat loss through the metal cladding, I don't think that there would be much: it is on top of two sheets of kaowool. Water running on the top does not get hot enough to boil.

Ron, it does take some time to build up steam with no steam draw, so I shall have to look into the firing issue again. I am wondering whether there is a leak between the incoming gas pipe and the jet ring (when the fire blew back in the wind on one occasion, a small yellow flame persisted at that join until blown out). I could try sealing that with PTFE tape to see whether that makes it better. The engine does have a noticeable tight spot, but that wouldn't affect the speed at which steam pressure builds when the engine is not running, of course. I will also try lagging the main steam pipe before I try it again. As to running the engine on a slower speed, as in the video, even running it slowly depleted the boiler pressure. As to the displacement lubricator, I read somewhere that it mattered not how close that it was to the engine - it will put the oil in the steam line, which will travel to the cylinders, one way or another.

Ian, I shall try putting the burner at the other end of the boiler next time and see whether that helps. If I do that, do I need to make any consequential amendments?

[Tel]

Yeah, I must admit I'm a bit puzzled as well James. Just where are you putting the burner in??

Over the years I have built three of the 'Monarch' Steam plants, the boiler of which is just 4" diameter and about 8 or 9 inches long - centre flue with four cross tubes. Fired with just an ordinary gas torch, the sort we use in the workshop, these things will generate enough steam to run 3 or 4 engines at the same time.

In any event, the burner needs to go in at the end furthest from the chimney (unless it's a Scotts Return) so that the gasses pass the entire length of the boiler - anything less and you are just spitting into the wind.

[Tel]

Sorry about the blurry image, but that's the burner poked just inside the centre flue - neither the boiler nor the pipes are lagged

[tbsteam]

I don't know whether this could be any help but a couple of years ago i had a old steam tug with a mamod set up in and i got it going one day and when i put it in the water it wouldn't move as there wasn't enough pressure and the problem was the safety valve was leaking but wasn't visible that it was leaking.

[jgb7573]

Hi James,
Good to see your score running. If you're not doing so already, one thing you might consider is filling the boiler with hot water from the kettle. That should help get up to pressure a bit quicker. Also use hot water when you replenish the water level using the hand pump.
I also think you would have more success on a warm day! Could you negotiate with your dad to try running the engine indoors? ;D
Given the time it takes for the boiler to get back to full pressure after running the engine I think you're right in concentrating on how to get more heat into the boiler. If the burner is shorter than the boiler, is there any chance of using a longer ceramic burner? That way you'll get direct heat onto as much surface area of the boiler as possible. The efficiency in terms of the amount of gas burnt won't be as high, but I'm assuming that the fuel cost is not the most important consideration here. The leak from around the burner joint should not affect the amount of steam produced, but by all means try to stop it if you can. Finally in these ramblings, I see you are using butane with some added propane. I don't know the answer to this but I wonder if this fuel has a high enough calorific value? I know we use propane on its own for our blow torches. Does anybody on the board know about this?
Best wishes James. Have lots more fun.
John

[Tel]

OK James, I've just had a look at your pics - the end where the pressure gauge, water glass etc are is the 'driving' end, and it is WHERE YOU SHOULD HAVE YOUR BURNER.

[lancelot]

I hope ''Mike'' does not mind me pulling this shot from his ''Archives''...( it is to blinking cold to go to the shed and take photos)

I would tkink this shows which end the burner goes in

[Tel]

.... the difference being that that clearly ISN'T a gas burner, where the flame, and heat transfer behave quite differently

[lancelot]

Hi Tel, took the opportunity of pulling this one from the archives as well, also spoke to ''Stuarts'' who tend to agree that the boiler is fired from the ''Chimney'' end in Both cases...

All the best for now,
John.

[Tel]

Now that just doesn't make sense to me mate. Sort of like mounting the pressure gauge and water glass of your loco on the smokebox door, if you see what I mean. Having sat through quite a lot of 8, 10 and 12 hour 'runs' with the wheels turning non-stop, I wouldn't even consider the use of a boiler that had to be operated 'from both ends' as it were.

'Real' Babcock boilers were fired from the business end, and that, in my opinion, is how it should be done.

Seriously mate, take a good, long look at that second pic of yours, and tell me how practical it really is? OK for short runs and 'plays' at home, but that's about the limit.

[havoc]

Just a few toughts:
- sure your burner is working correctly? Like the jet being clogged... I have once spend time wondering why my loc needed more time to build pressure, deplete the boiler and then restart. Turned out to be a clogged jet. Try to blow backward through your jet with a bycycle pump.
- like Tel says: re-arrange your burner. Don't put it higher, this doesn't always help because the flame needs to have space for full combustion. Too close and you don't get maximum heat.
- if using butane, are you sure that your tank doesn't get too cold and you're losing pressure?

[ron]

Using a gas ceramic burner with the 504 I stick it in the 'business' end ie where the pressure gauge and fittings are, I've blocked up the gap at the other end where the old meths burner used to go in with a piece of 1/4" hard asbestos , the burner is on the deck [ie not raised up nearer the tubes] and the small gaps at the side are left open to supply combustion air.
The ceramic of the burner is approx 5" X 2" and sits under the opposite end of the boiler from the lum, this works a treat but I didn't find the burner position all that critical, I also normally fill with hot water as it's quicker and cheaper.
Ron