Boiler size and gas tank size - what's the ideal relation?

kno3 · Boiler size and gas tank size - what's the ideal relation?

Most people say it is best to have the gas tank run out before the boiler runs out of water, which is very sensible (considering there's no means for resupplying water on the run).

Short of the trial and error method, is there any rule of thumb about the relation between the gas tank volume and boiler volume?

I guess it also depends on how economical the boiler design is.

My latest experimentation shows, that a 100 ml gas tank might be already too big for a 300 ml centre flue boiler, while a 40 ml gas tank is too small. However I'm not sure the small one was correctly filled, so I'd have to test it again.

spanner_monkey

I would have thought how much water was being used would be a determining factor. Dont forget the more water that is wasted the less time you can run for. So boiler water could be made to last maybe 10 or 15% longer by limiting losses such as not letting the safety valve lift regularly, taking the steam from as high in the boiler as possible to prevent priming, sealing any steam leaks and improving engine efficiency.

You could also consider using the smaller gas tank and under filling the boiler to suit, less water should take less boiling. You could set it so your gas runs out with water to spare

STEAMPROPULSION

I would start from the engine and its steam needs.
Next i would consider the boiler output an how much heath it needs to produce for that particular engine.
Next I should calculate how much gas I need to produce the amount of calories for that boiler hooked to that engine.
Unless you go into complicated calculations, there is no rule of thumb for calculating the relationship between boiler and gas tank.
Please note that each boiler and each boiler type has its own heating surface from which depends its performance and therefore is amount of calories needed.
A Yarrow is a very different boiler compared to a Center flue boiler, to a vertical multi-tubular boiler, or to a Babcock type boiler.

mogogear

In my paddler I do not adhere to this adage. I use a disposable fuel canister that will give me almost 4 hours of run time. I also use the attenuator from BIX and have a manual waterpump.

I did some bench running to determine water consumption and that gave me a big comfort zone on what I could expect on the water.

As I do not have the ability to supply oil longer than about a 30 minute run - I am forced to return to dock and drain and refill the lubricator anyway.

I do not think I could want to steam longer than a half hour.

I am starting to practice on navigation courses so it is not just the casual pond exploration but still 30 minutes is still max for me and I am OK with that - Maybe I am silly and inviting disaster but even after 30 minutes- I rarely use enough water to even require topping up the boiler.

I usually pump and refill every hour of run time- adding only about 250ml or so

The 3:1 slow gearing on the paddler and the attenuator really have convinced me of their efficiency in steam use and fuel conservation.

Roly Williams

The Hornby Rocket boiler is 68ml water capacity and the gas tank appears to be about 15 ml.

kno3

Thanks all for the opinions. Please keep in mind that this is for the specific case where pumps are not possible, due to space and other restrictions.

Roly, thanks a lot for the precise information.

After what I could find out so far, the ideal relation between centre flue boiler and gas tank volume, so that the gas lasts long enough to boil most water, but runs out before the boiler is empty, is between 4:1 and 3:1.

If anybody can provide more data, we could see if it is between these figures or not.

hellequin

Be careful as the water needs to be above the flue at all times as you probably know
The calcs should be done as suck it and see may damage a boiler
best wishes

Wallace

I use this tank here

http://www.forest-classics.co.uk/bix_mini_tank.htm

21ml capacity??

I don't have access to my run times at the moment, but approximately it will (during a 12-13min run) boil 120ml water from cold in about 2 or 3 mins, run the engine between medium/full throttle for 10mins and leave a safe amount of water in the boiler without running out of gas. Obviously the burner size plays a major part but the burner I use is suitable for the engine
I have not timed the burner run time alone but I beleive it will run the boiler dry.
Gas is good but I see the chance of running a boiler dry it's only downfall.
I now use a timer for my runs. I haven't looked into partial fillings of the tank yet but will do (ie if it takes 10secs to fill the tank, try halving it for half run time?)

Sorry, just realised you were talking of centre flued boilers

. Left this here in case it helps anyway

MrDuck

I have engines with a runtime of about 45mins so they really need supervicing rather than finding right size of gas cannister.

I would recommend that for stationaries anyways