boiler water volume

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

John Rudd

Well-Known Member
Joined
Oct 14, 2009
Messages
311
Reaction score
2
Is there a general rule of thumb for amount of water in a boiler?

My kids bought me a steam engine kit for my birthday recently and the boiler is made from brass ( here's a link to the kit and dont laugh!.. http://www.forest-classics.co.uk/Basic Boiler Kit.htm)
Now in the instructions itt says to fill the boiler to approx 2/3 of its volume..

The boiler is approx 113.4cl in capacity (38mm int diameter 100mm long ) so I was thinking of adding a water fill plug to one end...

I reckon that the filler plug needs to approx 10-12mm up from the c/l of the boiler...

Boiler vol= 113.4 cl
Radius =19mm
2/3 volume would be the same as 2/3 of the area of the end plate..so 1/2 full would be half of the volume or half of the area..(dividing the volume by the length of the cylinder)
As the radius is 19mm, then 2/3 would 12.6mm or so, so my filler would need to be that above the horiz c/l of the boiler and that would get me to my desired fill volume..

Does my reasoning appear right or is my logic flawed and there is some other magic number?
 
IMHO, if it's 2/3 full on the ends it's 2/3 full in the middle so just measure up from the base of the diameter of the end plate 25 mm and that is the bottom of your filler hole.

Be careful that you don't melt the rest of the boiler solder when soldering the filler plug into the end plate. One trick used by jewellers is to place almost all of it in water and then the heat only goes where it's needed.

Hope this helps.

Best Regards
Bob

 
Bob,
Thanks for your answer...Did you consider that the boiler is horizontal?
Either way I dont think it makes a difference, 2/3 is still 2/3 isnt it?
 
John Rudd said:
Bob,
Thanks for your answer...Did you consider that the boiler is horizontal?
Either way I dont think it makes a difference, 2/3 is still 2/3 isnt it?

John,

Yes I considered it horizontal and correct H or V 2/3 is still 2/3.

Best Regards
Bob
 
John's question was niggling my mind since yesterday evening....

On a horizontal boiler it does actually make a difference, and the 2/3 volume marker does not lie on 2/3 of the diameter, as the volume changes non-linearly.
The length of the boiler remains constant for the volume calculations, but the area of the circle segment formed by the water level plays a role.

I wasn't going to go through all the math to work out where the 2/3 volume level would end up, so I stuck all the formulas in the attached spreadsheet and did the calculations.

It ends up to maintain a true 1/3rd steam volume space, the filler plug must be at 24mm - not much of a difference ;)

Kind regards, Arnold




View attachment circlecalc.xls
 
I usually fill my boilers with a 60cc/2oz syringe, fill to the top then withdraw some.
Regards,
Gerald.
 
Arnold,

Thanks for verifying my calcs...Good job I didnt drill the hole in the end plate!

I had a clue that the volume would be non-linear due to the area of the 'circle'..But I just got all muddled up going round in circles....lol :)
 

Latest posts

Back
Top