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Boiler water level

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Speedy Builder522/09/2021 20:04:05
2407 forum posts
191 photos

Where should the boiler water level be on a 5" SPEEDY loco. Ie, how much higher than the crown of the firebox.


ChrisH22/09/2021 20:26:24
1003 forum posts
30 photos

Standard for most boliers I know of, though I don't know about loco boliers, is to run the boiler with the water level showing at halfway in the gauge glass..

Bazyle23/09/2021 00:24:41
6038 forum posts
220 photos

But I think he want's to know where to set the glass wrt the crown of the boiler so that mid point is a sensible level, and obviously bottom nut adequately above crown. You really need the boiler drawing. You also need to allow for inclines and surging.

Paul Lousick23/09/2021 01:07:49
1855 forum posts
661 photos

Our boiler code in Australia states that the bottom (visible) end of the glass shall be above the crown of the firebox by not less than 10% of the distance from the crown to the outer wrapper.

Speedy Builder523/09/2021 06:51:58
2407 forum posts
191 photos

Thanks for that, that's a definite for the bottom of the glass, now need the level, as I don't know if LBSC's designes matched todays standards for the mid point. There is nothing in his book or drawings indicating levels.


Paul Lousick23/09/2021 09:14:34
1855 forum posts
661 photos

I can't comment on a Speedy Bob as I drive traction engines, model and full size and keep the water leved around 1/4 to 3/4 of a glass but it does depend on if you are going up or down a hill. The change in gradient is much bigger on a traction engine than on a rail loco. Not enough water in the boiler and you expose the crown and it can melt. Too much water and the engine will prime and break something. Reading the road ahead and having the right level of water in the boiler comes with experience. Running on a level club track is much easier and you should not have any problems.


noel shelley23/09/2021 09:47:13
758 forum posts
19 photos

Paul posts are right ! If you do not have the drawings and can't get them Then Pauls guidance is good ! Bottom nut / glass 1/4" above crownsheet, top nut as high as is practicable. As it's a locomotive the running level is fairly steady so mid glass as a running level would be good, only experience will show the safest and best level to use to avoid priming, which if using piston valves is not good. Good Luck. Noel

Paul Lousick24/09/2021 00:29:04
1855 forum posts
661 photos

Noel, I am confused about you statement " Bottom nut / glass 1/4" above crownsheet"

Our code states that the bottom (visible) end of the glass shall be above the highest point of the crown of the inner firebox by not less than 10% of the distance from the crown to the outer wrapper.

On copper boilers the top of the fusible plug has to be a minimum of 6mm above the crown and on steel boilers 10mm above the crown. If the water level was down to the bottom nut at 1/4" above the crown, they would be exposed.

Bazyle24/09/2021 00:59:02
6038 forum posts
220 photos

So use 10% or 6mm whichever is greater. It may depend on whether you are building to a published design as agreed by an UK boiler inspector or the newest Australian rules. A bit of common sense is required for the top as it will also be affected by the presence of a dome and type of regulator as to whether it will prime and the owner will get used to how it behaves.
Incidentally when you hand over a loco in steam to another driver it is common courtesy to mention if it tends to prime easily below a full glass, just as you would mention the levels of the fire, oil and water tank.

Speedy Builder524/09/2021 06:53:40
2407 forum posts
191 photos

This is a bit of a busy copy of the beachhead. (Backhead)

The distance from top of crown to inside of wrapper is 2 1/2"

The centres of the water gauge fittings are 5/16" from the inside of the outer wrapper and then 2 1/8" appart.

Distance from end of union nut to centre of fitting is 7/16", Visible glass length 1 1/4"

backhead drg.jpg

Luker24/09/2021 07:45:11
81 forum posts
87 photos

Hi Bob, I can't help with your specific boiler but with my designs and builds I use the 10% rule as mentioned previously from the top of the inner firebox rapper (works well and you have ample time to recover a boiler). I've found the sweet spot for most of my boilers to be with a steam volume of roughly 10%, and where practical this is my mid-point of the sight glass. I wouldn't be too pedantic now on running at an exact point, as the level does move a little on steam (especially if the sight glass holes are too large) and unless you get a lot of track time in you probably won't notice much difference.

As to the fusible plug: I personally don't install them on my class 0 or class 1 boilers, but then the crown is designed to run dry, and the grate can be easily dropped. This is of course dependent on the local bureaucracy.

The speedy was a successful model, we have one that has run for years…

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