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Vertical Boiler Fittings

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gary.a.ayres13/03/2018 09:38:02
36 forum posts
12 photos
Hi - I'm new to this forum and to the world of steam. I have begun building a small vertical boiler to run small engines. It's quite difficult to find clear simple information on the configuration of fittings on a boiler, so I have a few questions:
(1) I'd like the boiler to comply with regulations as far as possible, and understand that there will need to be two routes for getting water into the boiler. Can I just put two bushes with check valves into the barrel of the boiler side by side? Or is there some other arrangement that is recommended (e.g. different heights, etc)?
(2) I understand that the check valves for water in should be below the working water level of the boiler. Am I right?
(3) I assume that the main blowdown valve should be positioned as low in the boiler as possible ( but obviously without fouling the bottom end plate). Is that correct?
Once I have the answers I can move forward on to the next stage.
Many Thanks,
JasonB13/03/2018 09:48:30
12833 forum posts
1169 photos

If it is a small boiler you can use 1 filling point.

Yes just below bottom water level

Yes get teh blowdown as low as possible

gary.a.ayres13/03/2018 09:54:47
36 forum posts
12 photos

Jason - thanks for the swift reply! Much appreciated.

The boiler is 3" diameter and 5" tall. Will it meet the regs with just one filling point?


duncan webster13/03/2018 11:31:31
1531 forum posts
18 photos

I think the regs for loco boilers say 2 means of filling the boiler, you can plumb any numbers of pumps etc to one connection as long as they are truly independant, ie failure of one doesn't stop the other. However as you say you are new to this game, why not find an established desig and use that.

Bazyle13/03/2018 13:03:48
3946 forum posts
166 photos

BTW are you aware that the bushes need to be bronze not brass?
The 'two means of putting in water' is aimed at coal fired boilers, so mostly locos and traction engines where you are trying to avoid a sudden panic to drop the fire.. A small test boiler run probably on gas if the one pump fails you just turn off the gas.
A blow down is not essential on a small boiler, you just turn it upside down and flush it out sometimes.
The biggest issue is correct design of the material thickness and provision of stays.

There is a book on small boiler design by K.N Harris.

fizzy13/03/2018 13:08:04
1496 forum posts
103 photos

Just a screw on top to pour water in is all you need, most small boilers have no other means of filling.

gary.a.ayres13/03/2018 13:38:48
36 forum posts
12 photos

Thank you all.

@ Duncan - useful to know that I can plumb different sources to one connection - that supports what Jason said and it may be the way for me to go. I am pretty much following one of Stan Bray's designs (with a few tips from Myfordboy) but have upped the size to x 1.5. They don't say a lot about the positions of check valves, etc. though.

@ Bazyle @ fizzy - I am considering trying it with coal, small as it is. Small bits of coal! I have some nice cast iron bits and pieces to make a firebox with and the boiler will be attached to that. If the coal idea doesn't work out I'll swap it for another means of heating which I should be able to do without changing much on the firebox. I also want to hard install it all to a base, and plumb it with copper pipe. For these reasons I have bought a pump and check valves (and bronze bushes). I also feel I need a blowdown so I don't have to lift it around and tip it up. Maybe too elaborate for a first effort with a small boiler? Well, I'm not in a rush, and it will be good experience for if and when I decide to build a bigger one. We shall see how it goes...

I have the Harris book but can't find anything in it about the exact positioning of check valves etc., as per my question above. Maybe I'm just missing it - the lack of an index doesn't help!

Once again, thank you for your help.


Edited By Gary Ayres on 13/03/2018 13:39:29

BDH13/03/2018 13:48:30
754 forum posts
66 photos

Hello Gary, please remember that if you envisage running the boiler in public then an official boiler test and insurance will be required.

Even if just running it for your own pleasure it would be a good idea to have it examined and tested by someone who is familiar with steam boilers.

Do you have a model engineering club nearby? after you've paid the subs the advice is free and also probably the boiler test and insurance.

Please keep us up to date on progress.


gary.a.ayres13/03/2018 14:13:33
36 forum posts
12 photos

Hi Brian -

Yes, I'm aware that it would need to be officially tested for public use. Didn't know about the insurance but no surprise there.

I may never take it outside of my own backyard, but am aiming to build it with enough 'future-proofing' to give me a chance of doing so if I decide to.

There is indeed a model engineering club local to me, and I was thinking that I should go and see them when it comes to testing, etc. Didn't know that the subs could cover testing and insurance! Worth thinking about...

I will indeed add to the thread as the project develops.

Thanks for your advice and encouragement.


Harry Wilkes13/03/2018 14:40:19
557 forum posts
56 photos


As it been pointed out dependant on the size of the boiler you may not need 2 means of adding water and if you go the way Fizzy suggests why not still fit a bush then in the future you may want to fit a hand pump then the bush is there.

It may be worth you checking out Keith Appleton's youtube channel he does quite a lot of work with boiler **link**


Bazyle13/03/2018 18:14:54
3946 forum posts
166 photos
Posted by Gary Ayres on 13/03/2018 14:13:33:

and I was thinking that I should go and see them when it comes to testing, etc.

Club boiler inspectors really don't like people who only join to get a test as the value of their time is worth far more than the club sub. Membership Secs on the other hand like anyone who hands over money wink

gary.a.ayres13/03/2018 18:23:48
36 forum posts
12 photos

@ Harry - I actually have the pump and two check valves already, so no harm in installing them I guess. Fizzy's idea of installing a bush and leaving it as 'spare' is a helpful one though.


@ Bazyle - Heh! ... you can only please some of the people some of the time...face 23

Edited By Gary Ayres on 13/03/2018 18:26:36

Edited By Gary Ayres on 13/03/2018 18:26:57

gary.a.ayres13/03/2018 23:18:27
36 forum posts
12 photos

This is relevant (unless it has been superceded, but I have found no sign that it has):

I still have to read it properly, but so far it doesn't seem to be too specific about the type and number of fittings used (apart from a safety valve). Will post more when I have read it more thoroughly.

JasonB14/03/2018 07:30:16
12833 forum posts
1169 photos

There is a new one due out in a month or two though I doubt it will answer your questions

gary.a.ayres14/03/2018 07:48:48
36 forum posts
12 photos

Ah ok - thanks for that Jason. Useful to know.

I doubt it too, and I suppose if the rules are somewhat vague that's something to be thankful for.

Putting together all of the suggestions people have kindly made on this thread, my only remaining questions at this point are:

(1) Whether to install a second check valve for water inlet (and I probably will, given I plan to try using coal), and

(2) Where the two check valves should be positioned in relation to each other (if indeed it matters).

Meanwhile, I am inspired by this as something broadly similar to where I hope I'm going with my project:

JasonB14/03/2018 08:12:39
12833 forum posts
1169 photos

Sandyc's boiler just has the one bush for a clack valve about mid way between the two sight glass bushes.

You are more likely to need to get more water into it if running on gas than coal as it will fire better on gas, make more heat and therefore more steam.

fizzy14/03/2018 11:13:22
1496 forum posts
103 photos

Just a cautionary note regarding using coal as your heat source, your boiler has to be very well thought out and designed as compared to a gas fired one. Key to its success is the steam return velocity which usually requires quite complex calculations to ensure correct blast nozzle size and positioning and venturi. Use a proven, published design for a coal specific boiler. If im teaching you to suck eggs I do apologise.

gary.a.ayres14/03/2018 12:45:43
36 forum posts
12 photos

Thanks both.

@ Jason - yes, it does have just the one, you are right. I will think on...

The youtube clip ws intended more to convey the general feel than thedetails.

My thought has been to build something (out of two cast iron water pipe collars) that would enable me to try coal and other options before finally committing. Nothing would be cast in stone and would remain modifiable throughout. That of course would not fit with fizzy's advice to use an established design for a coal-fired boiler.

@ fizzy - you are definitely not teaching me to suck eggs! Or if you are it's because I don't know how to suck them in the first place.

Are you referring to a blower when you refer to return velocity, blast nozzle and venturi?

Gas_mantle.14/03/2018 13:10:38
322 forum posts
268 photos

I have a 3" dia and 5" dia vertical boilers and in my experience the 3" isn't really suited to coal firing, I have run it on coal a few times but it is notoriously difficult to light and then keep it burning. I've heard other people say 4" dia in the minimum for coal firing and although I'm no expert I would agree with that.

Coal firing looks easy but I find there is more to it than meets the eye, you will need a blower and ideally want the exhaust routed up the chimney, even then it's not easy keeping such a small fire box burning properly.

I've no doubt some people can get very small boilers to run on coal but personally I'd stick with gas until you are in a position to make a larger one.

gary.a.ayres14/03/2018 21:00:06
36 forum posts
12 photos

Thanks for your input, Gas_mantle. I can see why coal would be difficult below a certain size - something about the difficulty of scaling nature comes to mind. If this project goes well I do intend to build a 6 inch boiler in the future, but the 3 inch is under way, so ...

... the firebox I have in mind will be quite wide at the bottom, roughly conical in shape and quite tall. It would be quite unusual in design but the aim is to make a functional device, not to make a model of anything in particular. I'm thinking the shape could generate a decent updraught, especially with a tall smoke stack on the chimney. I have been thinking about routing the exhaust up the chimney, However, instead of a blower I envisage the gentle use of a hand-cranked fan with outlets below grate level. That would blaze up the coal, but would also be very controllable.

The system would be idiosyncratic (fine by me!) but I think it could work so will probably give it a try.  It would also look very funky in an unusual way if I get it right. However, what I have taken from these discussions is a decision not to take any irrevocable steps or commit to anything until I have tried everything out with temporary setups. If the coal doesn't work, I'll use gas instead, and nothing lost but at least I will have tried!

Edited By gary.a.ayres on 14/03/2018 21:03:22

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