Soldering/brazing a boiler.

I am building the Midwest Steam vertical boiler. I am hoping it will produce enough pressure to power my 3BIM and 7BIM engine from PM Research. I require some advice about soldering the boiler.

1. I will be soldering the ends first then I will add the chimney then the boiler fittings (filler cap and steam outlet). I am worried that when soldering the chimney and boiler fittings that this will undo the ends which will have already been soldered. Should I be concerned about this and how do I get around it ? I was think of using a much smaller propane torch for the later stages.

2. The small hole on the top left of the boiler is for a 1/8 inch pipe to be soldered in but I intend to replace this with a 1/4 inch boiler fitting with a 3/16 adaptor. You can see them sitting on the block of wood on the left.  Any comments on this plan ? Update : I have just found a 3/16-40 boiler fitting in my plumbing box so I will use this instead.

Edited By Brian John on 31/10/2014 03:08:20

Edited By Brian John on 31/10/2014 03:18:02

Edited By Brian John on 31/10/2014 03:18:50

Brian, what solder do they provide in the kit, I think its just soft solder rather than silver.

If you solder the top first, then stand it as you have it now to do teh bottom & fittings they should not move. You may need to pack up the chimney so it does not drop through but the other parts won't move.

Is the right hand hole just a filler with cap? if so you will have to add a safety valve as I think the idea with this boiler is that if the pressure gets too high the flexi hose will just pop off of the 1/8" pipe which gives the effect of a safety valve. This won't happen with threaded fittings

.

Jason,

I know next to nothing about model boilers, but, that seems a remarkably loose interpretation of a 'Safety Valve' ... It appears to be almost designed to give the operator a face-full of Steam ... do they really get away with it ?

MichaelG.

Apparently so

Brian. A video on youtube may give you more detail on your Midwest boiler construction.

See Here

Mike.

That one has added a safety valve due to using rigid pipework. And looks to be soft solder

I think these boilers are desisgned for use with small oscillators in mind. So any excess pressure would push the cylinder away from the port face.

But if they sell the boiler kit as a stand alone product, then they should provide a safety valve.

I would recommend drilling the top cap for a safety valve bush if you havn't already.

If you intend to use this with non oscillator type engines, silver soldering it may be more suitable. Without knowing to much about this particular boiler, other than what can be gleaned from the video above, a max working pressure of 10-15 psi would seem plenty.

I built a small boiler not so different to this one and it runs at a max 15psi, plenty for most small engines.

John

1. No solder is provided with the kit. I have purchased the correct silver solder and flux from a model engineering firm.

2. Yes, the boiler is designed to run the small oscillating engine (provided in the kit) which I am also building. This requires some soldering of the brass parts as well so it will be a good learning exercise.

3. I had not considered a safety valve but it seems like a very good idea. Would a 30 pound safety valve be okay ? This is over twice the working pressure.

I see that Mamod make them :

http://www.ebay.com.au/itm/1-4-Standard-Long-Safety-Valve-For-Later-Mamod-Live-Steam-Engines-Models-/231291068850?pt=UK_Trains_Railway_Models&hash=item35da05a1b2

Edited By Brian John on 31/10/2014 09:46:39

I think it would be a very good practice to silver solder your boiler Brain and to also fit some form of simple safety valve. But if you only need 15psi - why not set the safety at just above this (and not twice)?

IanT

Okay, I was confused with boiler testing where they run it up to twice the working pressure.

How do you know what the safety valve is set for ?

By fitting a 15psi safety valve you are restricting the working pressure to just that 15psi, if you fit a 30psi safety valve the boiler has the potential to reach that given enough heat/time.

The design of the boiler would dictate it is only intended for low pressure applications. With a single flue and no additional bracing, fitting a 15psi safety valve would be well within the boilers design limits. Best to be on the side of caution with any boiler, no matter how small.

Testing of boilers is what may have you thinking about doubling the numbers, this is done at twice the max working pressure.

John

Damn my slow typing!

Edited By John Bromley on 31/10/2014 09:50:59

You can buy safety valves with preset blow offs.

Dream Steam sell them.

John

Brian,

Heres a link to a forum thats had a bit of interest on this boiler **LINK**

I think its really for the little oscillating engines rather than the bigger ones that you have built.

Still, its a nice little project to get started with.

Lofty

Mamod offer two steam pressure valves : for older and newer models. They both have a thread on them. I do not think they would screw into the top of my boiler so would it be okay to solder them in ?

I read the above link and he used wet rags around the ends of the boiler to prevent desoldering of the ends while he added the fittings. This is a useful idea.

Edited By Brian John on 31/10/2014 12:56:13

Brian,

You DO NOT 'run it up' to twice working pressure, its should be tested hydraulically so there is no chance of a dangerous instance if anything fails, the safety valve should be set so that pressure does not exceed 10% above normal operating pressure.

I'm not to sure how these regulations would apply to a little pot boiler like this as you have no pressure gauge to set the safety valve to, or sight glass to monitor the water level, ( the regs say that a water level indicator is not necessary as long as the supplied fuel runs out before a dangerous water level is experienced.

Boiler test code for info **LINK**

I am a bit confused now as I thought that these smaller pot boilers did not require a safety valve.

There is no safety valve on this is there ? Should it have a safety valve ?

**LINK**

Would the Mamod standard safety valves suffice for these pot boilers ? They are set to about 15 PSI and have a 1/4 -26 thread (BSF).

The fact is that what you do in the privacy of your own home is pretty much up to you Brian. But as pointed out in an earlier post, relying on the pipe "blowing off" may work in practice but will be messy and could result in scalds.

So, it would be very good practice to fit a safety valve and I imagine that the Mamod valve would be a simple solution in this case.

Regards,

IanT

Mamod safety valves (1/4 BSF 26 TPI) and bushings have been ordered this morning but will take one month to arrive from the UK. I have order one short and one long ; both are the same size so either should work.

Can anybody tell me what size hole is required to take the boiler bushing for the standard Mamod safety valve ?

No but if you are going out to buy a drill bit for the bush you may be better off getting a "step drill" as its les likely to snatch when you drill the copper.

J