Boiler terminology

I was researching info and designs for a small boiler safety valve when I came across an old post in this forum by Stub Mandrel. He was describing a problem with a sticking valve he was testing.

He wrote:

"I gingerly prodded the top pin of the safety valve to see if it was stuck and 'wham' a huge jet of wet steam hit the ceiling of my workshop, presumably as it primed. I lost 1/4" of water in the glass but it stopped wjhen I turned the gas off. A repeat outside saw the same., except teh geyser was about 12 feet high and created a localised shower downwind, much to the cat's alarm. It didn't close again until the pressure was nearly zero."

What does he mean by "... presumably as it primed..." ?

Our North American brethren would call this 'foaming', which is a much better term. See article at

**LINK**

for a good description. It often happens in new boilers, the residues of flux etc seem to set it off. Seems to settle down after a few changes of water

Thank you, Duncan. Interesting read, and it answered my question.

I have, what I believe to be a domestic steam heat radiator relief valve. I found it in my Dad's tool box. I fugure it's got to be 75-100 years old. The coin in the picture is an American Quarter for scale. I would like to make one like it but a bit smaller to use on a model boiler. Think it would work? I intend to make the valve and body long enough to give a good range of adjustment.

Ha, I can confess to knowing Stub Mandrel's mind on this...

Priming is when boiler water is carried over with the steam.

In this case popping the safety valve manually on this small boiler reduced the pressure in the boiler enough to cause a significant amount of water to turn rapidly to very wet steam which then exited via the valve carrying lots of water with it.

It was quite fun to watch, even though it wasn't quite what I wanted to happen.

Neil

I have been drawing up a set of boiler fittings for my first build. As I'm a yank, I am designing/drawing in imperial and using UNF threads.

I have Stan Bray's book, Making Simple Steam Engines, and will probably build my first boiler from the plans in that book.

This afternoon, I made an attempt at making the safety valve from that book. Below is a picture of my attempt. I've decided on 1/4"-28 thread for my various fittings. I used the spring from a 'clicker' ball point pen, and a 4.75 mm ball from a cut up ball bearing. I did not make the guide rod as in the book. Do I really need it?

The adjustment screw is long to make sure I can adjust the valve to the working pressure that is yet to be determined. What do you think of my attempt?

Looks good. Where does the steam escape? Holes yet to be drilled, presumably?

I never heard priming referred to as foaming in the seven years I worked as a licensed boiler engineer in the USA (Montana). But dialects vary with region over there. Foaming, in my recollection, referred to a lesser form of carry-over of bubbles coming off the surface of the boiler water due to contaminants in the water. Priming is actual drops (in large quantities) of water being carried over. Quite exciting on 24" diameter pipes etc. Like cannonballs going down the lines, which dance around like strands of spaghetti. A sight -- and sound -- never to be forgotten. Foaming can be more of a silent killer. I was on a crew that had to repair a power station turbine after the operators let the boiler alkalinity get too high and caused foaming. The force of the tiny bubbles of water that managed to get through the superheaters and into the turbine blades generated enough end thrust to burn out the thrust bearings, a white metal arrangement several feet in diameter.

But I think you'll be all right with your smaller version! You are in good hands with Stan Bray. One of the greats.

Edited By Hopper on 14/09/2018 12:01:00

Per the drawing in Bray's book, there is a 1/16" hole through the knurled screw.

This may not be the place to ask, and please point me to the correct forum if not... Obviously, I'm researching info to build my first boiler.

I have a few books on boilers and have learned a lot from them and from asking questions here. What I haven't yet found, is how to determine the steam requirements of a specific engine. Or, stated another way, how to make sure I build a boiler big enough to run my engine?

As I can't, or haven't yet, found a source of copper tube of decent size to build a large enough boiler to run all the engines I've built, I will probably build Stan Bray's double tube boiler.

Being a very curious fellow, and wanting to understand the why, as well as the how, where can I find the calculations necessary to determine how big a boiler I need for a specific engine?

Ah. Didn't see the hole up the threaded spindle. Good idea!.

Don't know of any hard and fast calculations for boiler size for models. There are many variables, such as fuel type, tube design etc. Also, if you have a feed water pump you can use a smaller boiler and keep filling it up. If no pump it's maybe good to have a bigger boiler for a longer run. It does not take much steam to run most model engines, specially if you just want them to chuff away at a reasonable approximation of the speed they would have run in real life at full size. Mine will happily run on 5psi. It's a good idea to run the steam line through the firebox as a bit of a "superheater" to dry the steam before it reaches the engine and to use a throttling valve right on the boiler shell to reduce the steam pressure from main boiler pressure down to working pressure for the engine. Gives a nice dry(ish) steam that will run an engine quite economically.

Stuart models have sold a number of boilers and boiler kits over the years to power their engines. So making something of a similar size should work OK. Also ME magazine has been running a series on building a vertical boiler in recent months. Maybe of some interest.

I've always used the book by K.N.Harris to work out this sort of calculation. The amount of steam required can be arrived at by taking the volume of the cylinder and multiplying it by the number of strokes per minute (and doubling it if the engine is double acting) Then steam tables will give the amount of water to turn into steam.Then the heating surface of the boiler can be calculated.

Brian

One thing that will cause the safety to eject a quantity of water is if the boiler is over full/not enough head room, or if the threaded end of the safety valve protrudes too far into the boiler, there needs to be room for the agitated surface of the water.

Ian S C

Brian, I am re-reading the Harris boiler book and taking notes... I found what you referenced. Thanks for the re-direction. I knew I'd seen it before, just couldn't remember where.

Ian, thanks for the input. I've learned so much here...

I will continue my studies of model boilers and their function, and hopefully will build one soon.

Chuck The ball would have been better had it been stainless ( rustless )

Roy

I believe the ball is stainless, it came from a ball bearing...

Very doubtful.