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Hot water from the snifting valve,

not sure itís a good sign

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terry callaghan04/07/2019 20:03:09
237 forum posts
10 photos

hi all. I am having problems getting my Columbia to steam up. I have checked and rechecked the smokebox is sealed and the blower is blowing hard and so on. The water is at the half gauge mark and even after half an hour I have no pressure but a very hot boiler. Today I saw hot water mixed with a bit of light steam coming from the snifting valve, as I am not sure this is a good sign I pulled the fire. Both the boiler and the superheater have been pressure tested at two times working pressure. So is the lack of pressure linked to the water coming out the snifting valve, if so could the regulator be at fault. What do I need to check step by step.thanks

Nick Clarke 304/07/2019 20:38:06
1395 forum posts
61 photos

steam blower or electric?

is the gauge OK?

What happens if you open the regulator?

where is the snifting valve connected to?

terry callaghan04/07/2019 20:44:54
237 forum posts
10 photos

It’s on the electric blower, gauge is ok as I tested it on a second loco. The snifting valve is connected to the superheater did not play with regulator

Nick Clarke 304/07/2019 20:56:01
1395 forum posts
61 photos

Sorry - I only asked as you said it was blowing hard.

Fire - begin with wood or charcoal soaked in paraffin and then feed coal quite quickly. make certain the whole grate is covered and there are no holes in the fire.

Two areas to investigate - firstly if the gauge is reading zero it is either not making steam or the passage to a fully working gauge may be blocked and secondly is the fire burning brightly or not? If not check ashpan and grate.

If this is your first loco you could possibly do with someone else there to observe and advise as you light up - are you a member of a club?.

Edited By Nick Clarke 3 on 04/07/2019 20:57:05

terry callaghan04/07/2019 21:22:20
237 forum posts
10 photos

Hi, thanks for interest, it’s not my first loco, as I have around five. But this one I have never steamed. The blower is blowing hard. My question really was re the snifting valve, why should water be coming from it.

Nick Clarke 304/07/2019 21:38:30
1395 forum posts
61 photos

If it is fitted to the superheater water can come over if the is over full and the regulator is open (unlikely from what you have said) or from condensation - but in a modern high superheat boiler design makes this unlikely to be more than a few drops if there is a fire lit - steam is more likely than water.

You have puzzled me too. Can't offer any other suggestions, sorry, but when you do find a solution please come back here as I am now close to being as curious as you to find out the cause.

terry callaghan04/07/2019 22:10:42
237 forum posts
10 photos

Will do

Mark Rand05/07/2019 00:53:05
1239 forum posts
28 photos

Rather dumb question, but is it possible that it's caused by the Columbia design's rather exposed cylinders and valvegear? How long have you run for before concluding that there's too much wet coming from the snifters?

Edited By Mark Rand on 05/07/2019 00:54:27

terry callaghan05/07/2019 08:27:16
237 forum posts
10 photos

I have no idea at all.

SillyOldDuffer05/07/2019 09:59:24
8495 forum posts
1900 photos

I know almost nothing about small boilers in practice, but seems to me there are only two possibilities:

  1. The boiler is developing pressure but the gauge or pipework leading to it is faulty. However, ff the boiler was pressurised I would expect working the regulator, whistle, etc to emit steam. In the worst case, the safety valve should lift. (From what's been said I don't think a faulty gauge is likely to be the problem, but take care. )
  2. Not enough heat available to convert water to steam. At atmospheric pressure it takes about 400kJ of energy to raise 1kg of water to boiling point. Thereafter, it takes a lot more energy to convert boiling water to steam, another 2400kJ to evaporate 1kg of boiling water, about 6 times. Two possibilities:
    1. In the limited space available, the fuel can't make enough heat. Welsh steam coal is famously good, other coals and barbeque briquettes etc may struggle. Wood is likely hopeless. This is assuming that the fire is getting enough air; too little will choke the flame.
    2. The boiler and everything attached to it are acting like a central heating radiator and losing heat faster than the fire can make it. Try temporarily insulating the boiler and anything connected to it by wrapping the whole in several layers of Aluminium kitchen foil or a fireproof blanket. Another possibility is the blower is too powerful. Too much air forced through the fire will cool the output and reduce the time available for heat to transfer from gas to the tubes. Try reducing the blast a bit. On full-size leaving the fire-door open cools the fire, I don't know if the effect is greater or smaller on a model.

Quite likely a number of factors are at play making the problem hard to diagnose: a combination of low heat-value fuel, too much blowing and an insufficiently insulated boiler perhaps. Fix one or two and the engine might burst into life.

If not tried already, you could give the boiler a head start by filling it with boiling water immediately before firing. If that works, it means heat loss / insufficient heat from the fire is definitely the issue.

Sounds like the snifting valve is leaking slightly. My guess is that's not the problem. If the valve, or anything else, were leaking badly enough to stop pressure rising I'd expect to see a lot of steam vapour coming out of it. As that's not happening, you either have a completely sealed boiler (aka a bomb), or the water inside isn't getting enough heat.


Clive Brown 105/07/2019 12:31:20
807 forum posts
39 photos

Don't know the Coumbia design, but does the ashpan have any damper arrangement that might be stifling the fire?

Or perhaps the builder hasn't provided sufficient air hole area past the ashpan. Have you seen this loco in steam?

The discharge from the snifting valve may well be because it needs pressure to keep it closed. The regulator might be leaking slightly, as many do, allowing this leakage past the valve.


Nick Clarke 305/07/2019 13:39:04
1395 forum posts
61 photos
Posted by Clive Brown 1 on 05/07/2019 12:31:20:

Don't know the Coumbia design, but does the ashpan have any damper arrangement that might be stifling the fire?

Or perhaps the builder hasn't provided sufficient air hole area past the ashpan. Have you seen this loco in steam?

The discharge from the snifting valve may well be because it needs pressure to keep it closed. The regulator might be leaking slightly, as many do, allowing this leakage past the valve.


Terry -

Just had a look at the Columbia drawings and I have to agree with Clive's suggestions. The ashpan is very shallow indeed and the four holes in the front corners may not allow sufficient air through to the front of the fire. I addition the thermic syphon comes very close to the grate at the front of the firebox and as such may allow a hole to develop in the fire around there.

The snifting valve is pointing downwards at the bottom of a pipe from the hot header and without sufficient pressure in the system to hold it tight should leak steam if anything, but it could be water, even with the radiant superheaters the full length of the firebox.

As regards the regulator this appears to be the most complex I have ever seen drawn for a model locomotive - a twin poppet valve arrangement operated by cams. I would certainly be wanting to check that it sealed tight.

terry callaghan05/07/2019 13:46:03
237 forum posts
10 photos

Thanks for showing interest. I think that I have got all the airflow I can get around the grate area, it was not very good before. I am sure I have the regulator correct, if I blow into it and close the valves there is no leak at all. But what worries me is there is very little movement of the cam arm less then a 1/4 turn for sure. I am just unsure of how much control it would give. And it would be a total pain to get it all back in place to take it all apart again.

Dave Halford05/07/2019 18:02:01
2007 forum posts
23 photos


It may be priming if it's never been steamed before which would explain the water, but not the lack of pressure, unless the dissolving flux has allowed a tube to leak into the firebox since the hydraulic test.

FMES05/07/2019 19:38:47
608 forum posts
2 photos

Terry, I'm rather surprised that you have had this loco for getting on six years and not had any luck steaming it.

Anyhoo, lets get back to basics. its a big old lump even at 3.5" gauge and the boiler must hold a fair bit of water.

One of my locos holds about 7 litres and on a cold day 20- 30 minutes of firing doesn't always show pressure on the gauge even with a good fire going. As SOD says, it takes considerably more energy to convert hot water into steam rather than to get it to boiling point in the first place.

So as long as all of your tests have been completed properly - safety valve checks etc, then you need to wait quite a bit for the pressure gauge to start to rise even with a good fire going.

At the same time as you are heating the water a lot of expansion is taking place, and any water trapped after the regulator in the superheater for example will find the easiest way out - first easy option - the snifting valves, and this is a common release point on stream up.

Sounds to me that you may not be waiting long enough and dropped the fire before it had got going properly, there are plenty of ways to test boiler pressure indication even without a gauge - gauge blass blowdows, blower, whistle etc, so if none of these are working you get the idea that the boiler is hot but not steaming.

For mine, I normally keep everything shut off during the initial firing with just the electric blower in the funnel, dampers opened, fire door SHUT, - a common mistake that stops the draft being drawn through the grate.

I keep it like this until I see about 20 - 30 psi reading on the gauge before opening the boilers own blower, total time for the bigger engines can take 40 minutes to an hour to get to the point of the safetys lifting.

If you are totally unsure that the pressure gauge is working properly, with a empty boiler connect up some piping to a convenient port - blow down valve is good, and with the valve open feed up 10 - 20 psi of air into the system, this should make everything work (to a fashion, make sure the wheels are chocked first tho because an inadvertant regulator operation even at these pressures can cause everything to set off on its own.


terry callaghan05/07/2019 19:59:42
237 forum posts
10 photos

Hi, yes it’s been six years and I have not done a thing with it. I did however get crohns in these six years and thinks health wise went down hill fast. More even keel now so trying to play catch up. I have today tried the loco on air and found a few massive air leaks around the chack fitting and the feed tube to the right hand cylinder. I stopped the test at this point. I think you are correct in that I maybe hoping that it would come to life faster, but I have always been in a hurry. The pressure gauge was tested along with the boiler last year so I no both are ok. The fault lays with the air leaks and my total lack of patience.

Former Member05/07/2019 20:34:29

[This posting has been removed]

terry callaghan05/07/2019 20:46:14
237 forum posts
10 photos

Which it is at the moment, but not so lovely,lols

Brian G05/07/2019 20:56:03
837 forum posts
37 photos
Posted by terry callaghan on 04/07/2019 20:03:09:

...The water is at the half gauge mark and even after half an hour I have no pressure but a very hot boiler...

I just contacted my son who has steamed a friend's Columbia, and it took half an hour to get hot, and nearly an hour to reach pressure.


terry callaghan05/07/2019 21:21:34
237 forum posts
10 photos

Thanks for letting me know. An hour good god that’s some time.

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