What vacuum gauge for testing smoke box vacuum?

Hi,

I have a 3 1/2" County Carlow that is not drafting that well and so I wanted to connect a vacuum gauge to the smoke box and play around with the blast nozzle size to see if I can improve things.

I have no idea how much vacuum will be there and so I was just after an idea of the expected vacuum so I can get a gauge with the correct scale on it.

Any suggestions?

Thanks,

Greg

Edited By Greg H on 22/08/2016 13:09:19

Greg,

I think a simple water manometer tube would be the best bet.

... Angled, if needs-be, to increase sensitivity.

MichaelG.

.

Edit: This explains

http://www.engineeringtoolbox.com/u-tube-manometer-d_611.html

Edited By Michael Gilligan on 22/08/2016 14:07:28

I suggest you take a look at the John Baguley (sorry if I spelled you name wrong JB) website and read up on draughting design. I changed mine as per JB's info and it went from placid to a complete roaring inferno!

The maximum possible vacuum is about 15 psi or 1 bar. So, an easily found car inlet manifold gauge - as used (but rarely understood) on tune-ups, etc. But as you are only expecting a slight vacuum (I guess) a manometer is even easier. All you need is a length of see-through pipe and some liquid.

Water is the easiest to use, but do be careful to avoid the water getting into anywhere hotter than boiling, or sensitive to rust. Obvious, really, once you have got it wrong ...

Cheers, Tim

Same problem, different questions !

Will an air line tapped into the blast pipe give the same results as steam?

And, will a continuous 'blast' provide the same ' best position ' as an intermittent supply i.e. engine running ?

This thread quotes mentions 0.3, 0.5 and 0.6" of smokebox vacuum as measured by someone called Jim Ewins.

Also "anyone who has more than 1" of vacuum on a 5"g smokebox has something very wrong somewhere".

They recommend an air-conditioning gauge as being easier to mount than a manometer and using an incense stick to detect leaks.

Dave

I happened to pick up a couple of second-hand books last week that I think answer the questions, well partly anyway..

Air same as steam? Air will be less effective because the water vapour in the steam jet has more mass. For the same reason Mercury was used in high-vacuum pumps.

Continuous "blast" same as intermittent? Dunno if it makes a difference in a scale model but the GWR experimented with a variable blast intended to accommodate varying engine conditions. Not a success apparently, but drivers seem to have made their own adjustments depending on the road and condition of the engine. Here's the example from Tuplin's 1958 "Great Western Steam": "Before we stopped, Bill had turned the blower on, shut the dampers and had gone ahead on the running-board and was opening the smokebox door. When we stopped I turned on the small ejector and screwed the tender hand-brake on. Then while the banker was coming up behind, I went ahead and helped Bill to knock a wedge under the lift-stop of the jumper-top on the blast-pipe so as to get a sharper blast when running hard."

Cheers

Dave

Hi Greg,

County Carlow is quite an interesting design by Don Young circa 1969/1970 in ME.

I will dig out the drawings and check them over for you re the draughting, but Don was very careful with the draughting on his designs. I can also see how County Carlow compares with the Jos Koopmans forumulae for you.

If the loco is built to the drawings I suspect that your main problem is potential gaps around the holes in the bottom of the smokebox for the blastpipe and steam pipes, and leaking piston valves.

There really is no need to resort to monometer readings, especially if you do not have a grasp of smokebox draughting principles. Things have moved on quite a bit in the understanding of these things thanks to Jos Koopmans.

Cheers,

Julian

Thanks for all the suggestions and thoughts. Looks like a water gauge might be the way to go. I checked John Baguley's spreadsheet and it looks like his suggested jet for blast pipe is ab it bigger than mine.

Now a bit of history for my loco. It was built by a local club member who has passed on. He was a very capable builder but I don't think he ever got this loco running properly and I only saw it running a few times in more than 10 years. I believe it's had little running since it was built about 20 years ago.

A person at the club (good builder and good at sorting locos) was looking after the sale and had to do a few little jobs on it to get it running so it was fit to be sold. it had a blown superheater tube. He also change the blast jet to improve the running.

When I got it I ran it a few times and it ran very well. It made more steam than it used and at 60psi running would keep making steam until the safety valve went at 80psi. Then I had troubles running it. In three running days it went from very good to using all the steam from 80psi to 30psi in about 40 metres of track. I initially thought it had blown a super heater tube. I stripped it down and pressure tested it and all was ok.

So put it back together and problem still there. So I have a loco that ran well and in a very short period of time just stopped running. This is why I don't think it would be the valves because I can't see how they could wear out so quickly. I ran it on a rolling road and when the reg is opened there is no gush out the chimney until the wheels start turning.

The pipes inside smoke box are sealed with silcone.

I drew up the smoke box and this is how it looks. The blast jet is 4.2mm. Grey lines are 1:3 and 1:6 as per Greenly's

Edited By Greg H on 23/08/2016 09:40:25

Edited By Greg H on 23/08/2016 09:41:55

Edited By Greg H on 23/08/2016 09:42:59

Obvious I know, but the fact that it was running so well before suggests that ' something' has changed.

You know this too, don't 'change' too many things at once. That leads to disaster !

You've done all the simple things ? De-scale boiler, check the coal, clean tubes, etc ?

It was a good loco , it still is a good loco , you just need to find what has changed.

Yes it does suggest something has changed but I couldn't find a fault.

I haven't descaled the boiler because the water is very clean where I am and so not an issue. Not something required here. I can use my kettle several times a day with tap water for 15 years and it's still just as clean inside as the day I bought it.. I realise that's not so in some parts of the UK. When living in London I first heard of limescale and when I looked in the kettle it freaked me out. I had never seen that before.

Fuel hasn't change. Still working through the same bag. Yes cleaned the tubes a few times now. When it was first lazy I cleaned the tubes. Next run no better perhaps getting worse. Cleaned them again and the next run it was that bad I decided there was an issue that needed sorting.

Yes I just need to find something that's changed but as I couldn't find anything I thought I'd go back to the start and go from there.

I might try that trick with my electric blower on and wave an insense stick around to see if I can see the smoke getting sucked in. If I have teh reg open and loco running if I have the door open it does get sucked closed and so there is some vacuum there.

It might be worth trying to run it on rollers and see if it stays in steam running light.

That would tend to show if the 'leaks' are in the cylinders or valves and not able to operate continuously under load.

Hi Greg,

There is nothing inherently wrong with the dimensions and proportions on your drawing. By altering them you will not get any or much of an improvement. Happy to go into further detail if required. There is also a fundamental problem with applying the Greenly rules per se.

Check that the blastpipe is concentric with the petticoat and chimney.

One run with the lubricator not working or empty can be enough to ruin the solid type piston valves/bobbins on the Don Young designs.

If the valve gear beats are ok we can rule out say an eccentric shifting on the axle or some other valve gear mishap.

The pistons and piston valves can easily be tested under steam or air using the well known fullsize procedure set out on p.95 'Handbook for Railway Steam Locomotive Engineman'.

Look inside the smokebox for evidence of leaking steam joints - the ash and grime will be usually scoured away around any such joints.

I would probably then hydraulically test the boiler and superheaters in one go.

Cheers,

Julian

> The pipes inside smoke box are sealed with silcone.

Run through each of the changes the guy who 'patched it up' applied, recent work is more likely to go suddenly than something that's been OK for 20 years. If he refitted the blast nozzle using silicone it may have developed a leak.

Neil

Way back in the mists of time a USA universtity did drafting (their spelling) on a loco front end using steam from a stationary boiler. They tried both continuous exhaust, and chopped up to make it more like a real loco, and found it didn't make any difference. I must admit this is counter-intuitive, but the measurements don't lie.

Also, check that the holes which let air into the ashpan are not obstructed (shades of Duke of Gloucester)

Covering off comments.

Last week at the club I just ran it on rollers. With only regulator open slightly for normal running speed the pressure went from 80psi to 30psi in 30 seconds or so. It just steadily drops down. Th experience on lookers were baffled because they just couldn't see where the steam was going as it was just coming out the chimney as normal.

The blast pipe is right in the centre of the chimney.

There's plenty of oil getting pumped through and it the runs I've done it's always had oil.

When the steam is up it runs fine on the track and the beat sounds good. It get's the big wheel rock when under load.

Julian thanks for the details on how to test the valves for leaks. I'll test that on the weekend.

As the person that fixed it up had to repair a superheater tube I thought that may have let go. I removed the boiler and superheater and pressure tested the superheater no leak. I tested the boiler with superheater. No leak.

Cleaned it all up and reassembled. The smoke box condition is after 30 minutes of fiddling on the rolling road. It was spotless before that.

So I'm missing something. A check for piston valve leaks will probably be my next thing.

Edited By Greg H on 24/08/2016 11:40:03

Hi Greg,

Have you checked that you blast pipe is concentric with the petticoat pipe and chimney as previously suggested?

It is possible the blast pipe may have got knocked out of alignment during your flue cleaning.

The snifting valve pipe looks to be in an odd position and impinging on the jet of steam exiting from the blast nozzle, and is covered in oil. The oil on the outside of the petticoat pipe front is also odd.

What coal are you using and where is the bag from?

Cheers,

Julian

Edited By julian atkins on 24/08/2016 23:03:28

Is it me , or does that smokebox residue look like the 'soot' that used to accumulate before the ' good ? ' old coal fires I used to know, got going and burned properly ,ie not enough air through the grate ?

Do you hear that characteristic 'roar' from the chimney when the blower only is on and raising steam ?

As I'm sure you know , the coal you use can make an enormous difference to performance.

Hi Julian,

The blast pipe is lined up ok.

The snifting valve is as per the design, but the pipe is not ideal. I’m going to make a right angle fitting so the pipe is horizontal and loops around to the top.

I’m thinking the oil on the blast pipe has come from it running down from the top. I am surprised with the oil on the outside of the petticoat.

Unfortunately coal is not readily available in Tasmania where I live. The coal is also of poor quality. So at my club for about 20 years we have used ‘Briquettes’ which is coal compressed into a brick. They have worked well in locos of all shapes and sizes. The downside is the smoke is a bit hard on the eyes. Recently some members bought some char which they imported from the mainland. The smoke is better, but there is less heat in it compared to the briquettes. The briquettes do no create clinker with just ash. I know it’s not how it’s done in the UK, but has worked well for us.

It is possible the briquettes are not making the heat, but the steam comes up ok on the blower with the loco stationary.

I does use quite a bit of oil, but the oily mess makes me think the blast is not going straight up the chimney.

Edited By Greg H on 25/08/2016 12:17:58

I've read that full size grate design is varied to suit the fuel used, and that not all coal is suitable for use in an locomotive. An loco using the 'wrong' fuel will have trouble maintaining pressure.

Beyond reading about it I'm an ignoramus so please treat this with a pinch of salt.

I'm suspicious of your Briquettes because they are made from Brown Coal, which is the lowest quality coal available. Brown coal is noted for low energy content and it has a high moisture and oily component.

Not all briquettes made from brown coal are equally good. Some are little more than compressed brown coal whilst others are put through a complex process that greatly increases their effectiveness. As you'd expect high-energy briquettes are more expensive than the cheap ones. (Nothing wrong with 'cheap' briquettes used to supplement a wood fire, but not ideal for making steam .)

Is it possible that your club generally uses high-energy briquettes, whilst you've got a bag of the cheaper variety? The way to check would be to run your engine using someone else's briquettes that you know to be good.

Dave