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2"durham and north yorkshire

failure of air test

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David Bothwell 118/01/2019 11:52:41
103 forum posts

Hope that I am in the correct section? I am currently building a 2" Durham and North Yorkshire traction engine, bought part made, got to the stage where I fitted the cylinder to the boiler and after following the designers instructions,i.e. he says block off one of the steam holes, (the one that allows entry of steam or air from the boiler, then attach an airline through an adaptor in place of one of the safety valves, i.e top of cylinder, Did all this, but getting no pressure whatsoever into valves or cylinder, I can only hear air escaping through the exhaust! could someone throw some light on this for most grateful, I can add that a couple of things I did were to place most of the bolts around the cylinder, but took off the valve and buckle

JasonB18/01/2019 11:57:57
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So it sounds like you are feeding air into the regulator chest. First question is does the flow of air you can hear stop and start as the regulator is opened and closed?

Is the blower open or closed as depending on where you blanked off the boiler that may be Live and passing air to the chimney.

Edited By JasonB on 18/01/2019 11:59:54

David Bothwell 118/01/2019 16:00:12
103 forum posts

Hello Jason. The answer to your question is no, Before the cylinder was fixed to the boiler I did apply compressed air to the cavity in the regulator and this moved the piston and altering the valve position it moved in the opposite direction? The blower was opened at first burt I blanked that of as there is no completed chimney

Paul Kemp18/01/2019 20:05:19
240 forum posts
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David,

I am probably being extremely dumb here but what is the test designed to show / prove? If you have removed the valve and buckle then I am assuming you are not expecting it to run?

Paul..

David Bothwell 118/01/2019 20:53:47
103 forum posts

Hello Paul,

I have not removed the slide valve, I removed the regulator (so that air was able to travel straight down to the valve chamber, hope it clears things up. I just wanted to see it run! Before going on to other parts.

JasonB19/01/2019 06:56:33
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Ah so air is free to get to the valve chest.

make sure that the valve is free to find it's own position on the port face, not too loose that it wobbles about but free enough that the air/steam pressure will hold it to the port face. If it is tight it will not seal and air will take the easiest rout which is straight out the exhaust rather than via the cylinder.

Personally for air testing or just playing about with the engine I find it better to use the blow down boss for the air hose and if the engine is not complete than blank off any other holes such as clacks, water gauge etc. That way you can also test the regulator etc.

David Bothwell 119/01/2019 08:11:20
103 forum posts

Thanks for the latest information which I did find quite useful, one question arises,location of blowdown boss.? Do you mean the side of the boiler? (which I was going to try next)

JasonB19/01/2019 09:24:03
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Usually down at the bottom of the Firefox just above the foundation ring. Off to one side or maybe facing forwards on the throatplate.
Paul Kemp19/01/2019 09:48:29
240 forum posts
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David,

As Jason says! I am not very familiar with the DNY engine but there should be at least one bush low down on either the sides or front of the fire box just above the foundation ring for a blow down valve, possibly more than one in which case the others will be for wash out plugs, any of these that are accessible will do to connect your air line if you don't have the blow down valve fitted yet. In fact if you don't have any fittings mounted on the boiler yet then any of the tapped bushes will do for this test as long as you fit blanks to the others. Putting pressure on the boiler as Jason says has the advantage of being able to test the regulator and also the saddle flange to the boiler. You should only need to put 15 or 20 psi on it to get it to turn unless it's exceptionally tight, in which case you need to find out why it's tight and ease it first! Sticking high pressure air on the boiler / assembly may not be the best idea if you haven't checked the integrity of all the plugs and fastenings first with a hydraulic test as even 20 psi of air can project a loose plug out with enough force to do injury if it hits you in the eye! I add the latter because your post suggests you may not have great deal of experience of boilers and steam engines - if that is wrong, my apologies! It's not a massively high risk operation but do take due care and make sure you have a pressure gauge connected somewhere in the system so you know you are not over pressuring the boiler!

Paul.

David Bothwell 119/01/2019 16:43:33
103 forum posts

Hi Paul,

I have just finished trying to get some life into the traction engine, I am at a complete loss as to what is the matter with the traction engine. I have messed about with steam and model engineering for about twenty years or so. The motion is not tight so as you say it should move, but it does not!! I put air (a lot of pressure) to no avail.It is a bot frustrating inasmuch as I have completely removed the cylinder earlier this week and tried air directly down the regulator cavity to see the piston move, it did at either end?

Paul Kemp19/01/2019 20:26:20
240 forum posts
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David,

Mmmm, well......... Like I said I don't have any intimate knowledge of the DNY apart from having seen a few! Never looked at the drawings or made any bits for one! Just thinking it through from general principles though, a few questions;

You said in the first post you could hear air coming from the exhaust. Is this a full volume flow of what you are feeding in or just a wisp?

Did you confirm as Jason suggested that the slide valve (I assume it is a slide and not a piston valve) is free to float on the valve spindle and can find its own seat on the valve face?

Depending on answers depends on where to look next.

Some suggestions though;

Is there a tapping anywhere direct into the valve chest, lubricator input perhaps, where you could put live air direct into the valve chest.and bypass everything between boiler and valve chest?

Are you sure you have the timing right?

Are you sure you have done all the required drillings (silly question perhaps but sometimes it's easy to overlook something).

Paul.

JasonB19/01/2019 20:32:49
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Is the reverse lever in the mid position? you won't get much valve movement if it is, Put it in full fwd or rev and turn the flywheel over by hand and see if you can feel it trying to move by itself or kick back.

A couple of photos of the cylinder and valve gear may help us.

David Bothwell 120/01/2019 09:21:45
103 forum posts

Hi the air was rushing from the exhaust. The slide valve was set equal movement at each end it moves equally. I think I have all the other things mentioned covered, but not 100 per cent sure. I can confirm there is definately NO pressure whatsoever in the cylinder. I have been trying to add images to the post but nothing seems to work, Tried pasting but asks for sequence of button presses including "command" button, google says this is alt?

Paul Kemp20/01/2019 09:45:35
240 forum posts
9 photos

David,

As I said I don't know the internal layout of the DNY but a lot of miniature TE cylinders require a drilling for the exhaust from under the saddle which has to be plugged at the end after. If you have air rushing from the exhaust it sounds like you may not have fitted the plug? This would allow all the air to go direct to exhaust and give the symptom you describe.

Paul.

JasonB20/01/2019 09:49:25
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Paul, it would still need to be getting past the valve to be able to rush out so sounds like the valve is not seating to me.

Posting photos here

I did look at a part built one at the show yesterday, standard practice with drilling up from around liner into the reg chest. Down from reg chest to meet horizontal hole to get steam into valve chest, slide valve with as you say pair of meeting drillings to get exhaust to front of cylinder.

Edited By JasonB on 20/01/2019 09:52:03

Paul Kemp20/01/2019 10:11:10
240 forum posts
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Jason,

Thanks, didn't notice one at the show, trip to specsavers! However OP said he got pressure in the cylinder when he put air direct in through regulator port but when putting air on safety tapping it rushes out exhaust. That implies the valve is sort of doing its job at least? If the lower exhaust drilling blanking plug is missing then pressure in steam space around liner could go direct to exhaust without going anywhere near the valve chest. Either that or a drilling has broken through somewhere it shouldn't?

Paul.

3404620/01/2019 10:34:49
350 forum posts
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May well be on the wrong tack here, so just a thought.

Would it be worthwhile stripping the cylinder of all its bits and checking to see if the bare cylinder is as per drawing ?.

Bill

MichaelR20/01/2019 11:35:57
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Posted by Paul Kemp on 20/01/2019 10:11:10:

Jason,

Thanks, didn't notice one at the show, trip to specsavers! However OP said he got pressure in the cylinder when he put air direct in through regulator port but when putting air on safety tapping it rushes out exhaust. That implies the valve is sort of doing its job at least? If the lower exhaust drilling blanking plug is missing then pressure in steam space around liner could go direct to exhaust without going anywhere near the valve chest. Either that or a drilling has broken through somewhere it shouldn't?

Paul.

Another thought if air pressure is going into the cylinder steam cavity via the annulus, apart from the possibility of a loose or missing exhaust blanking plug, is the blower take off valve open or faulty as it takes it feed from this steam cavity. Mike.

JasonB20/01/2019 11:49:13
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David said it worked when it was off the boiler and he could feel the piston move. So it is unlikely to be lack of or too many holes in the cylinder.

"Before the cylinder was fixed to the boiler I did apply compressed air to the cavity in the regulator and this moved the piston and altering the valve position it moved in the opposite direction?"

To me something has not been assembled right or is stopping the valve from now working

David Bothwell 120/01/2019 16:21:16
103 forum posts

First may I say thankyou to all who have replied to my post, Today I dismantled the cylinder after removing it from the boiler, after a morning and afternoon session on the cylinder, by applying compressed air at the base ( the other hole has been sealed by previous owner) finally got it moving the piston in both directions! So it should work back on the boiler. I also suspect that when I did the adjustments (for equal movement) of the valve buckle I may have helped to "lift" the buckle off the base of the valve chamber. I carefully held it against the base this time, not sure if this was the part of the problem? It was quite a while that I could only get the piston moving one way, but when I "shortened" the length of travel the piston moved. i.e. When it would not move I had it fully extended to the back of the cylinder. If I get it all re-assembled by tomorrow I will do a post. Once again my sincere thanks

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