Broken Sight Glass on an NG16

[Winsley]

I seem to have broken the sight glass on my NG16..... not sure how, but the loco was stationary and just building up pressure prior to running and the driver was suddenly covered in steam and hot water

I've stripped down motion on a loco before (on a Mortimer), but never the 'plumbing' in a cab. Assuming I can obtain a replacement sight glass (from Accucraft?) then I guess it's a case of unscrew the nuts and replace the glass. One question, please, is do I use PTFE tape or just tighten the nuts back up? and are they just hand tight?
Where the water comes out of the boiler into the bottom of the sight glass has some steam seepage when running so I'll replace this washer at the same time (the red one on the photograph ) and hope that solves the problem. In fact, as there is no sight glass holding it, this whole assembly (to the left of the burners) moves from side to side. Does this seem right, or should it be solid?

Any knowledge on this would be much appreciated

 

[Paul M]

There should not be any movement, that is probably what caused the glass to break. I thought that the washers were the seal so no PTFE tape should be needed, but I've seen it being used. Just unscrew the nuts and replace the glass, Accucraft should be able to help you out, but be careful because although the glass can withstand the pressure the water it's still extremely fragile. How old is the loco?

 

[JimmyB]

One question, please, is do I use PTFE tape or just tighten the nuts back up? and are they just hand tight?

As P Paul M has already stated PTFE Tape should not used, unless specified. The unions are parallel threads, and PTFE Tape should NEVER be used to seal these type of unions, it has been know to split unions. Not having details I would imagine that "O" rings on the glass between the nut and fitting, however as Paul has said, it could sealing washers. If you have had this from new then you will know what was in there originally, however if you are not the original owner, you don't know what was previously carried out.

 

[Winsley]

Thanks for your help. I'm the second owner, it's from the first batch Accucraft produced

 

[dunnyrail]

I would be tempted to get a couple of the glasses while you are at it just in case. Tightening should be done with extreme care when refitting the glass. In the meantime you could investigate and possibly fix the movement. Oh and yes check out how tight the screws are on the glasses and which way they turn the record the way they turn for future reference.

 

[Winsley]

Thanks for the good advice

 

[RailsNRivers]

HI, by coincidence have just been refurbishing an old NG16 last few weeks and just changed the glass on mine.

If its any help to you, the key things I found were as follows:

- Found the gasket where the top elbow/banjo goes into the boiler had completely deteriorated (think it making the elbow loose caused the glass to blow). Replaced, new gasket only, no PTFE, etc
- Found the bottom elbow was loose where it joins to the boiler. Needed re-doing, gasket only, no PTFE, etc
- Found the faces of the unions on the elbows were not flat and needed skimming so the gasket sat properly on them without being damaged
- The o-rings in the gauge glass were badly distorted and cut due to the original poor manufacturing of the gauge glass elbows, having nothing for the o-rings to sit on. Carefully skimmed the tops of the elbows flat, o-rings now properly hold the glass when the nuts are done up. O-rings only will seal it properly, no PTFE, etc shoul dbe needed, if it does then something might need fixing on your elbows so the o-rings sit better on them. Only tighten just enough to seal, if the gauge glass has no room to expand when the boiler is heated (because they are clamped too tight) then there is the risk of a glass breakage.
- Critical to make sure the elbows and glass all line up dead-straight when putting them back together otherwise risk of another breakage. Found was best to get the top banjo lined up at dead-on 90deg to the boiler and then use this as the reference to rotate and align the top and bottom elbows.
- Make sure gauge glass is not too long. Enough to generously clear the o-rings but not so much they are butting up against the internals of the elbows, Otherwise again, risk of breakage due to temperature changes.
- Would suggest making a mark on the top banjo bolt so you know when its pointing towards the gauge glass

If you have any other quesitons by all means ask, I have pretty much stripped it and rebuilt it the last few weeks

Cheers

 

[Fred2179G]

I get my 'digest' of threads on a Saturday, so my apologies for not responding for a week!

You may be interested in the Teflon tube option. A couple of experienced steamers here in the USA found that it works as a sight glass.
Sight glass alternative
(I know one of the guys, so if you want some followup, I can provide an email address.)

Secondly, you may have a cap on your top fitting, like this (with Teflon tube!)

The cap (maybe) lets you remove it and push a brass rod down where the glass tube fits into the bottom fitting. With the rod in place, you can tighten the fittings without fear of breaking the glass!
When you have it set and can remove the rod without too much force, you should be able to slide the new glass tube through where the rod went, adding the top and bottom sealing nuts and washers as you go in between the mountings. Then screw them into the top and bottom fittings.

 

[Paul M]

I get my 'digest' of threads on a Saturday, so my apologies for not responding for a week!

You may be interested in the Teflon tube option. A couple of experienced steamers here in the USA found that it works as a sight glass.
Sight glass alternative
(I know one of the guys, so if you want some followup, I can provide an email address.)

Secondly, you may have a cap on your top fitting, like this (with Teflon tube!)

The cap (maybe) lets you remove it and push a brass rod down where the glass tube fits into the bottom fitting. With the rod in place, you can tighten the fittings without fear of breaking the glass!
When you have it set and can remove the rod without too much force, you should be able to slide the new glass tube through where the rod went, adding the top and bottom sealing nuts and washers as you go in between the mountings. Then screw them into the top and bottom fittings.

A very useful tip!

 

[JimmyB]

HI, by coincidence have just been refurbishing an old NG16 last few weeks and just changed the glass on mine.

If its any help to you, the key things I found were as follows:

- Found the gasket where the top elbow/banjo goes into the boiler had completely deteriorated (think it making the elbow loose caused the glass to blow). Replaced, new gasket only, no PTFE, etc
- Found the bottom elbow was loose where it joins to the boiler. Needed re-doing, gasket only, no PTFE, etc
- Found the faces of the unions on the elbows were not flat and needed skimming so the gasket sat properly on them without being damaged
- The o-rings in the gauge glass were badly distorted and cut due to the original poor manufacturing of the gauge glass elbows, having nothing for the o-rings to sit on. Carefully skimmed the tops of the elbows flat, o-rings now properly hold the glass when the nuts are done up. O-rings only will seal it properly, no PTFE, etc shoul dbe needed, if it does then something might need fixing on your elbows so the o-rings sit better on them. Only tighten just enough to seal, if the gauge glass has no room to expand when the boiler is heated (because they are clamped too tight) then there is the risk of a glass breakage.
- Critical to make sure the elbows and glass all line up dead-straight when putting them back together otherwise risk of another breakage. Found was best to get the top banjo lined up at dead-on 90deg to the boiler and then use this as the reference to rotate and align the top and bottom elbows.
- Make sure gauge glass is not too long. Enough to generously clear the o-rings but not so much they are butting up against the internals of the elbows, Otherwise again, risk of breakage due to temperature changes.
- Would suggest making a mark on the top banjo bolt so you know when its pointing towards the gauge glass

If you have any other quesitons by all means ask, I have pretty much stripped it and rebuilt it the last few weeks

Cheers

Nice to hear good practice being used.

 

[Northsider]

All good advice! I replaced the sight glass on my Accucraft Peveril a few years ago and found using a brass bar to align the top and bottom fittings essential, as any misalignment resulted in the glass tube breaking when the glands were tightened. I bought gauge-glass tube from one of the steam suppliers, but the outside diameter wasn't consistent, so I would recommend getting Accucraft ones if possible. New O-rings and gaskets were essential. Finally, the question of how tight to do up the glands: finger-tight, plus a tiny bit of 'nip' seemed about right, then steam test. I broke several replacements trying this...

Good luck!

 

[Winsley]

I’ve ordered a couple of glasses from Accucraft so will definitely take your advice.
Work / holidays permitting, I may have her up & running in the next couple of weeks.
will update when I do

 

[Paul M]

I’ve ordered a couple of glasses from Accucraft so will definitely take your advice.
Work / holidays permitting, I may have her up & running in the next couple of weeks.
will update when I do

Just be careful.

 

[Winsley]

HI, by coincidence have just been refurbishing an old NG16 last few weeks and just changed the glass on mine.

If its any help to you, the key things I found were as follows:

- Found the gasket where the top elbow/banjo goes into the boiler had completely deteriorated (think it making the elbow loose caused the glass to blow). Replaced, new gasket only, no PTFE, etc
- Found the bottom elbow was loose where it joins to the boiler. Needed re-doing, gasket only, no PTFE, etc
- Found the faces of the unions on the elbows were not flat and needed skimming so the gasket sat properly on them without being damaged
- The o-rings in the gauge glass were badly distorted and cut due to the original poor manufacturing of the gauge glass elbows, having nothing for the o-rings to sit on. Carefully skimmed the tops of the elbows flat, o-rings now properly hold the glass when the nuts are done up. O-rings only will seal it properly, no PTFE, etc shoul dbe needed, if it does then something might need fixing on your elbows so the o-rings sit better on them. Only tighten just enough to seal, if the gauge glass has no room to expand when the boiler is heated (because they are clamped too tight) then there is the risk of a glass breakage.
- Critical to make sure the elbows and glass all line up dead-straight when putting them back together otherwise risk of another breakage. Found was best to get the top banjo lined up at dead-on 90deg to the boiler and then use this as the reference to rotate and align the top and bottom elbows.
- Make sure gauge glass is not too long. Enough to generously clear the o-rings but not so much they are butting up against the internals of the elbows, Otherwise again, risk of breakage due to temperature changes.
- Would suggest making a mark on the top banjo bolt so you know when its pointing towards the gauge glass

If you have any other quesitons by all means ask, I have pretty much stripped it and rebuilt it the last few weeks

Cheers

I'm slowly progressing my NG16, your tips have been great . Quick question as I am hopefully near finishing (very slow progress, not enough time!) , should the top elbow have a gasket between the boiler and banjo? And should there be a gasket between the cap on the top elbow? (Where the sight glass slides down).
Accucraft gave me seals and gaskets but none big enough for these two locations and none came off when I took it apart.
Thanks
Pete

 

[Paul M]

I'm slowly progressing my NG16, your tips have been great . Quick question as I am hopefully near finishing (very slow progress, not enough time!) , should the top elbow have a gasket between the boiler and banjo? And should there be a gasket between the cap on the top elbow? (Where the sight glass slides down).
Accucraft gave me seals and gaskets but none big enough for these two locations and none came off when I took it apart.
Thanks
Pete

I would have thought there would be some sort of seal between the joints

 

[Northsider]

I bought some gasket material and made one for the top cap; ideally I'd have used paper punches for this, but I didn't have any...

https://www.amazon.co.uk/Amtech-H1700-Hollow-Punch-6-Piece/dp/B005S0DN1K/ref=asc_df_B005S0DN1K/?tag=googshopuk-21&linkCode=df0&hvadid=208050023643&hvpos=&hvnetw=g&hvrand=13929720776040701358&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9046031&hvtargid=pla-421350505329&psc=1

I didn't remove the elbow from the boiler, so can't help with that, I'm afraid.

 

[JimmyB]

I'm slowly progressing my NG16, your tips have been great . Quick question as I am hopefully near finishing (very slow progress, not enough time!) , should the top elbow have a gasket between the boiler and banjo? And should there be a gasket between the cap on the top elbow? (Where the sight glass slides down).
Accucraft gave me seals and gaskets but none big enough for these two locations and none came off when I took it apart.
Thanks
Pete

Don't know the details of the model, but as an engineer, provide some photos and I can provide some advice.

 

[RailsNRivers]

I'm slowly progressing my NG16, your tips have been great . Quick question as I am hopefully near finishing (very slow progress, not enough time!) , should the top elbow have a gasket between the boiler and banjo? And should there be a gasket between the cap on the top elbow? (Where the sight glass slides down).
Accucraft gave me seals and gaskets but none big enough for these two locations and none came off when I took it apart.
Thanks
Pete

Hi Pete, thanks for the message

There was definitely a red fibre gasket between the boiler and the top banjo. Between the banjo and the cap I can't honeslty remember but put one on anyway.

Mine is all up and running now and has been undergoing some extensive run-in trials and fixes the last few weeks. Did find snags during the first few runs out on track (I think due to more vibrations, etc). This may not apply to the condition of yours (as it may be newer/less used) but I found that the backhead started weeping in a couple of spots. After stripping down again I noticed that most of the threads across the backhead were quite badly deteriorated/eaten away. Possibly de-zincification. I use with distilled water, so possibly either previous owners' water and/or rubbish brass quality used in the original manufacture. Ended up redoing all the threads with graphite compound (as used on full size locos). Has well and truly fixed the problems, she is so sound now and very quiet when steaming, and runs really well now all the steam is going to the cylinders. If you find a similar problem and choose a similar option the graphite stuff is great but be careful you don't get it in the water system when applying it, and make sure its well and truly cured before steaming up, otherwise you could have a self-made grinding paste circulating around your system which may eventually make its way to the cylinders.....

Hope this helps

 

[Winsley]

Thanks for all your help and advice on this one.
It's taken me some time to actually change the sight glass (work gets in the way....)
, but it's now changed and working very well
All your advice was invaluable and much appreciated.
All I need to do now is put back in the R/C and cab....