Boiler Water level

[John Morgan 1Participant @johnmorgan1]

I’ve just run my Modelworks 5″ Britannia for the first time under load, up to now I’ve been practicing on a rolling road. I only managed 1 1/2 miles before winter arrived but enough to notice that with the regulator open and on the move, the water level rises to the top of the sight glass indicating boiler full to overfull. Closing the regulator the water level falls to the bottom, indicating action required!

Only one Blow Down Valve was supplied and fitted to the bottom of the glass. Opening/closing does not change the readings.

How should I use the information? The obvious answer is to use the lower reading but I do not want to risk running water into the cylinders with the steam when the regulator is open.

Is this a known phenomenon or do I need to make adjustments?

Thanks. John

[SillyOldDufferModerator @sillyoldduffer]

This is Armchair advice, and I hope an experienced loco builder will comment.  My interest is in full-size boiler accidents rather than model steam and misleading water gauges are a common factor.   They can read high when the boiler is dry and about to melt, or low when it’s full to overflowing.

I believe something is wrong, and the Britannia’s gauge can’t be trusted. Needs to be fixed – expensive bad news if water doesn’t completely cover the top of the firebox.  Even if it doesn’t puncture, likely to be permanently weakened by severe overheating.

In theory there is very little to go wrong with a water gauge.  The lower pipe connects into the boiler below the water-line, and the upper pipe connects to the steam space.  As the pressure on both sides is equal, the water line in the glass is level with that in the boiler.    What could possibly go wrong?

In practice a great deal!  The gauge relies on steam and water pressure being equal on both sides of the glass, and it might not be.

• Valves not fully open.  (The ones used to disconnect the gauge if the glass breaks.  Some nasty accidents due to fitters putting handles on the wrong way round, leaving dirt in the valve, and driver error.)
• A part blockage on one side of the feed pipework, so pressure can’t equalise in the glass.   A gauge reading high when the regulator is open suggests the steam-side pipe is blocked.  Could be scale, dirt, or – in a new engine – flux, or excess solder in a joint.  Or the pipe diameter is just too small.
• Design is another potential issue.  The steam side should have it’s own private connection into the boiler.  In practice, many designers or builders, connect the gauge to another convenient external steam pipe, perhaps going to the whistle, injector, water pump or whatever.  It simplifies the build.  The problem is the water gauge then responds pressure in the external pipework, not the boiler pressure, and it could be much lower.  The pipes are colder than the boiler and whatever it is feeding could be leaking. External pipe pressure can drop much lower than boiler pressure, causing the water gauge to give a false level.

All three faults tend to show up when the engine is consuming steam.   Working hard causes the boiler pressure to drop and pull steam out of the whole system, causing pressure in external pipework to drop significantly.  Then gauges that seem OK at rest, go wrong when the engine is ruining.

Check valves, look for blockages throughout, and make sure the gauge feed pipes are of the correct diameter.  If the gauge pipe connects to external pipework or a manifold as per design, check whatever else is connected for leaks or empty space remote from the boiler.  If the build was simplified by ignoring the design and connecting to an external pipe instead of making a separate connection, rebuild in accordance with the design.

Dave

[Nigel Graham 2Participant @nigelgraham2]

An odd one, that behaviour. It should not happen on any steam-engine.

My first thought was simply from not using the bypass-valve on the feed-pump (if one is fitted); but that would obviously leave the boiler full when stopped. That’s not the case, you say.

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The water rises and falls in the glass – so the fitting’s passages are clear. So too, we hope, the firebox water walls, which can eventually choke if the feed water is hard. An unchanging water level is an ominous sign!

The change you see does not seem the surging we might expect in a locomotive under way, as the water sloshes back and forth, especially in a long boiler. The level will wobble up and down a bit but should be fairly well settled at steady speed on a good track, and of course stationary.

However, you describe the glass responding to the regulator being opened and closed.

That makes me ask:

1) Is this only when accelerating or decelerating (though it would have be rather brisk to make much difference) or when the locomotive is pulling at a steady speed as well?

2) Especially if the latter case, where are the steam take-off point and the gauge-glass top fitting, with respect to each other?

 

I don’t know the Modelworks ‘Britannia’ design and I am not sure of the full-size layout, but the main steam outlet should be high in the dome, whether the regulator is also there or in the smoke-box. Whereas the connections to the gauge-glass are normally on the backhead, and the other fittings take steam from a manifold above that. So all too far apart, in proportion to the boiler’s overall size, to affect each other.

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(You might ask, why not also put the gauge-glass top-fitting on the manifold. It’s not good practice because the flow of steam through valves to other fittings may, in theory at least, create sufficient depression in the gauge-glass connection to draw the water up in the glass, giving a false reading. How real the effect is, I would not care to say and it would be specific to the boiler and its operation anyway, but it is Something Not Done!)

 

[Brian Baker 2Participant @brianbaker2]

John, greetings, the water gauges valves on the 71/4 gauge Modelworks water gauges are sealed with PTFE seals, and the drillings through the valves are quite small diameter.  What happens is that when warm the PTFE creeps, and can block these small holes, which causes effects such as you describe.

I am not sure if the 5 in gauge water gauges are the same, but I would not be surprised, so I suggest you have a look.

 

Regards

Brian B

[duncan webster 1Participant @duncanwebster1]

There was some correspondence a few years ago suggesting that even if working as intended, the bottom gauge glass fitting on Winson Britannia boilers was too low, so that with water showing the firebox crown was not covered. Chap in our club confirmed this on his. Whether Modelworks (who took over Winson) corrected this I don’t know. Easily sorted, just put a bit of tube over the glass to blank off visibility of the bottom end.

Strangely I don’t think there were any reported failures.

[noel shelleyParticipant @noelshelley55608]

Before something nasty happens you MUST resolve this issue ! High when opening the regulator and low when closing sounds like surging ! if you have only done 1.5 miles then you lack experience. You do not make it clear as to if this applies when on a rolling road – if not then surging ! Something you will learn to live with !   If not surging then, Others have commented on pipe work and different pressures under working conditions. The construction of the gauge glass fittings should allow you to remove the glass, then remove the fittings to check that all the portways are clear and look for packings, be they O rings or other types that have somehow closed over the tube end. When reassembling use steel rod to align the fittings true before refitting the glass. Good Luck Noel.

[John Morgan 1Participant @johnmorgan1]

Thank you all for your replies.

Running on my rolling road; I did not notice the change in water level when operating the regulator. Could be that I was too busy learning and checking the fire and injectors and lubrication or just that with no load and the regulator being only just “cracked” open, any change could have been minimal.

Accelerating or decelerating; If memory is correct(!), there was a lot going on during my first run, the water level in the glass instantly changed as I opened and closed the regulator. I first noticed this after just rolling along slowly, on the level, then accelerating away. Unfortunately I did not notice how just running at a steady speed affected the water level. It was a cold, wet day and I was having difficulty seeing the road ahead through the steam, which may be another problem I’ll have to address. That is why I slowed down, to change my gaze to checking the loco levels.

My feeling is now that the lower reading is the one to use for operating the injectors. I will check for blockages in the pipework, seals and valves and hope that this is the reason.

Here is a link to a Modelworks Britannia kit, not mine, which shows their fitting which should confirm that it is a conventional design, no shortcuts! I’m not sure how else to display the pictures, so apologies to its owner John Johnston.

https://britanniabuilder.com/kit18pressuregauge.jpg

https://britanniabuilder.com/Kit18cwatergauges.jpg

Steam outlet; The collector is not up in the dome, the done is a dummy and the collector pipe runs uphill from the smokebox, 10mm (max) below the top of the boiler. Eyeing it up, it is just above the top water glass fitting. With hindsight I should have modified the end, turned it up into what dome there is. Another picture from John J which shows the small space in the dome I could have used

https://britanniabuilder.com/Kit17contents2.jpg

 

I will be back on a rolling road ASAP and make better notes, using your helpful comments to guide me.

Seasons greetings,

John

[norm nortonParticipant @normnorton75434]

Hello John

I think you have now made it clear that the rise and fall of water level is seen when you are driving on a section of track – as you accelerate and decelerate this is quite normal. We normally note the water level when at a steady speed. Similarly, you will see the water level rise and fall when going up and down hill. The Britannia has a long boiler and levels change quite visibly.

If you have an early 5″ gauge Winson you will need to check the firebox height with reference to the bottom of the gauge glass as suggested. If however it is a later Modelworks boiler as you say then this height error was corrected.

You must ensure that you can blow down both the glasses to visually ensure the passageways are clear, and this will be a part of the steam test.

Norm

[noel shelleyParticipant @noelshelley55608]

Seasons greetings John, Your description and the pictures make things much clearer. With a long boiler and quite short gauge glasses surging and management of the boiler may prove challenging but something practice will master ! The glasses going straight into the boiler more or less rule out other factors and the rapid fluctuation would seem to indicate the portways are clear, correctly showing the water level. For peace of mind I would run it on the rolling road and pay special note to the operation of the gauges whilst operating injectors or feed pumps and see that level changes are correct. If you are a member of a club seek the advice of the boiler inspector. Good Luck Noel.

[John RutzenParticipant @johnrutzen76569]

I would agree, having looked at the pictures.  The length of actual glass is very short and you would expect to see that much variation due to the uneveness of the track and surging.  Is there any way you could make new gauge top fittings to increase the length of the glass?  I would like to see double that length of actual tube.

[Paul LousickParticipant @paullousick59116]

My first thought was that the steam take-off for the engine was affecting the water column, which is why it should be independent of the column but your photos show this is not the problem, so probably surging as you accelerate and the water runs to the back of the boiler.

Does the water settle to the correct level an a long stretch of track after you have obtained top speed ?

This is a bigger problem on a traction engine because roads are not as flat and much steeper than train tracks. You have to constantly monitor the eater level and anticipate any change in level of the road.

Going up a big hill, the water in the glass may be all of the way to the top of the glass, then when reaching the top of the hill and leveling off you have to ensure that there is enough water in the boiler to cover the crown. Alternatively when going down a hill the water in the glass my disappear but you have to have water covering the crown but not too much that you will prime the engine.

Some of our traction engines have brakes and we shut off the steam when going down a hill and rely on them to slow the engine but those without brakes have to use the reverser for stopping and water level is much more critical.

On a very steep hill the only way to go down it, not let it prime and keep the crown covered is to go down in reverse. Also good practice to go down a hill in the same gear that you need to go up it to ensure you have enough stopping power.

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