Water Levels

I beg to differ, opening of the regulator certainly does pull the water up in the glass. Granted, a degree of this is due to impurities in the water, hence why a loco that is due for a wash out will lift the water in the glass more than a loco just back off wash out, and why R.O. water hardly appears to lift at all.

 

As I said in my post, foaming adds a whole new set of rules to water level shown in the gauge glass, principally due to the density of foaming water being less than that which isn't foaming. The principles of Newton still apply, however, as I've tried to explain in post 18. It needs a much higher head of foaming water to balance non-foaming water and the place where foaming is least likely to take place is at the smokebox end where there is least turbulence.

 

Interesting. I always understood that main reason for the pedestal frame was to ensure correct alignment of the top and bottom gland nuts to avoid stressing and cracking the glasses. As for the perforated backplate, I thought that was primarily to provide a safe(er) exit point for the flash steam etc, and to avoid over-pressuring the protector which might happen if the back were solid?

 

All these are valid points and in my post I did say that it was one reason. I'd say that most gauge glass protector back plates don't have any perforations and, if pressurisation was a problem, it would have more likely been the norm. They aren't exactly close fitting things, though.

All this variation in gauge glass water level and what is going to happen when various events occur, and on different locos, is one of the very good reasons why the knowledge necessary to crew a steam loco is one that cannot really be taught in a classroom and has to include a significant amount of experience.

 

Yes - not disagreeing Steve, just checking my memory and adding to my knowledge

 

I think steve is wrong on the "water lifting in the glass on gradients with the throttle open", and here's why.

Imagine our engine. It's travelling on the level at a constant speed. Our boiler water is (we all agree) level for all practical purposes (lets ignore steam takeoff issues, as they aren't relevant to this question).

Our engine then hits a slight gradient, and travels up it without reducing speed. Now, imagine a 2d force diagram. Forwards and backwards forces remain unchanged - however upward and downward forces have become unbalanced (effectively the track is now pushing the loco upwards, rather than just overcoming gravity).

Think about that in the context of our boiler - the water in it is just being lifted upwards evenly. If you pick your bowl full of water up off the floor evenly, the water doesn't slosh about - it will just sit there.

Incidentally, even if steve was right, the regulator opening would have nothing to do with it - consider the opposite case (coasting downhill with the regulator shut), and think about where the forces are coming from to understand why.

This doesn't mean he's wrong about the observed effect on some engines, it just means the cause of that is something else (probably mostly regulator lift).

 

The water is level, but the boiler isn't; the analogy would be putting the bowl of water on a non-level table. This also demonstrates that what matters is which way the loco is facing, not which way (or if) it is moving, which makes them easy to distinguish in a typical "climb gradient, run round but don't turn loco, descend same gradient" preserved line setup: simple gradient has the same effect in both directions, regulator lift only happens when climbing.

 

But the force isn't being applied by the track and it is also being applied in the direction of motion, i.e. parallel to the track. This you can resolve into two components, one horizontal and one vertical, if you wish, but there is no need. By using your analogy, if you have a train on a gradient and it is stationary, it will never start to run down the gradient because there is no displacing horizontal force, only a vertical one, your so-called track pushing it upwards.

 

Last time I checked gravity only acts vertically. However on a gradient, vertical isn't perpendicular (ie 90 degrees to) the rail (think of walking up/down a steep hill). Therefore the vertical gravity force can be resolved into two directions. One perpendicular to the rail (which keeps the train on the track) and one parallel to the track (which moves the train down the hill).

Stephen

 

i've no problem with that. The tractive force overcoming gravitational pull is parallel with the rail.