britannia smokebox regulator

Back again with (different) smokebox problem, the actuating lever that goes outside the smokebox(that moves the ball valve) in my Britannia does not have enough movement to open and completely)close the valve. Or put another way lever travels a long way without ball moving much! I do not have any measurements for this as I have the three and a half inch engine and guessed dimensions of the parts from photos of Steves 5" build log, so any suggestion would be good, as I have spent more time on this than I think I should have!

Don't know the exact set up, but a few thoughts.

If the cab operating ever travels a long way, but the valve does not, it suggests that there is either backlash in the operating rods,(or levers to spindles ) or they are flexing, and bending,rather than moving.

Alternatively, the lever ratios are wrong and not providing sufficient travel at the actual valve operating lever.

If there is a relay lever part way along the system, with unequal arms, is it connected the right way round, so that it magnifies the cab lever movement, rather than decreasing it?

Howard

Thanks Howard for your thoughts, could be I have the relay lever wrong or one of the other components, as it was guess work throughout . I will checkout the parts you mentioned in the morning, only thing I am sure of is there is no backlash in the rods (they are not flexing) once again thanks for the reply

Another thought: I don't know the locomotive but let's consider the geometric principles.

The ball-valve (if a rotating rather than lift type) needs rotate 90º for full movement, so 45º either side of a defined mid-point that itself gives full mid-points right along the mechanism. So at half port the handle is at mid-quadrant, irrespective of lever ratios.

If that symmetry is not there, the operating-links may become forced into trying to stretch or compress each other as they try to complete the ball arc.

I've an idea these larger BR Standard locos have a prominent reach-rod running along the boiler outside of the cladding, with a reversing-link part-way. In any such mechanism, irrespective of lever ratio or angle of arc, if the rods are parallel that link is ideally square to both rods at their mid-travel.

A similar principle would apply to the valve itself, which if a conventional ball-valve has the ball passage perpendicular to (closed) or in line with (open) the pipe. Usually the handle is parallel to the port, as an indicator; but if the valve is used in some other configuration it (or its replacement lever) may need be at 45º or even some other mid-travel angle, to it.

Good thoughts, Nigel

Howard

I'd suggest checking that the operating rod or rod end doesn't foul the valve lever or valve stem at extremes of travel. If someone made the lever too short (maybe in the interest of exact scale) it may foul the rod or rod end.

Thanks for all the replies, I filed a square on the valve operating lever (as it was unequal when I received it. This is the root of my problem as the lever is placed vertical the ball valve is closed and when operating the lever it needs to move nearly 90 degrees to fully open. i.e. almost horizontal from its original position. I am sure those who built the 5" gauge version (Brittannia) must have got this system working. I can see that I can alter the intermediate link on the boiler (as mine is of equal length) making the lower half smaller i.e. part closer to the smokebox, also increase the length of the operating lever on the ball valve and associated parts

David,

I very much doubt you will need full opening on your ball valve. If you think about most regulators the steam port area exposed when open is not equal to steam pipe bore. Unless the bore of your valve is particularly small I think you will find you will be going like the clappers before it is half open. As long as you get an area equal or just larger than combined port area you should be fine.

Paul.

+1 for what Nigel Graham 2 said about the ideal position for the valve lever being at 45 degrees either side of vertical when fully closed or open.

You may be able to get away with filing a new square with the corners at 45 degrees to existing ones ( I have seen levers that come like this, presumably for just this reason )

If not make a new lever that positions the it at 45 degrees from vertical at each end of the travel.

If you do have to do this, you can make the centre of the hole form the noperating clevis so that the valve opend or closes fully for the travel of the cab lever..

Howard

Thanks to Howard and Paul for the newer posts which I will take into consideration, thanks to all for your help, which I much appreciate!