Loco cylinder temperature

[baggo]

Hi all,

This is probably a tall order but does anyone have a rough idea of the sort of temperatures that a model loco cylinder is going to reach in continuous running conditions

I know from the steam tables that saturated steam at 100PSI is approximately 160 degrees C and probably a bit higher with moderate superheat. I would imagine though that the cylinder temperature will be lower than this due to losses by conduction, radiation etc.

The reason I'm asking is I'm in the process of fitting a piston valve made from the Peek stuff and I've got to try and get the fit right at what will be the working temperature. At the moment I've got the fit slightly on the tight side at 100 degrees C (by boiling the cylinder in water and I'm wondering how much higher to go. I have a digital thermometer which reads to 150 degrees C so I can go that high if necessary by heating the cylinder with a hot air gun or similar.

John

[chris vine]

Hi John,

This is a question I have been meaning to ask the forum as I have had a few problems with expansion on a 7.25 gauge B1 with cast iron cylinders and piston valves.

Initially I made the valve a very good fit but the tended to bind a bit. I had made the assumption that the valve would be a similar temperature to the liners but this is wrong as they are in the direct stream of superheated live steam. The cylinders will be at some mid point between the inlet steam temperature and the exhaust, probably less a bit because of losses.

It was interesting that the rubbing had happened most on the inner ends of the valve bobbins, which I presume were hotter, compared to the outer ends which are more at the exhaust temperature.

In the end I have about 4 thou clearance with sealing being by Clupet rings, with the ring edges doing the timing on the ports.

It will be interesting to see what others think.....

Chris.

[baggo]

Hi Chris,

that's a good point about the valve running hotter than the cylinder and one I'd not considered. I think for the time being I'll aim for a running fit at 150 degrees and wait till I can run it under steam to do any final adjustments. I can see quite a bit of fiddling about ahead!

John