Hi Harry, With a full sized loco, there is usually a copper inner firebox and a steel outer box, these two are held together by steel and copper stays. Also, the firebox tubeplate is usually copper and the tubes rolled into it are steel. Both metals have different rates of expansion as we all know but when an engine is running with the regulator open, a constant temperature is maintained. If the firehole door is opened with the regulator open, there is a great influx of cold air straight onto the tubeplate. This causes the steel to contract quicker than the copper and leads to leaking tubes and stays. If the door is opened when the engine is working, there is a flap on a hinge that should be lifted and this directs the cold air onto the firebed. If you remember that a loco working will generate up to 3000 deg f in the firebox so normal outside air will cool things drastically. I have seen one of our boilersmiths on the SVR, throwing a total paddy because the tubes that had been put in the loco only 2 weeks before were leaking and had been steam tight the day previous. Although it cannot be proven, the only sure cause was running with the firehole door open. Extra unnecessary expense and manpower to re-roll them again. With boilers in 5" and 31/2" gauges, they are silver soldered copper tubeplates, barrels and tubes and whilst there is a slight difference in the expansion rates of silver solder, it is all "glued together" and doesn't suffer the stresses of a riveted steel/ copper boiler. Hope this helps. Dave. ----- Original Message ----- From: "Harry Wade" <hww@xxxxxxxx> To: <modeleng@xxxxxxxxxxxxx> Sent: Friday, June 16, 2006 1:09 PM Subject: [modeleng] Re: Conway At 01:03 PM 6/16/06 +0100, you wrote: >is not good practice to run with the regulator open and the firehole doors >open but does not have the serious results with a copper, silver-soldered >boiler that it does with a steel one. - Dave Dave, What are those results? I've never heard mention of this. Regards, Harry MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line. MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.