Saturday 26 July 2014

Over the weekends of the 19th and 26th of July, further work was carried out on the outstanding tasks.

• Removal of the firebox door. Completed
• Finish removal of the welds on the firebox tube plate. Completed
• Removal of the safety valves, crown mounting and clack valves so the mountings can be inspected. Completed, well done Dom.
• Continue clearing the stay tell tale holes. In progress, Chad, Jaydan and Josh were last seen inside the firebox happily drilling.

It must be noted that Greg has been doing a great job cleaning down the exterior surfaces of the boiler, removing the remaining traces of the insulation and other debris left behind from the past twenty years. 

Next week should see the following tasks well under way if not completed.

• Removal of a section of the concrete in the smoke box so the front tube plate can be inspected.
• Removal of the grate so the foundation ring rivets can be inspected.
• Boiler washout to remove the scale left in the barrel as a result of the removal of the small tubes. 

I have been asked over the last couple of Saturdays as to what is the purpose of the stays, why are there holes in the stays and why do the holes only go only so far in, well I'll give it a go to explain;

The sole purpose of the boiler stay is to maintain the distance between the firebox (inner) shell and the exterior shell of the boiler and to support these sheets when the boiler is under pressure.


Arrow points to the stay, the inner firebox and outer wrapper are located to the left and right of the stay respectively

Arrow points to the stay, the inner firebox and outer wrapper are located to the left and right of the stay respectively

 The holes in which the stays are inserted into are threaded of which a long tap is used to ensure that the thread is the same pitch between the outer and inner sheets. The stay itself is threaded however the thread is removed and the material reduced in the area that would be in the water space (white area on the photo above). The holes in each end of the stay also go past the treaded section and just into the area that had been reduced by removing the thread as per the cross section view below.

Stay showing the threaded ends, the 3/16th hole in the end as well as the reduced centre section.

Stay showing the threaded ends as well as the reduced centre section.

Cross section view of the stay.

So why the hole.? The hole or tell tale hole as it is properly referred to has two purposes;
1) To give a weak point in the stay so if it was to break it would more likely break in the area where there is the least amount of resistance i.e. where there is the least amount of material through the section with the hole.
2) To advise the operator that it is broken by allowing water to leak out through the hole.
If the stay was of solid material there would be little evidence that it was broken.

Hopefully the above gives some explanation for the purposes of stays and the reason for the tell tale hole.