Question about stay bolts?

I have question on stay bolts. I know what the stay bolts are for on the firebox but what are the bolts all around the boiler near the cab and firbox for? Are these also stay bolts? Are all these bolts on the boiler near the cab and fire box to help the boiler with the mass amount of pressure? Heres a photo to help explain, look near the cab and you will see all the bolts im talking about on the boiler.
http://www.flickr.com/photos/7552532@N0 ... otostream/
I hope this helps. I was asked today what those were for and i couldnt give a clear answer, so i figure i would come to the experts Thanks for your time.

any flat sheet subject to boiler pressure on one side and atmospheric pressure on the other must be supported by bolts or stays, the pattern depenading on the pressure, the strength and thickness of the steel plates. the boiler shell wrapper sheet around the firebox and inner firebox are both made up of flat sheets, with a water space between them.

given a boiler pressure of 100 lb pressure per square inch, picture a flat sheet with an area of 10 inches by 10 inches - 100 square inches times 100 psi gives a load of 10,000 lb force on that small area. a single stay of 50,000lb tensile strength with a cross section area of 1 square inch would be addequate to support this area with a factor of safety of 5. thus a pattern of stays or stay bolts must be provided, with an interval in the neighborhood of every 5-10 inches, to prevent extensive flat sheets from bulging or buckling under pressure.

actually, the inner sheet subject to pressure on its "outside" and subject to the radiant heat of the fire on it's "inside" is more vulnerable than the exterior wrapper sheet, so the stay pattern is dictated by the calculated stress in that surface.

a "stay" is welded into the sheet it supports, a "stay bolt" is attached by threading, or by bushings.

Rail Gun,
I looked at your photograph and what you're describing are called flexible stay bolts. The other ones below are called rigid staybolts. The flexible stays are usually located near the edges of the firebox where you have the most movement due to expansion. The top of these flexible stays has a cap that is threaded on to a sleeve. Under the cap the top of the stay is ball shaped to allow movement. I would recommend finding copies of old ICS courses that have several volumns about steam locomotives and old locomotive cyclopedias that describe this stuff in detail. They also show details of how the boiler courses are riveted together.
Leverett Fernald

I'd also highly recommend you find a copy on DVD or VHS of the program "Running A Steam Locomotive," wherein Monticello & Sangamon Valley travelling engineer Charlie Daigh, who is no longer with us, takes you through the design, construction and operation of steam locomotives using the museum's locomotive No. 1. It's fascinating as a primer and fun to watch and re-watch even today. The best part is when he's being videotaped INSIDE the firebox rolling flues by hand.

Last I knew, this was being offered as Volume 1 of a three-volume set; later volumes move on to bigger engines. But you'll really want Volume 1.

-Will Davis

Thank you all for your help and detailed answers, im going to go get these dvd's that yall suggest because it is certainly hard to pick up a book and trying to read about parts and how they work on a steam engine when your brand new to the world of rail roading and steam engines. I will most certainly get these dvd's and watch them, so next time i research and read about them i will have a better idea of what im looking at and researching. Thanks for all the help!

Typewriters wrote:I'd also highly recommend you find a copy on DVD or VHS of the program "Running A Steam Locomotive," wherein Monticello & Sangamon Valley travelling engineer Charlie Daigh, who is no longer with us, takes you through the design, construction and operation of steam locomotives using the museum's locomotive No. 1. It's fascinating as a primer and fun to watch and re-watch even today. The best part is when he's being videotaped INSIDE the firebox rolling flues by hand.

Last I knew, this was being offered as Volume 1 of a three-volume set; later volumes move on to bigger engines. But you'll really want Volume 1.

-Will Davis

Excellent video. I've watched it a dozen times or more, and we used it in training of our new - and seasoned - firemen and engineers at NJMT. www.njmt.org

To add to this: Many stay bolts are drilled with a hole through their length. Reason? If the stay breaks, steam and vapor will escape from the hole leting you know it needs to be replaced. If a lot of drilled stays are leaking in the same area, that shows possible boiler plate damage and warping.

Threaded staybolt removable and replacement is a long and tedious job. Even more fun when you have to take other things off that are in the way to get to them.