Here is a list of all the postings John Baguley has made in our forums. Click on a thread name to jump to the thread.
|Thread: Boiler Test Codes|
The subject of fittings does seem to be a grey area. Appendix B of the code says:
"In addition to the normal inspection for leaks, adequate joints, correct thickness of materials and the absence of any appreciable distortion/bulging to any surfaces, inspectors may wish to consider the following points: "
Note it says may wish to, not shall or should !
The criteria in appendix B for fiitings seems to be the same for new and previously tested boilers i.e.
'All screw operated valves should be checked to ensure that they cannot be screwed out whilst under pressure'
My interpretation of that is that a boiler with valve spindles that can be unscrewed should be failed whether it is new or old but the opening paragraph to appendix B suggests that the inspector can choose to ignore this?
Definitely something that needs to be clarified!
Edited By John Baguley on 14/09/2009 00:42:40
A few details and pictures here:
the 'cauliflowers' were the nickname of the 0-6-0 express goods engines designed by F W Webb for the London and North Western Railway. Their official title was '18 inch Goods' I think but were also known as the 'Crested Goods' The nickname came from the crest on the wheel splasher which resembled a cauliflower from a distance!
Edited By John Baguley on 07/09/2009 20:39:10
|Thread: Balancing the steam pressure on the slide valve|
I'm presently working on an 0-6-2 tank loco based on Simplex castings and my intention is to fit balanced slide valves to reduce the load on the valve gear.
The principle behind balancing the valve is to isolate part of the upper surface of the valve from the steam pressure in the steam chest so reducing the force pressing the valve onto the port face. If you do a search for balanced slide valve on the net you'll find some info which may be useful.
There are various ways by which this can be done in 'our' sizes but will probably require the valve design altering and also changing the drive from the slot and nut to a buckle type drive on the outside of the valve.
One simple way is to turn a short spigot on top of the valve which holds an O ring between the top of the valve and the underside of the steam chest cover. This seals the area inside the O ring from the steam chest pressure. I am not sure how long the O ring will last used like this as they are not really designed to slide. The underside of the steam chest cover would need to have a very smooth finish. This method has been used though and described in Model Engineer a couple of times.
Another way is to fit a 'balance' piston into a bore in the top of the valve which presses and seals against the steam chest cover, again isolating the part of the valve containing the piston. Another version of this has the balance piston mounted in the steam chest cover and the piston has a flat plate that presses on the top of the valve. If you have already made the valve, this option might be possible as the plate could press on the four corners of the valve left after machining the slots for the drive nut and the valve spindle?
Both of the above methods need a small 'vent' hole so that any steam that does get past the O ring or balance piston is vented to atmosphere or exhaust otherwise the pressure will build up on the top of the valve and render the balancing ineffective.
I've done a bit of research through articles in Model Engineer etc. and it seems to be the practice to make the area of the balance piston (or O ring) about 0.9 times the area of the exhaust cavity in the valve.
I'm just designing my set up at the moment but haven't finalised my ideas yet so I can't say for definite how I will do mine. However, I do intend to have the exhaust exiting through the top of the valve and a balance piston and then through the top of the steam chest cover. (This is the method Don Young used for his 5" gauge Hunslet). This gives a freer exhaust as the steam does not have to exit via the usual tortuous route through the exhaust port in the port face. If you like, I'll post some more details when I've finally sorted the design.
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