BOXHILL by Martin Evans

[jma1009]

i should perhaps state quite clearly that Stepney will be the first loco ive fitted with radiant superheaters as opposed to my usual construction of rather thin gauge copper super heater elements of return bend type with the return bends being very slender and thin also, ending just short of the tubeplate.

the superheated steam is going along the superheater elements at quite a rate of knots. it is unlikely to lose temperature in the fraction of the time it takes to get to the steam chest/s, especially as the flue gas around it is always above this temperature, even if heat transfer in the front 2/3rds of the superheater flue is marginal. what is important in any superheated loco is that when expanded in the cylinder the steam shouldnt start to condense. this makes a lot of difference to how a loco behaves and can be 'notched up'. in miniature, less fuel consumption and less water consumption are rather nice benefits (and makes driving so much more pleasurable), plus as i wear glasses not getting your glasses steamed up especially in a tunnel is another favourable benefit especially when sighting signals!

cheers,
julian

[Roger]

I'll be interested to hear how they perform, I reckon that's a really efficient design. Interesting though the discussions about concentric ones are, the case for them in smaller sizes is not very convincing in my opinion when you look at how neat and simple yours are.

[jma1009]

for anyone who might be interested here's my drawing for the captive blowdown valves illustrated earlier for 5"g terriers.

the original valves are neither captive plus when opened interfere with the coupling rods. not a nice thing to happen!

cheers,
julian

[Roger]

Very useful thanks Julian, squirrelled away for future reference!

[jma1009]

edited!

[jma1009]

here's the pic of the completed valves back on 31st august this year

cheers,
julian

[Roger]

Thanks Julian, that's very useful. A very neat valve indeed.

[Deleted]

Hi all!
I found this little gem on YouTube, not the greatest of videos but it illustrates something very clearly which Stepney will never ever have again and possibly neither will Fenchurch depending on how bad Fenchurchs cylinder block is deemed to be.
It is of course the characteristic "hoo haa" noise the exhaust makes, very noticeable on Stepney but not so much on Fenchurch.
So my conundrum is, why do terriers make this noise?? (George, not a word! )
Sort of a thread hijack but a topical one! Sorry Julian
youtu.be/P8h3STOY02I

[Roger]

My guess is that the it's because the chimney length happens to be tuned to a frequency that closely matches the pitch made by the exhaust blast.

[Deleted]

Nope, that would create the same tone rather than alternating tones (would that even be possible?!)

[Deleted]

no idea myself but loved the video...great little engines....

[cplmickey]

Well although I've no idea why it might happen it seems to suggest unequal exhaust passage lengths, or possibly unequal passage diameters?

[jma1009]

i am more familiar with terriers W8 Freshwater and W11 Newport on the isle of wight at havenstreet, and both have similar (but not identical) characteristics so far as the sound of the exhaust is concerned.

as to exactly why the terriers have a distinctive exhaust sound im not sure! i think its a combination of a tall chimney (in fullsize the base of the chimney forms the petticoat pipe and flare), a very good valve gear, and very well designed cylinders. also because the base of the chimney forms the petticoat pipe the exhaust pipes and blast pipe are very tall. other locos have some of these characteristics but perhaps not all together.

[Deleted]

Nope, the clue was the comment about the cylinder block.....
cplmickey is closest so far but not unequal passages or passage diameters.
This is fun!

[jma1009]

hi ben,
the blocked off connection on the cylinder block to the condensing apparatus?
cheers,
julian

[uuu]

Concentric blast pipes?

Wilf

[Deleted]

Bingo!!! Julian has got it! Where the two cast in takeoffs for the condensing gear on the block were blanked off, they effectively act as crude whistles, the difference in tone due to slight differences in the lengths of those. The difference in volume between 55 and 672 (and all the other terriers too) must have something to do with the bore of the cylinder and therefore the volume and speed of the steam passing over the capped tube (regulator setting affects the noise too)
That's why 55 will never sound the same again, the new blocks don't have or need the condenser takeoffs cast in

Well done all, some interesting ideas!

Cheers
Ben

[jma1009]

thanks ben!
im afraid that my version of Stepney wont sound like a martin evans terrier either! the exhaust passageways are much bigger right up to the blast nozzle, and when tested on air after the valves were set last year had a very distinctive clear GWR 'chonky' sound! ive also redesigned the smokebox innards more to my way of thinking for such things and i would be surprised if the blastpipe nozzle cant be opened up by quite a large amount. incidentally the original smokebox arrangement doesnt follow the Greenly 3:1 rule, martin evans setting the petticoat pipe choke too low/the blast nozzle too high by a considerable amount!
cheers,
julian

[Deleted]

Hi Julian--------- could you just expand on that Greenly 3:1 rule please ??....... EDIT}--- I've just put that into Google and found this very knowledgeable chap over on the ME Forum}----------- www.model-engineer.co.uk/forums/postings.asp?th=76967

[ejparrott]

Reminds me, really must run the 1:6/1:3 figures over my engine....

I believe it equates to 19 and 38 degrees?