What size copper tube?

[springcrocus]

For quite a few of the pipe runs on Britannia the drawing calls for 7/32" dia copper pipe. Now this is as rare as hen's teeth (except for a rather-pricy Reeves offering) and I would like to have an opinion from others.

Should I go up to 1/4" dia or down to 3/16"? The water pipes to the top clacks are fed from the hand pump and the axle pump respectively and the loco will have two injectors feeding the lower clacks on the firebox. Just as important is the look. Will 1/4" dia look too clunky? Or will 3/16" look too weedy?

Your thoughts, Gentlemen, please.

Regards, Steve

[Roger]

You could go up to 6mm, or down to 5mm which are available from Macclesfield Models, that's only 0.5mm up or down.

[stevep]

If you go down to 3/16" for the hand pump and axle pump, it probably won't make too much difference (just a bit more back pressure), but I would say you shouldn't reduce the pipes for the injectors. I believe 'the bigger the better'.

[simplyloco]

Apr 10, 2020 17:36:42 GMT springcrocus said:

For quite a few of the pipe runs on Britannia the drawing calls for 7/32" dia copper pipe. Now this is as rare as hen's teeth (except for a rather-pricy Reeves offering) and I would like to have an opinion from others.

Should I go up to 1/4" dia or down to 3/16"? The water pipes to the top clacks are fed from the hand pump and the axle pump respectively and the loco will have two injectors feeding the lower clacks on the firebox. Just as important is the look. Will 1/4" dia look too clunky? Or will 3/16" look too weedy?

Your thoughts, Gentlemen, please.

Regards, Steve

The celebrated Roy Amsbury used 1/8" pipe throughout his 3 1/2" virtually scale Britannia, and it competed at IMLEC!  My Brit follows his example, so perhaps even 5/32" would be nice in 5" gauge...?

[don9f]

Just for info, the live steam pipes to both injectors on the real thing would be 2” dia, the delivery from the live steam injector to its boiler clack 2.25” dia and the delivery from the exhaust steam injector to its boiler clack 2.5” dia.
These therefore give 0.177”, 0.199” & 0.221” dias. in 5” gauge and if you decide against 7/32”, then 5 & 6mm are certainly good alternatives for the pipes to your clacks on the barrel. I’m sure the 3/16” would work but would look a bit small in my opinion.

Cheers Don

[jma1009]

Steve's injector pipework should be determined by the size of the injectors he is going to fit; and we don't yet have details of these. I've never seen 7/32" dia thinwall pipe specified for injectors previously, and do not recall it listed in my old catalogues, so a peculiarity of Jim Perrier?

Axlepumps and handpumps are a bit more forgiving, and can deal with smaller bore pipework; the obvious thing being the bore and having no sharp bends or restrictions same as would apply to the injector pipework.

Don't use thick wall car copper brake pipe!

I would second Macc Models Ltd, though I have always used the K&S range though this is no longer being made. Maidstone did a good supply of thinwall copper pipe from what I gathered from others, and are worth a try as well.

I have used odd sized/non-standard pipework on injectors out of expediency, but we really need to know what size injectors Steve plans to fit to his 5"g Brit, and of which make.

Cheers,

Julian

[springcrocus]

Apr 10, 2020 20:12:47 GMT jma1009 said:

Steve's injector pipework should be determined by the size of the injectors he is going to fit; and we don't yet have details of these. I've never seen 7/32" dia thinwall pipe specified for injectors previously, and do not recall it listed in my old catalogues, so a peculiarity of Jim Perrier?

Axlepumps and handpumps are a bit more forgiving, and can deal with smaller bore pipework; the obvious thing being the bore and having no sharp bends or restrictions same as would apply to the injector pipework.

Don't use thick wall car copper brake pipe!

I would second Macc Models Ltd, though I have always used the K&S range though this is no longer being made. Maidstone did a good supply of thinwall copper pipe from what I gathered from others, and are worth a try as well.

I have used odd sized/non-standard pipework on injectors out of expediency, but we really need to know what size injectors Steve plans to fit to his 5"g Brit, and of which make.

Cheers,

Julian

It's not the injectors I'm concerned about, those are beneath the cab floor and are out of sight. I's the pipes feeding the top clacks I'm most concerned about.

Thanks for the info about the car brake pipe. I may well have fallen into the trap of thinking that thinwall pipe would be inadequate.

Based on Don's info, 5mm (thanks, Roger) may be the way forward but further thoughts from members would be welcome.

John, I think 5/32" would definitely look a bit small.

Steve, the drawing shows 3/16" for the pipes feeding the real injectors but I may lift that to 5mm if I get that for the other pipework.

Regards to all, Steve

[jma1009]

Hi Steve,

The OD is obviously important for nipples and Union nuts etc, but really it is the bore that is important and SWG.

So, by way of comparison, I have quite a lot of very thin wall copper tube of odd 9/64th OD, and will be used on Stepney. I always make my own nipples and union nuts anyway. This pipework came off 'Linda' when I standardised 'Linda's pipework from the manifold to the injectors (Steam to injectors) to thin wall 5/32" pipe off the K&S range.

It is the bore and run of the pipes that are important. You will probably need a few reverse bends etc to get rid of the 'hammering' in the pipe from the axle pump - or just delete the axle pump if you have 2 injectors!

Feed low down on the backhead always causes problems with scale/solids mucking up the check valves, that injectors do not like, as a slight weep on the check valve means the injector heats up, and may not 'pick up' on starting. Personally, I would save the 2 top feeds for the 2 injectors.

Cheers,

Julian

[steamer5]

Hi Julian,
On your comment on “ hammering” in pipework from axel pumps,do you know of any full size locos that had pulsation dampners fitted to help reduce / eliminate the hammering? Just a curiosity question. Several of the pumps at work have them, they can be maintainence intensive!


Cheers Kerrin

[uuu]

Ken Swan's "Wren" design had an air bottle on the crosshead pump - I suppose the prototype had this also, as it's quite prominent.

Wilf

[jma1009]

Hi Kerrin,

Yes, all the LBSCR locos of Stroudley vintage had the sort of dampener described by Wilf, and I have the drawings if required.

I've seen quite a few miniature locos have 'hammering' in the pipework from axle pumps, including daresay my own first loco!

Cheers,

Julian

[steamer5]

Hi Wilf & Julian,
Thanks for the info, can’t say I’ve see any loco down this end of the world with them, hence my question.

The pumps at work have a rubber....not standard rubber...open one end bladder contained in a vessel, these are then Nitrogen charged dependent on system pressure this can be anything up to 500 bar! One set of pumps has 1 m3 vessels on both suction & discharge with no bladder so different ideas from different makers.

Water and or steam hammer can do some serious damage! I’ve seen large steam lines jump & bend supports & brake concrete!

Cheers Kerrin

[mbrown]

Quite a few Kerr Stuart locos - narrow gauge ones anyway - had an axle driven pump with an eccentric almost exactly like many models. On the ones for which I have drawings, like the early Gwalior Railway 4-6-0s, the pump has what looks like an air chamber on the delivery side, presumably to iron out the flow, and a pet cock just under the clack which would allow any air in the system to be voided. As the pump was regulated by cutting back the inlet rather than by having a by-pass arrangements, I imagine it was quite prone to air getting into the system which would have caused all manner of bangs and crashes…. The Corris Railway's No.4 from Kerr Stuart (now the Talyllyn"s Edward Thomas) was built with exactly that sort of pump and the keyway on the axle for the eccentric, and the mounting hole in the frame stay, are still visible. As some point, the pump jammed and bent the stay slightly leading to the removal of the pump altogether. Maybe that was caused by an air lock, I don't know

Malcolm