Superheaters for model loco

[Barneydog]

Hi Guys,
Superheaters on model locomotives are generally made from welded stainless steel tube. Do they have to be welded? Can they be silver soldered? Can they be made from copper tube instead? I have seen some made from copper so it must be possible. If the issue is that they do not last as long as copper then I will make spares and make them easily replaceable.

Regards

Julian

[pgp001]

I was looking at a friends model radiant superheater last night, I dont personally know a lot about them, but he had made it from stainless steel and silver soldered it together with no problems.

Phil

[Jo]

You can buy pre welded stainless U bends for super heaters from a number of suppliers. It is the right sort of stainless tube & weld. I think when I looked into making my own stainless elements the stainless tube was half the price of buying the ready made elements.. It is not very easy to get that nice curve/spike with good steam flow just right for silver soldering and you end up adding a big joining block if you get it wrong. Is it worth the hassle?

Yes you can use copper super heaters - They tend to sag in the firebox due to the heat softening them. This is solved by making them shorter = less super heating effect or by supporting them by some sort of bracket = modifications to the boiler. They also tend to have one of those joining blocks that  levels your coal off for you dumping it at the back of the box as you try to shovel it in

Jo

[steamer]

Also.....go easy on the amount of superheat.   It complicates internal lubrication significantly.

100F is great.....keeps things dry in the cylinder without cooking the lube and loosing all condensation.  That condensation is the best cylinder lubricant.

Dave

[Steamer5]

Hi Julian,
 For what it's worth my loco had copper superheaters from new, the lasted up until about 10 years ago. I had owned the loco for about 15 years prior to that so I guess they were likely to be another 15 or 20 on top of that, the loco has had a reasonable amount of use over the years, although the guy I brought it from hadn't used it for several years prior . They didn't or tube into the fire box. First indication that they were stuffed was LOTs of steam coming up the spout when opening the regulator! End of running that day.
On removal it appeared that one had been eroded away. I've replaced them with stainless & then now go over the fire.
 So copper could last you quite awhile, or you pay your bucks & put in stainless! The fire box end is a stainless block as small as possible & welded, had a work mate who could TIG weld them, smoke box end silver soldered to the header fitting.
Read on another site the other day were a gent had threaded & used sealant on the block end, sounded like a  neat idea. He reckoned that he had had good service out of it so that's another choice.

Cheers Kerrin

[Barneydog]

I will use stainless if I find some going cheap which I can silver solder or give weld. If needs be I will make a copper one for the interim. I am looking at using two displacement lubricators, one per cylinder rather than a mechanical one. If the superheater dries the steam will displacements still work properly. It is the water in wet steam that displaces the steam oil so will they still lubricate enough. My simplex is designed to have a superheater so I will fit one.

Julian

[Steamer5]

Hi Julian,
 Looks like you have a plan....& a cunning one at that!
On the superheated steam front, and at the risk of getting flamed......in our loco's its doubtfull that we actually get any superheat, or if we do very little! Ok the reason.....you can't superheat wet steam.....in industry boiler makers go to great lengths to REMOVE any intrained water as the steam exits the boiler via cyclone separators prior to the steam going to the superheaters.
In our size we tend not to have any form of water separator or if there is it's pretty crude. Our superheaters more than likely just tend to dry the steam & in doing so increase the volume available & hence we can run notched up & do get the benefit over non superheated fitted loco's.
Now this isn't based on any hard testing but on long discussion over a number of years talking to other loco nuts & working with boilers in the full size petrochemical industry

Right dones his helmet & drives under a rock!

Cheers Kerrin

[steamer]

I will use stainless if I find some going cheap which I can silver solder or give weld. If needs be I will make a copper one for the interim. I am looking at using two displacement lubricators, one per cylinder rather than a mechanical one. If the superheater dries the steam will displacements still work properly. It is the water in wet steam that displaces the steam oil so will they still lubricate enough. My simplex is designed to have a superheater so I will fit one.

Julian

Not with Cast Iron cylinders.    With CI cylinders and Saturated steam...very little internal lubrication is required.  The condensate is the lubricant.     As soon as you superheat though.  YOU WILL need internal lubrication, and it has to be an oil that will stand the heat as well.  Not so much of a problem with a locomotive...other than eating the lube oil coming out of the stack, but on board a steam boat, the last thing you want is oil in the boiler feed water (running condensing).

On Sabino, the 75 HP Paine ran 14-16 hour days from May to October.   We would take the bonnet off the upper HP condensate valve, and It got 3 squirts from an oil can in the HP condensate port at mid day.  That was it....But we ran saturated, without a superheater.  We also ran the feed through filtration to remove the oil.     The cylinder walls always look like polished glass.

On My boat "Rushforth", as she can sit quite a while between runs, I oil the cylinders pretty liberally at shut down, just for corrosion protection.    But when I start her back up, I leave the condensate valves open for a while and blow the oil into the bilge, and I run oil absorbent material in the hot well.    Works  OK....not great.   I never run any internal lubrication under steam.  She doesn't need it.   The only time you will hear any noise, is when throttling back, which drops the steam pressure in the cylinder, which by default drops the volume.   The hot cylinder walls will dry the cylinder and you will hear some groans until the cylinder wall temperature comes down, and a condensate film is re established.  Then it will go away.       Opening the starting valve a bit under these conditions hurries  this  along.

Dave

[steamer]

Hi Julian,
 Looks like you have a plan....& a cunning one at that!
On the superheated steam front, and at the risk of getting flamed......in our loco's its doubtfull that we actually get any superheat, or if we do very little! Ok the reason.....you can't superheat wet steam.....in industry boiler makers go to great lengths to REMOVE any intrained water as the steam exits the boiler via cyclone separators prior to the steam going to the superheaters.
In our size we tend not to have any form of water separator or if there is it's pretty crude. Our superheaters more than likely just tend to dry the steam & in doing so increase the volume available & hence we can run notched up & do get the benefit over non superheated fitted loco's.
Now this isn't based on any hard testing but on long discussion over a number of years talking to other loco nuts & working with boilers in the full size petrochemical industry

Right dones his helmet & drives under a rock!

Cheers Kerrin

Very True Kerrin   I agree   And if any superheat at all...it's pretty mild...and more of a dryer......hope there's room under that rock for two!!

[ChuckKey]

I think you may wish to look at some of the research that has been done in the past, particularly by Jim Ewins. Under a sufficient load to get his loco working relatively efficiently, and using firebox radiant superheaters, he measured a steam temperature of 1750F (954C). This is considerably more than is achieved in full size.

[steamer]

I think you may wish to look at some of the research that has been done in the past, particularly by Jim Ewins. Under a sufficient load to get his loco working relatively efficiently, and using firebox radiant superheaters, he measured a steam temperature of 1750F (954C). This is considerably more than is achieved in full size.

If you put enough heating surface in you can do anything you like....that's not the point.   The rest of the system has to be able to operate at those temperatures!....1750F has steel glowing red...The packing has to be able to run there, your lubrication, all of it.    Not for the average joe looking to run his Tich on the club track on a Saturday.   Bronze cylinders would fail very quickly, the paint anywhere near it would burn off....

...and no...it would still not even come close in efficiency as an internal combustion engine....

with Steam in our back yards,   think smiles/mile....not Miles per hour...

Dave

[Steamer5]

Hi Dave,
 Sure is plenty of space, you'd be most welcome! We are not having the best summer, day temps around 20 C.

ChuckKey,
 You dont by chance have a reference to Jim's article do you? Be interested to have a read, 954C is pretty HOT!.
Last place I worked we ran 100 bar steam at 525 C so Like Dave said, you paint wont last long!

Just to throw another spanner in the works down this part of the world on this side of the Tasman there is a "debait" on the use of dublex for boilers. Our Aussy cousins are forging ahead & have quite a few under construction & running, this side there is only a couple built, they were used I understand to prove the design code. Anyway one of the boilers was fired as hard as possible, all 3 safety's lifted & the best firebox inner wall temp they could get was approx 280 C, Bet the fire was a LOT hotter!

Cheers Kerrin

[steamer]

Hi Dave,
 Sure is plenty of space, you'd be most welcome! We are not having the best summer, day temps around 20 C.

ChuckKey,
 You dont by chance have a reference to Jim's article do you? Be interested to have a read, 954C is pretty HOT!.
Last place I worked we ran 100 bar steam at 525 C so Like Dave said, you paint wont last long!

Just to throw another spanner in the works down this part of the world on this side of the Tasman there is a "debait" on the use of dublex for boilers. Our Aussy cousins are forging ahead & have quite a few under construction & running, this side there is only a couple built, they were used I understand to prove the design code. Anyway one of the boilers was fired as hard as possible, all 3 safety's lifted & the best firebox inner wall temp they could get was approx 280 C, Bet the fire was a LOT hotter!

Cheers Kerrin

20C!...we've got 8" of fresh snow!!

[Steamer5]

Yeah gods Dave how do you cope!  sounds like you better get Doc at.ound with his snow blower!

It's only snowed once here in my memory! Mind you the mountain gets its far share!

Cheers Kerrin

[steamer]

Yeah gods Dave how do you cope!  sounds like you better get Doc at.ound with his snow blower!

It's only snowed once here in my memory! Mind you the mountain gets its far share!

Cheers Kerrin

We got 7 feet in 3 weeks in 2014.....better be a big snow blower!

[ChuckKey]

You dont by chance have a reference to Jim's article do you? Be interested to have a read, 954C is pretty HOT!.
Last place I worked we ran 100 bar steam at 525 C so Like Dave said, you paint wont last long!

It was originally a paper read to The SMEE, and later published in Model Engineer, March-April 1966 (which is the year before my library starts), but also reported in 'Model Locomotive Boilers: their design and construction' by Martin Evans, MAP, 1969.

I have quoted it wrongly. That temperature was of the superheater itself, not the steam, which was up to 620F, and which admittedly sounds more like it. This is still a somewhat higher degree of superheat than is usual in full size (the saturated steam temperature being higher at the higher full size working pressures). He reports that after 9 years and 1000 miles hard running, using a high-superheat grade of Shell Valvata cylinder oil, the pistons were withdrawn to replace the graphite packing. The cast phosphor bronze cylinders and drawn bronze pistons were found to be in excellent condition. (Nothing is said about the packing though.)

[steamer]

OK ....sounds more like it....100 bar  ( about 150 psi) is at 377F   round abouts......  so 620 would be 243  degrees of superheat....

Still....hard on everything and you MUST use internal lubrication with a suitable oil.....and mechanical injection   ( Lube pump)

...and forget paint....gonna get smoked right off...

Dave

[Steamer5]

Hi Chuckkey,
 Thanks for the reference, my copies don't go back that far either, I'll have to check out the club library, think they have ME issues back that far. Yes the temp sounds better.

Dave,
 7 feet! Who delivered the popcorn, 

Julian
 Sorry for kind of hijacking your thread, I hope you have found the banter....er... discussion on superheaters of interest. Keep us posted on how you get on making yours. Getting my stainless ones to fit turned into a mission, easy a making the wet header bush, had to do it twice, melted the first trying to silver solder the tubes in! Then the gentle tweaking to get the tubes to be central & the bush to fit & seal to the boiler bush took awhile to sort. Hope you have better luck!


Cheers Kerrin

[Barneydog]

Got a bit of a plan. My son in law has access to some offcuts of stainless tube but the smallest is 15mm diameter so he bringing me a couple of feet. Plan is to lay the tube in the superheater tube through the the boiler and above the fire. Input from the regulator will be a copper tube through a cap of some kind into the stainless tube and then just lay in the stainless to within half an inch or so of the fire end. A cap of some sort on the end to turn the steam back. A short copper tube at the other end to direct the steam to the cylinders. Displacement lubrication supplied with wet steam from a globe valve on the manifold to add lube just before the cylinders. Any obvious problems? May just be worth a go just to see if it works. Benefit will be ease of construction and copper tube can be bent easier to align with fittings in the smokebox. Stainless outer tube should avoid any sagging tubes in the firebox.

Julian

[Jo]

It was originally a paper read to The SMEE, and later published in Model Engineer, March-April 1966 (which is the year before my library starts), but also reported in 'Model Locomotive Boilers: their design and construction' by Martin Evans, MAP, 1969.

Page 252, 18th March 1966 tests carried out on a LBSC designed Minx: There were a number of substantial changes from the original design including the Stainless steel superheater sticking 7" into the firebox. Super heat tests were conducted at 270 deg F, 320 deg and 307 deg.

Jo

[Alex]

This is one of those things which gets into a superheated argument - apologies for the pun.

I'm against superheaters for models - not that they don't do *something*, but that we don't need them.

1) I've got one locomotive in which the superheater flue is plugged solid, and it runs just fine, until more of the remaining tubes get clogged with ash. (the olde LBSC non-radiant superheater, gunked in)

2) I've got another that the original owner removed the superheaters - for what ever reason.

3) A friend with a Sweet Pea had superheaters leak, so removed them, and does not notice the difference.

As mentioned above, lubrication of superheated steam is an issue, from my days licensed as a full-size locomotive guy, ISTR that an issue was lubricating oil burning ("carboning" was the term) in the piston valves, and steam oil lubrication was one of the scientific issues to resolve of the day.

Last thing! Look at the Raritan design - no superheater, no lubricator! Just squirt in some oil at the beginning and end of the day - so easier to make, and maintain.

Whatever you do will be what you do, and will not be the "wrong" direction. Have fun!   

[Barneydog]

Many thanks Alex,
My plan is to build a superheater and fit it. The pipework in the smoke box will be such that it can be removed and either another superheater fitted or a bypass pipe fitted to give plenty options. This gives the options of non superheater or various designs to determine design and/or necessity.
Lube will be adjustable displacement type feeding in after superheater to the cylinders. Steam supplying the lube will be non superheater.
Both these should give me full flexibility for steam and lube. Also gives the opportunity to build a selection of superheaters and try them.

Regards

Julian