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Silver Soldering LG2

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Andrew Johnston04/06/2020 22:40:34
5499 forum posts
647 photos

I'm in the process of designing the starting valve for my traction engines, based on fullsize. For those parts not in contact with steam I plan to use brass. But the body, which will be in contact with full pressure (wet) steam ideally needs to be bronze. The body will need to be silver soldered together from several smaller parts.

I've recently silver soldered some PB102 bronze with some success, but it's a right pain to machine. I've also machined some LG2 gunmetal with excellent results. The starting valve body is going to need some accurate and burr free internal machining, so I'd prefer to use LG2.

But LG2 contains lead, so the question is how does it silver solder? I've found a thread on this forum, from a while back, where it was said to silver solder well. But the internet seems to be confused on the subject. Some commercial organisations says it solders well, but is less good for brazing. I take soldering to mean relatively low temperature with tin/lead solder, whereas brazing includes silver soldering.

What does the collective think?


Paul Kemp04/06/2020 23:28:08
480 forum posts
18 photos


i have successfully silver soldered what was purported to be "gunmetal" in the past. I am sure CuP will provide a definitive answer though.


Michael Gilligan04/06/2020 23:28:39
15712 forum posts
687 photos

This little cog in the collective machine thinks you should visit : **LINK**

... and probably start by downloading this: **LINK**


Paul Lousick04/06/2020 23:46:29
1409 forum posts
540 photos

what is a starting valve ?


Hopper05/06/2020 02:02:03
4530 forum posts
94 photos

You might also contact Keith at CupAlloy . Hes a sometime member on the forum and wrote the book on this stuff , literally. Probably more reliable than the collective unconscious of forums etc. He seems to be very in tune with model issues too.

Edited By Hopper on 05/06/2020 02:04:04

Thor05/06/2020 05:36:20
1229 forum posts
37 photos

Hi Andrew,

I recently used LG2 to fabricate a cylinder for a mill type steam engine. The portblock was silver soldered (brazed) to the cylinder. I experienced no problems, but I have not yet tried it on steam, only compressed air. This page says it is Good for brazing.


Simon Collier05/06/2020 07:08:39
352 forum posts
56 photos

I and fellow members use LG2 for all our boiler bushes, using traditional easyflow type silver solder.

JasonB05/06/2020 07:14:46
18113 forum posts
1995 photos
1 articles

Andrew, quite a few of my 24mm bore engines and even the larger ones use a mix of SA660 ( more lead than LG2), GM, Brass and steel and I have had no problems soldering them together.

The Brazing problems you saw mentioned may be those using oxy-ac where the possible higher temps could boil the lead and the gasses produced will weaken the joint but at the usual silver soldering (brazing) temps it won't happen.


Edited By JasonB on 05/06/2020 07:36:39

Baz05/06/2020 08:37:43
378 forum posts

I have silver soldered LG2 and had no problems at all, I used the old Easyflo rods.

shaun meakin 105/06/2020 09:36:25
42 forum posts
1 photos

Hi Andrew, lead in leaded metals is what is known as 'free lead', ie it is not alloyed but like currents in a cake. As a consequence because of it's low melting temp when brazing it melts and comes to the surface which inhibits brazing alloy flow.

As said here it can be silver brazed but we recommend opening up the joint gap slightly to allow more alloy in thereby combating any flow problems.

Hope this helps but if not please feel free to call us.

Shaun - CuP Alloys.

fizzy05/06/2020 10:08:23
1710 forum posts
115 photos

You will have no problems using Colphos (90), it contains almost the same lead as LG2 but was created with machinability as its focus. It silver solders without any issues.

CuP Alloys 105/06/2020 13:20:44
238 forum posts

To ice Shaun's cake!

I refer to my posting on March 10 on " boiler bush material"

BS EN 14324:2004 "Brazing - Guidance on the application of brazed joints" outlines the potential problem of brazing phosphor bronze. Shaun offers a solution to the problems.

The information contained in this Standard has been judged to be overpriced but it simply forms part of the library of CuP Alloys, the contents of which are readily available to customers.

When you buy from CuP, you get a lot more than just rods and flux!

We look forward to hearing from you


Andrew Johnston05/06/2020 20:57:54
5499 forum posts
647 photos

Thanks one and all for the advice. It's good to know I can use LG2. As said some bits will be made from brass, but the flange that bolts onto the cylinder will be PB102 as I've already got a piece of 5mm sheet. The body will be LG2 as I've got a suitable length in stock. It's a bit oversize, but I might as well use it rather than buy new stock. Money is tight at the moment; not sure I'm ever going to work again due to the current shambles. The valve itself will be made from stainless steel.

It's helpful to know that Easy-Flo is good, as that's what I'm using. I bought a number of rods some while back. Due to previous disasters I've been avoiding silver soldering where possible. But I'm on a roll now! I take note of the bigger clearances and will contact CuP in due course. Even if the solder doesn't flow as well a small fillet wouldn't be a problem as the original part was a casting.


Andrew Johnston05/06/2020 21:17:23
5499 forum posts
647 photos
Posted by Paul Lousick on 04/06/2020 23:46:29:

what is a starting valve ?

That's the official Burrell name, but I prefer to call it a singling valve.

On a compound the engine will not start without assistance when the high pressure piston is on dead centre. The solution is a starting valve which admits full steam pressure to the low pressure valve chest, bypassing the high pressure cylinder. This allows a double crank compound to start as the high and low pressure pistons are not on dead centre at the same time. But on a single crank compound (as I'm building) this doesn't work as both pistons are on dead centre together. The valve still admits full steam pressure to the low pressure valve chest. So the engine can run as a single using the low pressure cylinder - hence my name. Since the low pressure cylinder is larger than the high pressure cylinder more torque, if not power, should be available. The operating button is push to open the valve and is spring loaded closed. I've been told (on the TT forum) that this is how the SCC engines were operated. A momentary push of the button would give a short burst of more oooomph as needed.

None of the above is to be confused with a simpling valve. This is a valve that resides in the cylinder and diverts the high pressure cylinder exhaust to the chimney. Used in conjunction with a starting valve it converts a compound to two singles running in parallel.


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