Boiler fittings - is brass OK?

Hi all,

and how about copper bushings? Is copper ok for that?

Hi All

I have made the regulator body out of Naval Brass as per the drawings for my Less Warnett 9F, what are your thoughts on that

Stan

I dare say that copper is ok from a materials compatability point of view but it does not take a thread easily and the threads tend to be weak, especially after brazing the bushes in and annealing the copper.

Much better to use PB, but not one with lead in it as mentioned by someone else.

It's all a matter of how much lead. Gunmetal and Colphos both contain lead, but a lot less than leaded bronze. The BS for leaded bronze states that it can only be silver soldered with special measures, so even tho' I've got away with it in the past I wouldn't use it for boiler bushes. Manufacturers data sheet for Colphos says it can be readily silver soldered, which bears out my experience.

Whether the screw in bits need to be bronze depends on your water quality. This has been covered in ME in the past. For the little extra expense I'd use Colphos, drilling holes in drawn PB1 is a complete pain in the whatsit

Hello all,

This question is of interest to me because I am nearing completion of a Trevithick Dredger engine to the design by Tubal Cain (see hpoto album). I hope to run the engine in steam, but not very frequently. The design has the entire end plate of the boiler in brass, and brass is also used for the cylinder, which is mounted submerged inside the boiler, and for parts of the flue tube. Tubal Cain (Tom Walshaw) did not mention dezincification in his articles in 1987 because I suppose,he considered it as a display model.

I was concerned about the problem, and managed to find a research paper in which measurements had been made of weight loss from brass samples of different compositions exposed to water under various conditions (heat, stirring and so forth). To summarise, there was a weight loss measured of 0.25%, increasing to 0.5% with galvanic contact with copper, in an exposure time of 2700 hours.

To me this is worth noting but does not prohibit running my boiler in steam, provided the duration is short and also that I drain it completely after each steam session. I doubt if I will ever approach as much as 20 hours exposure, never mind 2700 hours, for this small engine intended mainly for display with the occasional half-hour steam up. So, I think I will get away with it.. I have not yet pitched this argument to my club's boiler testers, though. I have used bronze for the bushes and fittings, Mainly for the better strength of the threads.

It would be quite different in an engine intended for regular longterm use, and I would not dispute that brass is best avoided in this kind of service.

Paul

Edited By Paul Horth on 05/02/2016 14:42:13

A little off topic but when people are silver soldering what melting temperature silver solder is usually used?

The reason I ask is that brazing to me means a gas plus blown air torch and temperatures up to circa 8 - 900C or more Approx as I just do it, or have done at work, school too. I see what is generally called silver soldering as being done at significantly lower temperatures and soft soldering even lower.

The question crops up from noting that many bronzes state excellent solderability and only good for brazing and wondering where silver soldering fits in. More like soldering I would have thought.

John

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Silver solders vary according to the % silver content, lowest melt temps are 630 degrees C + ranging up to around 800C. Typical Flux melting is just below 600 C.

You will be using the high silver (55%} at the lower temperatures. Either way it is still a brazing process.

I would still be interested to know what temperature silver solder people use on boilers.

John

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Regarding bushings:

the reason i'm trying to find alternative is the availability of bronze bars in small diameters (at least in my location). It is so expensive that i can't pass by the idea to use 20mm dia bar to turn 8mm dia bushings... such a waste!

Next idea is stainless steel - how about connection SS with copper? SS can be silver soldered, is strong and easily obtainable. Is there any unwanted galvanic phenomena stopping me from doing it?

As to brass bushings and thread strenght: i can make them longer and thus stronger...

Paul Horth - your input is very interesting! I'm not going to steam my boiler 8 hrs a day. Assuming occasional use and that 2700 hours you've mentioned it is good information for me. After all i can design bushings in such a fashion they can be re-threaded to the next size after that... 2700hrs and change fittings. Hey, this is insane

Bogus,

I don't know where you live, but Chronos can supply bronze bar in small diameters and will ship orders outside the UK.

Thor

I thought KWIL answered that.

It is quite common especially on large boilers where there will be several heats of various sub assemblies to start off with a silver solder at the higher end of the temperature range and as the work progresses use lower melting point solders so that previously completed work does not melt so solders between 630 and 800deg melting point are used.

For small boilers one solder can be used and that would tend to be in the lower temperature bracket as its easier to reach the required temperature which is the 55% that KWIL said or old stock of Easyflo which melts at a similar temp.

J

Why would you bother using brass, that boiler etc will/may be around long after you have turned up your toes, and if it's passed on, it would be nice if it was 100%. A mate got a boiler, along with a Stuart Turner V10, it is pre 1930, and the bushes seem ok, but the safety valve bush is loose, I, suggested that it is probably best not to repair it, as I,m not sure of it's construction. Ian S C