Dezincification?

This is a picture of a clack valve removed from my 7¼" gauge Hunslet. It has been installed for about 3 years and the copper boiler is always left full of rainwater. I install my fittings using blue Loctite but when I removed this one part of the threaded portion got left behind in the bush. I was able to unscrew that portion fairly easily. It was about the same length as the stub that remains and retained its threads fairly well. All of my fittings have been purchased from three regular ME suppliers over several years but I cannot recall which one I bought the clacks from otherwise I would go back to them for advice. My concern is that this might be a case of dezincification but could that be the case since the portion left behind was in fairly good condition. I am concerned about the situation of the other four fittings which are below the waterline. Any advice would be very much appreciated.

Brass?

A JLS member had a safety valve go into orbit when he tapped it to get the ball to seat, and it sheared at the bush.

He was at the Station ready to take passenger aboard and everyone jumped at the sound and sight of the boiler suddenly releasing its pressure.

Quite something to witness.

Geoff - Yes his valves where brass.

Edited By OuBallie on 10/08/2015 17:42:28

I wonder if these are cast parts? Mainly because of comments I have seen in older sources - "good quality milled brass" which I assume means entirely made of the usual brass bars from a reliable source.

I've gained the impression that when brass is cast for serious purposes it needs to be closely controlled.

John

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It looks like de-zincification because of the copper colour and what looks like porosity or at least a granular appearance. A common occurence with cheap boat skin fittings, which should be made of bronze or at least DZR brass. It should be less common in freshwater environments (salt water being a more effective electrolyte than fresh) but the elevated temperature is probably a factor in this case.

If it was me I'd take off all the fittings involved and remake them from bronze, but that's probably not what you want to hear.

Rain water can also be acid, but certainly looks like it has last its zinc and you are left with soft copper granules.

I've now removed all of the fittings below the waterline and none show any deterioration. They have all been in the water-filled boiler for about 3 years. I've also tried to file the stub of the suspect clack and it seems to file as if it were bronze/brass rather than copper! So I'm a bit confused!! I suspect I don't have a dezincification problem but maybe a clack where the mounting stub was poorly machined? However, when I removed the lower part of the water gauge, the end of it and the bush were both covered/blocked in a white paste type of material. When I removed the paste and left it in the air to dry it crumbled to a white powder. I posted a previous query **LINK** which may be related to this?

Today I have spoken to the boiler maker (over 450 boilers to his credit) and he cannot think of any explanation. His boilers are made using water soluble flux and the number of steamings I have done since buying the boiler (with a blow down after every steaming) would, I'd have thought, cleared out any residue.

Not really sure where to go from here (except to Bristol tomorrow!)

Hi Dennis,

How do you add the **LINK** to another post ?

Paul.

Paul, use the link icon in the edit box (planet with a bit of chain) and paste the link into the dialogue that appears

Neil

Hi Neil,

Well I didn't know that! - I just cut and pasted the URL of my previous topic into the body of my text.

These computers are too clever by 'arf. Most impressive.

As far as the problem is concerned, my next step is to blow the boiler down completely from hot to try to flush out anything in the boiler which is soluble in hot water but not cold.

Dennis

Edited By Dennis Rayner on 14/08/2015 16:51:01

Try ordinary kettle descaler, nice an gentle and if you do have some furring up the fizz will tell you .

Neil

If you use, 'Cillit Bang' it will leave it as bright as a new key according to their advert on TV.

Clive

Good evening Dennis,

Looking at an enlarged photograph of your defective check valve, I can say with almost certainly the cause is dezincification, its discoloration to almost a copper colour together with the friable appearance of the remains are consistent with dezincification. The cause being the material the check valve was made from, brass and in all probability what is referred to as screw rod, my advice is for all fittings below the water line to be made from a non zinc bearing material, drawn bronze being most suitable. The process of dezincification is an electronic action where by the zinc becomes the sacrificial anode where the copper of the boiler forms the other component. Filling the boiler with rain water is not advised due to the unknown impurities it may contain and in all probability will be measured as mildly acidic. Boilers should be blown down at the end of the day thus removing any impurities, but importantly removing any dissolved acids that have accumulated during the days steaming.

To sum up then, no brass below the water line and regular blowing down at the end of the day and if a steel boiler it is essential to add a treatment to the feed water.

Regards,

Bob