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In my apartment bathroom there's a thick steel pipe with hot water going from the floor beneath through my bathroom and to the store above. There're two pipes welded into that vertical pipe and a towel dryer (actually it's just an U-shaped pipe) connected to them. Each of the pipes to which the towel dryer is connected has a ball cock on it so that the dryer can be shut off.

Now the utility company that services the house tries to threaten me that those ball cocks are unreliable and can break apart at any moment and that will cause flooding my apartment and apartments beneath and I'll be liable for that. The remedy is (of course!) to pay them a fortune for replacing the ball cocks and live happily ever after.

AFAIK there're four major metal alloys used for manufacturing ball cocks and other similar stuff - they are cast iron, brass, bronze and silumin. Cast iron is very rarely used, brass and bronze are used in quality stuff and are quite reliable, silumin is used for cheap imitation stuff and breaks apart easily.

Since I really care I tried to check what those ball cocks are made of. I scratched one of them with a kitchen knife and yellowish surface turned silver, then in about two weeks it turned yellowish again. So I assume that the ball cock is made of brass - yellowish is the typical color for brass parts.

Yet a serviceman from the utility company told me recently that those ball cocks "look like bronze but are made of silumin" and when I told him my findings about the colors change he said "it's emmmm... bronze plus silumin mix". Since brass and bronze look similar I assume he just confuses them and also tries hard to upsell the pricey replacement.

My question is - is it really possible that such "bronze and silumin" mix ever exists and is used for manufacturing a ball cock or is the utility company likely upselling to me?

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This sounds more like a rant about a frustrating experience you had, and less like search for answers. Maybe tomorrow you can revise it and make it better question. –  Jay Bazuzi Dec 28 '10 at 2:56
    
@Jay Bazuzi: No rant intended, I just want to know if there is a real possibility that such ball cock design exists - if it does choosing reliable stuff at shops will become much harder. –  sharptooth Dec 28 '10 at 6:20
    
I cannot answer your question. If I were confronted with the same problem, I'd bring in my master plumber for advise. A good experienced plumber should be able to ID what you have and replace them fairly easily. Good luck. –  shirlock homes Jan 18 '11 at 11:24
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2 Answers 2

up vote 3 down vote accepted

Well, I cannot find a conclusive answer but I have a very educated guess.

Bronze is an alloy of mainly Copper(Cr) and an additive Tin(Sn). Silumin is an Aluminum(Al) alloy with 12% Silicon(Si). It is highly resistive to corrosion under wet environments.

During the alpha phase of metalic cooling, rapid crystallization occurs that is visable under a microscope at 5 µm. I will spare this answer from the nitty-gritty but with the addition of Sn to a bronze alloy, the hardness increases by 55 on the Brinell test.

Ergo, if you added Silumin to Bronze, there by adding Si to bronze, you make is harder. So it is plausable to say this mixture is used for this application, especially since we are dealing with plumbing.

Spoke with my college chemistry prof. who agrees that this is an entierly possible mixture of transition metals.

(will post pictures once I find them)

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Two years later the utility company admits that they have already replaced all the unreliable silumin ball cocks in the building before they handled the keys to the first tenant and all the yellowish ball cocks are made of brass. They won't admit it, but it's likely they made up all the "bronze and silumin mix" thing for the sake of upselling the replacement. So maybe the mix is technically possible but it's highly unlikely for the following reasons.

Reason one is legal. In this jurisdiction the first ball cock that separates the common piping and the apartment piping belongs to common property is is maintained and serviced by the utility company. So if they don't replace unreliable silumin ball cocks they are liable for damage and that's serious legal risk.

Reason two is technical. Silumin is used for producing ball cocks because it is much easier to mold than other alloys and so it's one of the cheapest and the easiest alloys that can be used in a cheap low-tech process for producing a cheap ball cock that meets no real life requirements. Adding bronze renders this idea useless - the process becomes much more expensive and make no sense anymore.

So maybe the proposed alloy is technically possible, but it makes no sense for producing cheap ball cocks.

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