Mixing DZR brass and bronze?

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BabaYaga

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Hi all,

wonder if it would be OK to mix DZR brass and bronze in an assembly of fittings for an under water through hull?

I recently ordered and received some DZR valves and fittings from ASAP Supplies, as I want to replace two old underwater through hull fittings, that could well be made of plain brass.
Unpacking the various items, I discovered something that has been discussed in previous threads, for instance in this one:

http://www.ybw.com/forums/showthread.php?361441-BSP-not-what-it-seems&p=4205861#post4205861

Namely that all the items – skin fittings, valves, T-piece, hose tails – have parallel BSP threads EXCEPT for the hex nipple, which has a BSP tapered thread.
I have read on here that using a tapered male thread into a parallel female thread is acceptable, but I would like to avoid this in order to reduce the total length/height of the assembly as much as possible.

ASAP has a hex nipple of the same size in bronze that has parallel threads. Could I use this together with the other DZR items without worries?
 
I think the truth about galvanic corrosion between bronze and DZR brass is probably unknown. My best guess would be that the reaction would be extremely slow or non-existent. There is very little potential difference between the two in the galvanic series in seawater table. Dezincification in brass is an internal reaction, little affected by external anodes, so it seems likely that arresting the reaction by adding arsenic will probably mean that no reaction takes place.

It's just my best guess, so no lawsuits, please! :)

Not quite sure why you need the nipple, I thought the ASAP range was pretty comprehensive.
 
Thanks Vyv,

I found that reply quite reassuring.
I will go ahead with a bronze nipple then, if a DZR one with parallel thread cannot be found. I have emailed ASAP about it.
It is for joining the ball valve to the T-piece, as both these have female threads.
 
BabaYaga said:
Thanks Vyv,

I found that reply quite reassuring.
I will go ahead with a bronze nipple then, if a DZR one with parallel thread cannot be found. I have emailed ASAP about it.
It is for joining the ball valve to the T-piece, as both these have female threads.
Click to expand...

It is common plumbing practice I think you will find to use a tapered male thread into a parallel female. You'd not do it with high pressure, hydraulic and maybe not pneumatic systems You'd use parallel male threads ( or all tapered) but they would then tighten onto a joint washer; fibre, copper or compressible according to application.

I agree with Vyv about the likely lack of any significant galvanic action between bronze and DZR and I think you will find bronze or gunmetal skin fittings are commonly used with DZR valves, Maybe the bronze is just that little bit stonger than (DZR) brass making it attractive for what could be the weakest component in the assembly.
 
Hex nipples will be BSPT, If you want to stay DZR then get a running nipple they are available in DZR from ASAP among many suppliers in varying lengths and running nipples are BSPP. I use them with two flanged back nuts to carry hoses through bulkheads at low level.
 
Last edited:
Thanks for the tip about the running nipple. Will consider.
I guess the really painful thing about it is the size and price.
I need 1 1/4", the item ASAP stocks is 150mm long, weighs close to 0,5 kilo and costs over £21!
Will try other suppliers for something shorter (and cheaper).
 
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