Can I mix gunmetal and DZR fittings?

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ChasB

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Just bought two strainers at a much reduced price from ASAP. They are made of gunmetal.

Owing to an error in measurement the ports are 1.5" BSP, and the hosing on board is 1.25".

I could replace them but I'd lose over £100 in the process, plus the hassle.

I've scoured the internet but can't find any hose tails that go from 1.5"BSP to 1.25" - though every other combination of sizes appears to be available!

However I've found this Aquafax DZR CONNECTOR 1 1/2"BSPT - 1 1/4" HOSE thingy.

Will this work? Or is there a danger of galvanic corrosion?

The boat is primarily used in fresh water, with (at most) a week of salt water each year.

I've also found this 1 1/2" BSP for 32mm or 38mm ID Hose Plastic Skin Fitting. Would it be completely barmy to consider this?
 
No I dont believe there will be any problem mixing DZR brass and a bronze such as gunmetal. Especially in fresh water. Take a look at this galvanic series to see how close brass and bronzes are http://www.corrosionsource.com/handbook/galv_series.htm
Is there any problem with ordinary brass for that matter in fresh water ~~~ plenty of brass fittings on domestic water systems!
Plastic skin fittings are ok in my book but I dont think I'd mount a heavy object like a filter on them.
 
Cheers Vic.

I found this in my researches:
"DZR brass would have been resistant to the form of corrosion exhibited by the fittings from Random Harvest. The failed fitting was not made of DZR brass.
Brass is a relatively cheap and strong material, so it could appear an attractive alternative to more durable alloys. The item which failed cost about £6. One made from dezincification brass (DZR brass), silicon bronze, or gunmetal, might cost two or three times as much, but even that cost is still only a minute fraction of the value of the vessel.
Using brass for underwater through-hull fittings is a false economy. DZR brass is more expensive because after machining it has to be heat-treated to remove the chemical micro-structure vulnerable to dezincification.
However, discussions with UK wholesalers indicate that brass has been in common use for underwater fittings both within the UK, and on continental Europe, since about 1983. Many hundreds of thousands of items have been sold, and the wholesalers are unaware of any serious dezincification failures"

" Gunmetal: Hard, strong copper-tin-zinc alloy that is easily cast. The alloys now usually contain lead to improve machining characteristics and bearing properties."

Seems encouraging, but I found nothing referring to putting these alloys together in water and any consequent galvanic corrosion.

(But really - isn't the internet wonderful? What would I have done a few years ago? Answer: spent the eveniong down the pub! /forums/images/graemlins/blush.gif )

As to the plastic fitting - I didn't explain. I meant cutting the large retaining ring off (on the left) that would normally go on the outside and thus leaving only the thread which would then go into the strainer's port. The hose would then slip over the other end. Some kind of sealant would be added - sikaflex or plumber's tape? The fact that water is being sucked in would mean there's no pressure pushing these things apart. However there is a lot vibration from the engines (even though they're not in direct contact) so I wondered how nylon fittings would fare.
 
[ QUOTE ]
I found this in my researches

[/ QUOTE ] Been reading MAIB reports then! You know know all about "Tonval"

The galvanic series is the key to predicting if metals are compatible or not. The greater the difference in potential between them the greater will be any galvanic activity. The table I linked to is particularly nice because it has a voltage scale on it not just a list of metals and alloys, although it is confused a bit by having three voltage scales based on three different reference electrodes. The usual ones given if any are those against a calomel electrode but of course standard electrode potentials and the electrochemical series that you'll find in chemistry text books are referenced to a standard hydrogen electrode.

In that table you can see that all the common brasses and bronzes are within about 0.1 v of each other so you'd expect very little if any galvanic action. Just no volts to drive any current round the circuit. No current ~~ no corrosion.

Regarding plastic fittings the best material is probably "Marelon" a glass reinforced DuPont nylon. There is a whole range of fittings including skin fittings, sea-cocks, filters & hose tails available but I don't see any problem with adapting other plastic skin fittings to do what you want. There should be at least as sound as the hoses you'll be fitting to them.
 
DZR is a poor material to use and if you can avoid it i would.
Tonval or genuine gun metal is the way to go.
Most of the real shiney fittings you see in swindeleries these days are DZR and shouldent in my opinion be sold to be used in and or on boats.
I did a number of years as a surveyor and these fitting were a total menace

Hope this helps

Joe
 
If you did a number of years as a surveyor YOU were a menace!

Tonval is low grade brass and should NEVER be used, Any form of bronze is good but Tonval is NOT bronze. DZR brass is a very good second choice to bronze and in most cases quite adequate. There is also absolutely no problem mixing bronze and DZR.
 
There are only two problems with plastic. 1 is mechanical strength. Skin fittings or ball valves can stress and crack due to overtightening of threads and or take a knock and break off on the inside. There is also a problem with swelling due to water being absorbed which can be minimised using Delryn (Ertecetal H). I don't know what material "Marelon" is but I think its glass reinforced nylon. I have no direct experience of it but would fit a proper Bronze or DZR seacock rather than chance it frankly.
 
Thanks everyone for all the info.

Vyv that is a very interesting report. Required reading I'd say! When I first got this boat I used to think that maybe I worried a bit too much about details like this, but I've come 'round to thinking that in boating you really do need to. If you screw up the vessel really can sink when you're not there!

As to glass reinforced nylon - it may be strong but my unfortunate experience is that it can also be brittle and will crack if actually bent. I think the DZR fittings at £6 ea are good enough, but I reckon the non-reinforced nylon ones would have worked just as well.

Cheers!
 
thumbsup.gif
 
[ QUOTE ]
I don't know what material "Marelon" is but I think its glass reinforced nylon.

[/ QUOTE ] [ QUOTE ]
"Marelon" a glass reinforced DuPont nylon.

[/ QUOTE ] "Zytel" to be precise but its only a name to me and probably to you. Quite agree with you about strength but, that's why earlier on I said I would not screw a heavy fitting like a (metal ) strainer onto a plastic skin fitting. OTOH they don't dezincify and personally not had any problems with ageing ( fittings that is not me ~~~ that's another story)

BTW the "Random Harvest" report can be found in its non predigested and regurgitated form at http://www.maib.gov.uk/cms_resources/random%20harvest.pdf
 
they don't dezincify and personally not had any problems with ageing ( fittings that is not me ~~~ that's another story)

You and me both.... I think I am probably "work hardened"
My daughter called me an old curmudgeon the other day.... probably right!
 
Yes indeed boatmike you are correct
Been a while since i got involved in this ongoing situation with bronzes but i got it round the wrong way without checking /forums/images/graemlins/smile.gif
DZR is ok if it is actually what it says it is
But to be on the safe side just use gun metal i would say
On another note i dont think there was a need to be so insulting mate
An honest mistake
Joe
 
Assume you are using these as water intakes for your engine cooling systems where the pumps have an intake of 1.25 inch. In which case the easiest way round the problem is to use a stepped connector, made out of plastic from Vetus to reduce the hose diameter. There is no load on the fitting, it is simply let into the piping. Part no HA 3060 page 91 in catalogue.
 
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