Marelon seacock failure

[Therapy]

Originally Posted by HopCar

I recently did some research on seacocks to see what their stems were made of as the subject came up in another thread. I checked with Groco, Perko, Buck Algonquin and Apollo. I consider them all to make quality products. All but Apollo use brass stems. Non of them seem to de-zinc. I don't know why. Maybe they are not exposed to enough water?


.

Sheesh!

[HopCar]

Sheesh indeed. But what's puzzling to me is that with my two and Sailor Chicks one that's three Apollo failures of the "better" bronze stems. By the way, Apollo also uses brass stems in their marine ball valves. They only use the bronze stems in their flanged seacocks.

[sailvayu]

And one more reason to use real flanged sea cocks not ball valves on a through hull or flanged plate.


There you have it!

[HopCar]

Wayne that looks like a brass stem that has lost some zinc. I don't see the sponge effect that a really badly dezinced stem would have. It also looks like an Apollo ball valve. Am I right on it being Apollo?

Just to throw in another variable, Groco uses stainless steel stems on the seacocks they make in the USA. Yeah I know, crevis corrosion. It doesn't seem to happen with the alloy they use.

[sailvayu]

I do not recall the brand I am guessing Apollo but not sure. It happened during a survey and I took a couple of pix and moved on. It was an old Bertram 28 but I do not think this was original as I later fond what looked like an original gate valve.

[HopCar]

That was eaten up not just twisted off.
Sailor Chick, are we looking at electrolisis?

[sailvayu]

Yes it is galvanic corrosion (electrolysis is for plating metals or removing hair) It fell off in my hand as soon as I put light pressure on it. This boat had some issues with galvanic corrosion in other places as well.

[Boracay]

I've been fitting the Trudesign ball valves to Boracay as the old ones go past their use by date. I believe they are particularly suitable for a steel boat.

So far no worries...

They have added skin fittings and tails to their range.

I like to see more chandlers stock these.

[sailvayu]

These are still ball valves on thru hulls, not proper seacock. The only proper seacock has a flange bolted to the hull. I have seen thru hulls eaten completely away by stay currant, the only thing that kept the boat afloat was the flanged seacock, if it had had ball valves on thru hulls it would have sunk. I have also seen a boat run on rocks that had the thru hull sheared off but it had ball valves and sank. The hull was not breached if it had a proper seacock it would not have gone down.

[sailorchic34]

Originally Posted by sailvayu

Yes it is galvanic corrosion (electrolysis is for plating metals or removing hair) It fell off in my hand as soon as I put light pressure on it. This boat had some issues with galvanic corrosion in other places as well.

+1

The nice pinkish color is a great indication that the zinc had been sacrificed out of the brass via galvanic corrosion.

Really the difference between some brass and some bronze can be just a few % more or less of zinc in the valve. The better grades of bronze have very little zinc. Though what some manufacturer call bronze is very close to brass in some cases.

Plus sometimes a bad batch of alloy makes it though the shop. Even Groco has had that problem some years back. Plus in apollo's, well CONBRACO case anyway there are different grades of valve that look about the same to the eye.

I remember a YWCA I designed years ago where the brass shower valve control lever on all the showers failed after 8 months due to micro galvanic corrosion of the yellow brass. The cost the manufacturer.

[estarzinger]

Originally Posted by CHM

I thought about a foam plug and changing it, but have noe experience doing it that way.

honestly it's not that hard to change in the water. Since it's so small you could easily shape a dowel to be a precise tapered fit to the thruhull (or stuff nurf foam in it). And since it's just the screw on model, all you have to do is screw off the old one and then screw on the new - perhaps about a minute total.

[HopCar]

Am I correct in thinking that since galvanic corrosion (thanks for the correction) was the problem with that stem, it wouldn't matter if it was brass or bronze? Galvanic corrosion can destroy either metal.
Is lossing zinc from brass a different process than galvanic corrosion?

The alloy of brass that Apollo / Conbraco uses in their 70 series ball valves (sold to the marine trade) is about 37% zinc.

[Maine Sail]

Originally Posted by HopCar

Am I correct in thinking that since galvanic corrosion (thanks for the correction) was the problem with that stem, it wouldn't matter if it was brass or bronze? Galvanic corrosion can destroy either metal.
Is lossing zinc from brass a different process than galvanic corrosion?

The alloy of brass that Apollo / Conbraco uses in their 70 series ball valves (sold to the marine trade) is about 37% zinc.

You can request their 85-5-5-5 bronze valves. This is the bronze that is most often used in seacocks. The Apollo tri-flanges are 85-5-5-5 (often referred to as three-five bronze or eighty-five three-five). Groco and Spartan etc. are also 85-5-5-5..

[sailvayu]

Bronze has less zinc than brass. As others pointed out it all depends on the chemical make up of the metal but in general bronze is much better because it has much less zinc. Zinc is less noble meaning it gets taken away first as the electrons flow from one piece of metal to another. This leaves the metal with voids like swiss cheese and of course weakens it. Sailorchic is correct, a sure sign of this is the pinkish color you see. So brass with more zinc will suffer damage faster. In the case of this valve I suspect a localized galvanic cell within the valve itself which I am sure was made worse by a poor bonding system and general poor maintenance. A valve within inches of this one appeared fine.

[skipmac]

Originally Posted by HopCar

I recently did some research on seacocks to see what their stems were made of as the subject came up in another thread. I checked with Groco, Perko, Buck Algonquin and Apollo. I consider them all to make quality products. All but Apollo use brass stems. Non of them seem to de-zinc. I don't know why. Maybe they are not exposed to enough water?

In fact the only two stems I've seen broken from any of these manufacturers were a couple of bronze Apollo stems. Both were from 2-1/2" Seacocks and broke when the owners used extra force to free a stuck valve. They just looked undersized for the job. That was a long time ago and I bet they've fixed the problem by now.

What about seacocks from Spartan? I never see them mentioned when seacock discussions come up. I know nothing about them except they claim to be bronze and, as far as I know, are the only company still making tapered plug type seacocks.