Forspar Marelon Valves in engine room ? Any surveyors can help ?

fishermantwo said:
Bronze will de zinc as well. Mate lost a blade off a two bladed propeller recently. In the remaining prop there was only a cross section of real bronze about 5mm across. The rest was like pink cheese.
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It is simply impossible for bronze to dezincify, as bronze is an alloy of copper and tin. LG2 and LG4 contain about 5% zinc, mainly to act as a deoxidant when casting, but loss of this small amount would not affect the strength of the casting. Brass used for castings contains about 40% zinc.

There are several alloys with misleading names, Manganese bronze, from which many propellers are made, is simply a brass with a small addition of manganese. Admiralty bronze is another, although more recent versions of it are usually referred to as Admiralty brass, a 70/30 brass with 1% tin. Even more confusingly, Americans call bronze 'red brass'.
 
vyv_cox said:
It is simply impossible for bronze to dezincify, as bronze is an alloy of copper and tin. LG2 and LG4 contain about 5% zinc, mainly to act as a deoxidant when casting, but loss of this small amount would not affect the strength of the casting. Brass used for castings contains about 40% zinc.

There are several alloys with misleading names, Manganese bronze, from which many propellers are made, is simply a brass with a small addition of manganese. Admiralty bronze is another, although more recent versions of it are usually referred to as Admiralty brass, a 70/30 brass with 1% tin. Even more confusingly, Americans call bronze 'red brass'.
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Absolutely spot-on, Vyv. The trouble is that "bronze" is a catch-all phrase - most of the fittings sold as bronze are, in fact, Admiralty bronze (or more correctly Admiralty brass). Bronze is a luxury metal, the earliest alloy - originally copper/tin - and has always been reserved for the upper reaches of society. Unfortunately there are too many imitations and without the necessary research facilities it's impossible to know what you're getting. One of the phrases in my boat-description is "all underwater fittings are bronze" patently untrue of the tail I removed.
 
From various correspondents in Europe and elsewhere it seems that DZR brass ( it is a brass, not bronze ) is not widely known outside UK. It was invented here for the plumbing industry to combat corrrosion of standard brass by soft waters common in the west of Britain. I guess that not too many other countries come across the problem, so the alloy has not spread far, although it is made to an international standard.

Many European boatbuilders source their skin fittings and ball valves with Guidi, in Italy. Theirs are made from leaded brass, of which I have seen many failures. The reasoning of the builders is that nobody has reported a failure back to them, so they have no reason to change. Would you report back to your boat builder if you replaced a seacock?
 
charles_reed said:
I've just changed the, admittedly brass, toilet seacock for a glass-reinforced plastic one. It weighs 20% of the old one and has a 20-year warranty. It's made in NZ. So called DZR (of which the tail was made) was definitely de-zincified after 22 years.
Blakes valves are unobtainable in Greece, 316 stainless ones are available (at €75), the plastic one cost €68. The comparable Blake's unit from ASAP supplies is £158, and as far as I know has no lifetime guarantee.
Case rests.
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Thanks for not answering my question. You need to put things in context. The OP has metal ball valves at the moment, which he suspects are suffering from dezincification, although it is not clear whether it is the valve or a fitting. The most obvious direct replacement is DZR (and DZR or bronze fittings), not plastic. Current prices for different types of valves (from ASAP) are as follows - all 1 1/2", but the differential is similar for the other popular size 3/4" DZR £38, Bronze £50, Plastic (Marelon) £63. Blakes are more expensive as you rightly say, but are not direct replacements and would mean significant work to fit in an application that currently has skin fittings and ball valves.

So, back to the problem - what to replace suspect valves with. In the UK (where the OP is) it has to be DZR on technical and economic grounds. There is no advantage with a GRP boat in paying the significant extra cost to fit plastic valves. 316 is not a good choice as you have to change all the fittings and you still have the potential of crevice corrosion, particularly in the threads.

The reason why non metallic valves are common in other countries, particularly in USA and down under is simple. DZR is not readily available and the substitute for bronze is plastic. Therefore that is the product that is made and marketed locally. This is simply not the case in the UK where the chosen substitute for bronze is DZR. If that were not available, almost certainly somebody would have set up to make plastic valves.

In your case in Greece, I would have made the same choice as you because when I tried to buy DZR valves there, nobody could guarantee they were not brass. My solution was in fact to buy valvea in UK and take them out to my boat there so that I was sure what I had.
 
machone said:
One worry I have about the forespar fittings is that the recommended method is to fit direct without gasket, using sealant! Is there a sealant suitable for an engine room? The valves have a webbed/meshed underside which fills with sealant and seems to me the worst design for a watertight seal. Fitting is a two person job as the valve itself screws into the fitting. Anybody any recommendations on gaskets or not?
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I've written a blog post on my experience with fitting Marelon seacocks. todayiboughtaboat.eu/?p=403 if it's of any help

I found so far that the sealant has done the job as per the Marelon youtube instructional video. I think the web mesh that you're referring isn't a worry as you should attach it to a backing pad anyhow.

My only advice would be to not to forget to coat the threading on the skin fitting with sikaflex, as I have one very small dribble on one out of the 3 seacocks, momentary lapse of concentration. (the others replaced by the previous owner are all fine).

The seacocks I replaced were seized, and from what I understand is that the plastic seacocks are maintenance free, which is another reason for my choice in Marelon.

Anyhow that's my experience so far. I'll keep an open mind and see what happens. If my boat sinks I'll be sure to post it on ybw :D
 
timmygobang said:
The seacocks I replaced were seized, and from what I understand is that the plastic seacocks are maintenance free, which is another reason for my choice in Marelon.
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"Maintenance free" does not mean that you can ignore them. It just means you cannot easily take them apart when they seize - for the same reason that metal cased ball valves seize. That is a build up of deposits around the edges of the hole in the ball if they are left open or on the ball if they are left closed. If you do not exercise them regularly, they will seize.
 
To the op
Instead of looking at the thread (which may or may not be giving you an informed reply) why not just ask the manufacturer if their items are suitable for the situation you propose
At least when you are drowning you will have a piece of paper to show to the insurance co
 
Tranona said:
"Maintenance free" does not mean that you can ignore them. It just means you cannot easily take them apart when they seize - for the same reason that metal cased ball valves seize. That is a build up of deposits around the edges of the hole in the ball if they are left open or on the ball if they are left closed. If you do not exercise them regularly, they will seize.
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I don't ignore them, I always open and then close them when I leave the boat as a matter of routine. Just checking up on the literature, the hoses need to be removed and the ball valve lubricated. Saying maintenance free was hastily typed, it is Monday afterall ;)
 
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