New sea cock time.. stainless, dzr or Marelon?

[SteveAus]

Can anyone tell me why bronze gate valves are not viewed favourably for use as seacocks. They are not as convenient to use as ball valves as they require multiple turns of the handwheel, but surely this is not sufficient reason not to use them. They are widely available through plumbers' merchants and good quality ones are made entirely of bronze with some DZR internal components. They have a metal to metal seal so the only non-metallic component is the stem packing.
In contrast it appears impossible to buy a bronze ball valve which does not have a plated brass ball with a few exceptions. (Vyv has mentioned that plastic balls are available, and Groco offer a stainless ball although other Groco models have a plated brass ball. There has been mention of Apollo offering bronze balls but I can find no indication of that on their website.)
I am aware of the issues of mismatching threads and possible lack of strength of bronze skin fittings due to their thin walls, but are there any other reasons not to use bronze gate valves?

 

[[70521]]

Half my through-hulls are near the water line. Hitting a log was just an example. Pretty common in the Pacific North West by the way. Also you could hit other things. In the UK, a semi submerged pram may be your object of choice. Or try bumping into a rock even.

My current boat was holed, above the water line, in a previous ownership. According to the accident report it took the force of a 10 tonne vessel's bow hitting the boat on the mooring at five knots with an estimated tide of three knots running through the moorings.

I have a Safety Engineering background and well versed in looking for the improbable to happen, testing what happened when it did and signing products off to be used in the real world. Given the total surface area of the hull and the percentage of that area and the location of the through hulls I consider the risk extremely low. If it does happen I have kit on board that will seal a hole in the hull. It sounds like you have come to a different conclusion and that is not a problem,

I recall a story my late mother told me. She trained as a Registered General Nurse back in the 1950s. On returning to nursing after giving birth to me she was alarmed one night when a hospital doctor placed plastic syringes in an autoclave for sterilization. In the time that she was off work the world had moved on.

 

[vyv_cox]

Can anyone tell me why bronze gate valves are not viewed favourably for use as seacocks. They are not as convenient to use as ball valves as they require multiple turns of the handwheel, but surely this is not sufficient reason not to use them. They are widely available through plumbers' merchants and good quality ones are made entirely of bronze with some DZR internal components. They have a metal to metal seal so the only non-metallic component is the stem packing.
In contrast it appears impossible to buy a bronze ball valve which does not have a plated brass ball with a few exceptions. (Vyv has mentioned that plastic balls are available, and Groco offer a stainless ball although other Groco models have a plated brass ball. There has been mention of Apollo offering bronze balls but I can find no indication of that on their website.)
I am aware of the issues of mismatching threads and possible lack of strength of bronze skin fittings due to their thin walls, but are there any other reasons not to use bronze gate valves?

The big problem with gate valves in a fouling duty is that the gate is opened using a very small section pin in tension. When the gate is closed various marine growths attach themselves to the slide. Turning the wheel strongly enough to move the gate against the shell can cause the pin to break, the valve is now locked closed. More of a problem with a brass pin but perfectly possible with dzr or bronze.

 

[Rappey]

I had a gate valve on my engine intake that I always closed after use.
Had a built in strainer which I could never undo.
Gave it some force one day and the whole fitting rotated in the hull ?
Time for a new one!
Turns out the old gate valve had failed a long time ago in the open position and all my opening and closing was not doing anything !

 

[RJJ]

If you read the instructions for Trudesign, they suggest epoxying into the hull as one method so, it becomes in effect part of the hull.

That was indeed my point, thanks, and was what I have done with mine. The epoxy is the same thickness as the hull; in fact it's thicker than the original as Trudesign's instructions ask for the hull to be at least 20mm thick, so I added a few layers of fibreglass in some places before fitting.

 

[AndyL]

Just looking on ASAP website not a great deal in it price wise between dzr, stainless or marelon.
thoughts on what’s best or the pros and cons of each?

I'd go with Guidi "Non Stick" Bronze Seacock Full Flow Valves Type "ALEX". They are a type of Plug valve, but the plug doesn't turn like a blake's seacock, it rises up and down similar to a gate valve. Importantly it cannot be overtightened. The plug is made of neoprene.

 

[RJJ]

I'd go with Guidi "Non Stick" Bronze Seacock Full Flow Valves Type "ALEX". They are a type of Plug valve, but the plug doesn't turn like a blake's seacock, it rises up and down similar to a gate valve. Importantly it cannot be overtightened. The plug is made of neoprene.

that narrowing of the diameter looks just the thing to catch a particularly big [whatever form of blockage you prefer to imagine]

 

[contessaman]

So somebody touched on it earlier...

my skin fittings (stainless ) are shot too so I’m replacing everything. Is there a reason why one couldn’t use dzr skin fittings with plastic sea cocks?
to be fair I’m virtually a long keeler and where my skin fittings are I can’t imagine they would be struck by something. I would have to ake sure the sling for the hoist doesn’t catch on them

 

[Graham376]

that narrowing of the diameter looks just the thing to catch a particularly big [whatever form of blockage you prefer to imagine]

Don't think it needs to be big, a small buildup on the metal under the cone after several months of being open may be enough to stop it bedding.

 

[dankilb]

So somebody touched on it earlier...

my skin fittings (stainless ) are shot too so I’m replacing everything. Is there a reason why one couldn’t use dzr skin fittings with plastic sea cocks?
to be fair I’m virtually a long keeler and where my skin fittings are I can’t imagine they would be struck by something. I would have to ake sure the sling for the hoist doesn’t catch on them

My surveyor suggested this - I’m not sure why though (I didn’t ask!) and can’t quite see why one would...

I’d worry that adding a bulky and otherwise long-lived composite valve on top of a shorter-lived DZR skin fitting could be a recipe for missing any corrosion and/or deferring replacement beyond the life of the brass fitting (because the valve will almost certainly be working ‘as new‘ long after the skin fitting starts going rotten).

If you epoxy the TruDesign skin fittings in to at least 20mm of laminate, as others have suggested, surely you end up with a stronger overall construction than brass which might start going brittle after a few years?

 

[LONG_KEELER]

Just a thought. Plastic does start to go brittle over time. Fortunately, the usual UV damage will not apply to skin fittings.

It may well be that composite plastics have overcome this. Tufnol resins seem to work well over time in marine applications.

 

[Graham376]

Just a thought. Plastic does start to go brittle over time. Fortunately, the usual UV damage will not apply to skin fittings.

It may well be that composite plastics have overcome this. Tufnol resins seem to work well over time in marine applications.

GRP boats are plastic composites Trudesign have passed many recognised tests such as Tru Design

 

[RJJ]

My surveyor suggested this - I’m not sure why though (I didn’t ask!) and can’t quite see why one would...

I’d worry that adding a bulky and otherwise long-lived composite valve on top of a shorter-lived DZR skin fitting could be a recipe for missing any corrosion and/or deferring replacement beyond the life of the brass fitting (because the valve will almost certainly be working ‘as new‘ long after the skin fitting starts going rotten).

If you epoxy the TruDesign skin fittings in to at least 20mm of laminate, as others have suggested, surely you end up with a stronger overall construction than brass which might start going brittle after a few years?

Yes, but the comparison isn't with brass, but with bronze. Nobody's debating whether bronze is 'king strong, or that brass is strong to begin with and then becomes brittle.

But I agree, the fibreglass (not just "plastic") fitting, epoxied into a fibreglass hull is also 'king strong.

 

[Graham376]

But I agree, the fibreglass (not just "plastic") fitting, epoxied into a fibreglass hull is also 'king strong.

A lot stronger than this one which broke up when I started to take it out, it had passed surveyor's hammer test 12 months earlier but he had suggested changing as age unknown. At a glance, with seacock attached, it looked fine.

 

[Yngmar]

How long is a Tru-Design seacock expected to last? Can't find that info on their website.

Good question. They only say "long life" in the instruction PDF. I would expect them to outlast the boat and/or owner - they're chemically resistant, corrosion isn't an issue and they're not really exposed to much UV either, so the only way in which they would experience any aging at all is probably mechanical wear from opening and closing and that's probably good for a couple ten thousand cycles. I don't expect they would need replacing again in the lifetime of the boat, whatever that may be, unless mechanically damaged from a collision or travelift mishaps. Ours are now 5 years old and show no signs of any wear or other decay and all still operate as easily as the first day. Even the Coppercoat is still sticking to them!

 

[neil1967]

Can anyone tell me why bronze gate valves are not viewed favourably for use as seacocks. They are not as convenient to use as ball valves as they require multiple turns of the handwheel, but surely this is not sufficient reason not to use them. They are widely available through plumbers' merchants and good quality ones are made entirely of bronze with some DZR internal components. They have a metal to metal seal so the only non-metallic component is the stem packing.
In contrast it appears impossible to buy a bronze ball valve which does not have a plated brass ball with a few exceptions. (Vyv has mentioned that plastic balls are available, and Groco offer a stainless ball although other Groco models have a plated brass ball. There has been mention of Apollo offering bronze balls but I can find no indication of that on their website.)
I am aware of the issues of mismatching threads and possible lack of strength of bronze skin fittings due to their thin walls, but are there any other reasons not to use bronze gate valves?

If you look at a gate valve it is impossible to tell if it is open or closed. in an emergency i would like to tell at a glance whether my seacocks were open or closed.

 

[Zing]

....corrosion isn't an issue and they're not really exposed to much UV either, so the only way in which they would experience any aging at all is probably mechanical wear from opening and closing .....

Don’t be so sure about that. I have seen engineered plastics fail for all kinds of reasons. The one that surprised me the most was a nylon component terminally damaged by acid produced by algae. There are lots of other ways:

Polymer degradation - Wikipedia