Ball Valve Seized Postmortem

[nightjar]

Many thanks to all who provided advice on replacing my seized ball valve. The offending valve gave up fairly easily and in the end I did not need to apply heat. The through hull fitting was in good nick and not replaced. Thats the good news ! Having removed the old valve I decided to investigate further with the assistance of the boatyard vice and a large spanner. The shell of the valve can be unscrewed by applying heat and lots of force with the spanner. The threads that screwed into the other half of the valve were so badly eaten away that over 50% of the circumference just came away, a disaster waiting to happen. There is no sign of pinking (dezincification) just a dull rusty surface where the threaded flange had cracked away some time ago. This valve was the silver bodied variety seen in chandelers and was fitted as original equipment 7 years ago. I am now checking the 9 other similar valves with a more critical eye but they show no tell tale signs like the valve just replaced. A one off or should all these valves be replaced ?

 

[boatmike]

Was the offending valve on the seawater intake to the engine by any chance?

 

[nightjar]

Yes, sea water intake to engine.

 

[boatmike]

Thought so!
Very often this one suffers electrolysis because it is connected to the engine through the seawater that runs through it. This can cause it to be anodic. Make sure you replace it with a genuine gunmetal bronze one. 10 to 1 the one you have replaced is tonval or brass. If you have inspected others and they are not similarly affected it is probably because they are not in circuit with the engine. If they are brass or Tonval (same thing) I would replace them anyway frankly even if they are OK.... Better still fit a Blakes combined valve and seacock on the seawater intake and bin the ball valve..... Expensive but safe....

 

[nightjar]

Mike,
Thanks for your reply, you know a lot more than me on this ! I have fitted a new ball valve, the most expensive one I could find in the local chanders. I think its DMZ not sure, its certaintly not silver and its got a green handle not red. Don't know if that had any significance.

 

[isandell]

Blakes valves are brass.

And where can you get bronze ball valves?

Ian

 

[aidancoughlan]

I searched around a lot for seacocks to replace the 20-yr old ones on my boat, and after a frustrating search, www.aquafax.com were the only supplier (that I found) that had clear information on their website (in PDFs format), including references to standards and Llyods certification etc.

I bought DZR ball valves (really de-zincification resistant brass) from their range, but there are gunmetal ones there too, and the new fangled (but expensive) plastic ranges from Forespar. Prices were slightly more than some other suppliers, but at least you know what you are buying.

I found them to be very helpfull with sizes, specs etc.

www.ecsmith.com also have a range of DZR brass seacocks (slightly cheaper if I recall), but didnt have the same level of info to back them up.

ps. usual ... no connection to www.aquafax.com, satisifed customer etc.

 

[boatmike]

Blakes valves are made of an alloy which is resistent to de-zincification and have been proven over many years. They are also a massive one piece casting with no weak points in the design like ball valves. Yes indeed it can be said to be a variety of brass rather than bronze but then so are lots of other things like your propeller.
You can buy Lloyds approved bronze valves from accredited suppliers like Valvestock but they are expensive. For most uses DZR will suffice. My personal preference is to use Blakes on critical areas like engine coolant intakes.

 

[dickh]

I have been told by my local surveyor that the green handled ball valves are OK and are Bronze/DZR or similar. Certainly NOT Brass/Tonval. I've just replaced a skin fitting and I inspected the (green) handled ball valve carefully and it appeared to be fine - no sign of dezinctification - so I replaced it with confidence.