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Boat Forum / Cruising / March 2006Valves and galvanic action
My boat has a tee off the saltwater cooling intakes that can act as an engine driven bilge pump. The tee is copper pipe with the hoses coming up from the thru hulls. On the leg of the tee is a brass valve that has a hose that reaches down into the bilge for pumping. My problem is the corrosion from galvanic action between the copper tee and the brass valve that controls the bilge suction hose. Can anyone tell me how to stop the corrosion of the valve? The one I have in my hand is almost completely pink because the zinc has completely dissolved. Ideas? Gary Brass doesn't need any galvanic corrosion to go bad in salt water and zinc won't protect it. The problem is that it is full of zinc which disappears leaving it sort of copper Styrofoam. Put in a proper bronze valve.  SignatureRoger Long Gary, it takes more than two dissimilar metals in an electrolyte (saltwater) for galvanic action to occur. The two metals must be connected electrically, usually by a wire. So unless your copper and brass fittings are wired together, which obviously they should not be, they will not generate galvanic currents. As Roger has pointed out, the brass may be self-corroding. Chuck > My boat has a tee off the saltwater cooling intakes that can act as an > engine driven bilge pump. The tee is copper pipe with the hoses coming [quoted text clipped - 11 lines] > > Gary If the copper pipe is fed directly to the brass valve they are connected together. Use bronze or possibly plastic if you can find a suitable sea water rated GRP fitting. Alec > If the copper pipe is fed directly to the brass valve they are connected > together. Use bronze or possibly plastic if you can find a suitable sea > water rated GRP fitting. > > Alec The valve is inside the boat and just controls whether the suction from the bilge is on or not. It is only exposed to salt water on the inside at one end (as the raw water crosses the tee) normally. I think I'd like to try a marelon valve in it's place. Comments? >> If the copper pipe is fed directly to the brass valve they are >> connected together. Use bronze or possibly plastic if you can find a [quoted text clipped - 8 lines] > > Comments? I'd favor high quality bronze ball valve over marelon. The latter requires periodic lubrication a couple of times a year. Forget to lube and it can freeze causing the handle to snap off. Good bronze valves seem to last forever. YMMV. Good luck. Chuck Gary, It is very difficult, if not impossible to electrically isolate every component. It is possible to not use copper and brass in salt water. You should NOT use dissimilar metals without a sacrificial anode and I will point out that plastic valves are not allowed in engine spaces under Loyds 100A1 and IMO standards, if below the waterline. If however, you have a plastic boat, you are screwed anyway. Steve > My boat has a tee off the saltwater cooling intakes that can act as an > engine driven bilge pump. The tee is copper pipe with the hoses coming up [quoted text clipped - 11 lines] > > Gary > Gary, It is very difficult, if not impossible to electrically isolate every > component. It is possible to not use copper and brass in salt water. Agreed. You > should NOT use dissimilar metals without a sacrificial anode This surely does not follow from the first sentence. There is a significant leap of analysis between accepting the near impossibility of isolating every component and reaching the conclusion that dissimilar metals should therefore not be used without a sacrificial anode. Using a sacrificial anode requires that the protected metal be connected electrically (usually with a wire) to the anode. I think one might even say that it is very difficult, if not impossible, to electrically bond every protected component to the anode. But that doesn't suggest that we should not protect where necessary. Fortunately, in the case of a metal valve connected to a non-metallic hose attached to a metal tee, electrical isolation is all but guaranteed. Unless the valve came into direct contact with the metal tee, good isolation would be had. The seawater inside the hose does NOT provide the electrical connection between the tee and the valve required for galvanic corrosion. and I will > point out that plastic valves are not allowed in engine spaces under Loyds > 100A1 and IMO standards, if below the waterline. If however, you have a > plastic boat, you are screwed anyway. Had to read that a couple of times before I caught on. Good point, Steve. Chuck > Steve > [quoted text clipped - 13 lines] >> >>Gary > My boat has a tee off the saltwater cooling intakes that can act as an > engine driven bilge pump. The tee is copper pipe with the hoses coming [quoted text clipped - 11 lines] > > Gary Thanks for all your advice. I replaced the valve with another brass valve. The bronze ones were twice the size and more than twice the price and the chap at the store said they wouldn't last twice as long. At $11, I can afford to change the bilge suction valve every two or three years. It is back together. So you couldn't afford a $22 valve? You need to get out of boating. > So you couldn't afford a $22 valve? You need to get out of boating. If you carefully read my post you would have noted, it was also twice as big and wouldn't last twice as long. There is more to value than price. You need to think. >If you carefully read my post you would have noted, it was also twice as >big and wouldn't last twice as long. There is more to value than price. > >You need to think. I think he was. The point that I heard was "penny wise, pound foolish". Bronze will last more than twice as long, just about forever in fact. And it will also mean never having to say I'm sorry to interested parties like your insurance company. Failed valves on a boat are a sinking asset. >>If you carefully read my post you would have noted, it was also twice as >>big and wouldn't last twice as long. There is more to value than price. [quoted text clipped - 9 lines] > > Failed valves on a boat are a sinking asset. It wasn't a thru hull valve. Gary babbled: > If you carefully read my post you would have noted, it was also twice > as big and wouldn't last twice as long. There is more to value than > price. If you by them books and they eat the covers, not much you can do. Lew >> Failed valves on a boat are a sinking asset. >> >It wasn't a thru hull valve. Was it not part of your engine cooling water plumbing, and therefore indirectly coupled to a thru hull of very large capacity? The amount of bilge pumping actually done by a 20 hp engine may mean that a scrapped bicycle pedal powered centrifugal pump could provide better service along with hidden benefits like excercise. A bilge pump properly used need only move water sideways, not up to a high point. A retractable tail hose down to the sea makes pumping easier, and is syphon safe if used with supervision. This is intended for efficient emergency use only, right? Having an emergency drive system coupled to pedals might actually be of some use, especially if a generator can also be attached to revive a dead battery. Sonds like a dinghy project, to me. Terry K |
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