Galvanic corrosion on isolated brass fixtures

b_arrington

b_arrington

Well-Known Member
GOLD Sponsor
Feb 21, 2007
3,483
Setauket, NY
Boat Info
Back Cove 37
AB Ventus 9VL
Engines
Cummins QSC 8.3 600
If you have brass shutoff valve inserted into a hose that carries salt seawater, is it subject to galvanic corrosion? Should it be bonded, or would it be OK?

Here's the situation. I have 3 air conditioner system on my boat. They are fed by a single raw water pump, with individual supply lines coming off a manifold. When it comes time to winterize it is difficult to isolate each line to ensure AF is in each system. The hoses are tough enough that clamping with a soft jaw pliers doesn't work well.

Adding in a valve for each line to be able to shut 2 loops while one remains open would seem to be solve the issue. Ideally I would use a 1/4 turn PVC ball valve with barbed fittings. The issue is I can't seem to find a combination of PVC valve and barbed fitting to match the 5/8" supply hose. There are plenty of 5/8 brass ball valves readily available, however. Hence my question - I would not want to have the brass valves rot out and leak from galvanic corrosion. I'm just not sure if they would need to be bonded for a "proper" install.
 
Following....I just had the same issue this weekend. The most challenging part of in water winterization every year are the 3 AC units on my boat. This weekend I lost the prime to the AC pump and never got my 3 AC's pinked. Losing prime to that AC pump is always a huge hassle. Instead of endlessly fiddling to re-establish suction I'm going to simply blow out the lines with compressed air and deal with it in the spring. Individual valves would certainly help.
 
They do require bonding. An example is the stainless steel fitting for a raw water pressure sensor on the Onan generator sets which is connected between two hoses. I have lost two of them to pin hole leaks. The third I welded a tab and tied it to the bonding system - three years and no problems. Another example is the exhaust pipe between the riser and exhaust muffler on QSM 11 boats; that pipe if not bonded will form pin holes within a couple of years. Always bond metallic elements.
You can always get 3/4" pipe thread plastic ball valves and install nylon pipe to hose fittings.
 
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Here is pic of another bronze valve that I use to switch the through-hull/strainer between the bridge AC and water maker that originally was not bonded and the hose barbs were corroding off. No problems with this arrangement in the last three years also...
IMG_5199.jpg
 
b_arrington said:
If you have brass shutoff valve inserted into a hose that carries salt seawater, is it subject to galvanic corrosion? Should it be bonded, or would it be OK?

Here's the situation. I have 3 air conditioner system on my boat. They are fed by a single raw water pump, with individual supply lines coming off a manifold. When it comes time to winterize it is difficult to isolate each line to ensure AF is in each system. The hoses are tough enough that clamping with a soft jaw pliers doesn't work well.

Adding in a valve for each line to be able to shut 2 loops while one remains open would seem to be solve the issue. Ideally I would use a 1/4 turn PVC ball valve with barbed fittings. The issue is I can't seem to find a combination of PVC valve and barbed fitting to match the 5/8" supply hose. There are plenty of 5/8 brass ball valves readily available, however. Hence my question - I would not want to have the brass valves rot out and leak from galvanic corrosion. I'm just not sure if they would need to be bonded for a "proper" install.
Click to expand...
I just did this on my boat, I went to LI hardware on vets highway and bought 3/4 PVC valves with threads in them and then got 3/4 threaded to barded fitting ( white plumbing fittings ).
I also use the valve to adjust the water flow to each A / C unit.
Everything the factory installed in my A / C system is all PVC fittings. ( looks like sprinkler fittings )
Going to the boat in a little bit if you want any pictures
 
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ttmott said:
They do require bonding. An example is a stainless steel fitting for a pressure sensor on the Onan generator sets which is connected between two hoses. I have lost two of them to pin hole leaks. The third I welded a tab and tied it to the bonding system - three years and no problems. Another example is the exhaust pipe between the riser and exhaust muffler on QSM 11 boats; that pipe if not bonded will form pin holes within a couple of years. Always bond metallic elements.
Click to expand...

Rats. I thought that would be the case. Thanks for confirming.

You can always get 3/4" pipe thread plastic ball valves and install nylon pipe to hose fittings.
Click to expand...
This is what I was trying to do. I picked up some 3/4 PVC valves and threaded to barbed adapters from Home Depot. My issue is the barb is 3/4 and the hose is 5/8. HD doesn't carry any 5/8" fittings. Might I be able to jam the 3/4" barb in the hose? Yeah, but I don't want to cut the line and find out it won't fit. I think a 1/2" barb may be too small and also restrict the flow.

I guess I'll have to keep searching for the right size.

For reference this is the manifold and AC supply lines I'm dealing with.
upload_2021-10-25_10-42-15.png

upload_2021-10-25_10-44-33.png


And the parts I have now.
upload_2021-10-25_10-45-33.png
 
Spark600 said:
I just did this on my boat, I went to LI hardware on vets highway and bought 3/4 PVC valves with threads in them and then got 3/4 threaded to barded fitting ( white plumbing fittings ).
I also use the valve to adjust the water flow to each A / C unit.
Everything the factory installed in my A / C system is all PVC fittings. ( looks like sprinkler fittings )
Going to the boat in a little bit if you want any pictures
Click to expand...

Pics would be great!

Sprinkler fittings - interesting. I have a (typically) well-stocked sprinkler supply house in my town. I could stop over there and see what they have. My local Ace hardware is quite limited.
 
What ever the final solution is, I'm pretty sure it should not involve the use of brass fittings. Should be bronze or at least a plastic that is used in boats by the builders.
 
Playing devil's advocate here......is this project really necessary to begin with? If you winterize your AC from the sea strainer and turn on all 3 boat AC's why wouldn't pink flow through all 3? Just curious?
 
b_arrington said:
If you have brass shutoff valve inserted into a hose that carries salt seawater, is it subject to galvanic corrosion? Should it be bonded, or would it be OK?

Here's the situation. I have 3 air conditioner system on my boat. They are fed by a single raw water pump, with individual supply lines coming off a manifold. When it comes time to winterize it is difficult to isolate each line to ensure AF is in each system. The hoses are tough enough that clamping with a soft jaw pliers doesn't work well.

Adding in a valve for each line to be able to shut 2 loops while one remains open would seem to be solve the issue. Ideally I would use a 1/4 turn PVC ball valve with barbed fittings. The issue is I can't seem to find a combination of PVC valve and barbed fitting to match the 5/8" supply hose. There are plenty of 5/8 brass ball valves readily available, however. Hence my question - I would not want to have the brass valves rot out and leak from galvanic corrosion. I'm just not sure if they would need to be bonded for a "proper" install.
Click to expand...

Brad,
I hope your reference to BRASS is a mistype and you meant to say BRONZE. For the audience, brass should never be used on anything that sees sea water. Salt water will corrode brass regardless of it being tied into the bonding system. Brass has a high zinc content (above 15%), and as we know, sea water will corrode zinc before any other metal. The process is actually called dezincification, and will turn a brass item into a crumbly porous mess.

I would not recommend PVC either for because of its rigidity. I imagine you have the same long sea water AC cooling runs that I do, and those should be plumbed with nylon, or marelon (sp?) fittings.
 
brewster16 said:
Playing devil's advocate here......is this project really necessary to begin with? If you winterize your AC from the sea strainer and turn on all 3 boat AC's why wouldn't pink flow through all 3? Just curious?
Click to expand...

BC & Sabre don”t plumb multiple AC units with “home run” circuits. I personally believe the guy installing the AC cooling lines gets a bonus for saving on AC cooling hose, so they use long runs of common feeds. I had a manifold added after the pump and added lines so all four of our compressor units had individual feeds as well as discharge lines. This made a noticeable improvement with the AC function, so adding this probable would insure everything gets pinked.
 
The entire manifold and fittings are plastic so install a plastic shut off valve in each line and you're done. I used to over think this stuff but it really isn't a big deal to go plastic where plastic already is. The thru hull shut off valve should be brass or bronze for sure.
 
Henry Boyd said:
BC & Sabre don”t plumb multiple AC units with “home run” circuits. I personally believe the guy installing the AC cooling lines gets a bonus for saving on AC cooling hose, so they use long runs of common feeds. I had a manifold added after the pump and added lines so all four of our compressor units had individual feeds as well as discharge lines. This made a noticeable improvement with the AC function, so adding this probable would insure everything gets pinked.
Click to expand...
Henry, BC at least has changed this since your Sabre was built. Both my BC 34 and 37 had/have manifolds with a separate home run line to each AC unit.
 
brewster16 said:
Playing devil's advocate here......is this project really necessary to begin with? If you winterize your AC from the sea strainer and turn on all 3 boat AC's why wouldn't pink flow through all 3? Just curious?
Click to expand...

I had an experience where one of my AC units had sediment that clogged the line. Since it was an open circuit with 2 other units, I couldn't get enough pressure to clear the line. I was concerned that would be a problem when winterizing - not enough pressure to get the pink all the way through.

Having a shut off would help ensure that the pink flows to each unit.

Also, if you use a Sea Flush their instructions for multiple units are to clamp the other hoses shut. That doesn't seem to work with my hoses as they are a little too rigid. It would be needed because I have 2 units higher than the third; I would ever get the pink "up hill" because it would run out the lowest hose.
 
Henry Boyd said:
Brad,
I hope your reference to BRASS is a mistype and you meant to say BRONZE. For the audience, brass should never be used on anything that sees sea water. Salt water will corrode brass regardless of it being tied into the bonding system. Brass has a high zinc content (above 15%), and as we know, sea water will corrode zinc before any other metal. The process is actually called dezincification, and will turn a brass item into a crumbly porous mess.

I would not recommend PVC either for because of its rigidity. I imagine you have the same long sea water AC cooling runs that I do, and those should be plumbed with nylon, or marelon (sp?) fittings.
Click to expand...

I did mean brass, but I really should know better than to use it on a boat. I know it is a alloy of copper/zinc where bronze is copper/tin and therefore much more corrosion resistant. Brass is so easy to source I had a momentary lapse.

I'm OK with PVC. I confirmed that the manifold is PVC - basically sprinkler parts. My understanding is PVC is preferred over nylon for areas subject to water. PVC's molecular structure does not absorb water, where nylon does. The water absorption can make the nylon fittings stretch and cause leaks. That's certainly not a feature I'd want to introduce to the system. Marelon would be great but in general those seem to have limited availability.
 
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