Bi-Metallic Corrosion in a PCP

[rsterne]

I pulled apart a 2260 HPA conversion today and this is what came out.... I had a leak which I was chasing last fall and had used soapy water around the valve screw holes in the hope of finding out if the O-ring on the outside of the valve was leaking.... When done, I used compressed air to blow off the water, but it appears I blew some of the soapy water in between the valve and the tube.... I won't be doing that again....



It looks a lot worse than it is, the valve cleaned up with a bit of steel wool, and the inside of the tube was not pitted, although it did have some light rust marks.... In addition, the corroded area is not pressurized, it is behind the outer O-rings.... However, it does show what can happen when two dissimilar metal are exposed to moisture and then allowed to sit.... Definitely something to be aware of....

Anybody have any brilliant ideas of the best thing to coat either the inside of the tube (ideally) or the outside of the valve with to prevent a repeat?....

Bob

[SeanMP]

Ya Bob there are a couple things we use onboard ship.

Noalox (spelling?) and anti corrosion paste by Grote

http://www.homedepot.ca/product/noal...-in-cap/934874

http://www.grote.com/product.php?product_number=99170

[AirGunEric]

Was it really a bi-metallic reaction- or simple rust because of the water being trapped and unable to dry off?

as it is in the non-pressurized area of the tube and therefore can't ignite- why not use a grease of some sort? (the big problem being- how to get the grease out of the rest of the tube once you have installed the valve- dragging it down the tube and leaving lubricant all along the way).

[rsterne]

Good point, most of it is rust from the tube.... The white residue is aluminum ozide.... However, the water, plus the alkali from the soap, is an ideal medium to produce severe bi-metallic corrosion....

A thin film of grease on the aluminum valve would probably help, because it would be (mostly) contained by the O-rings when you slide the valve into the tube.... I guess you could use a shotgun swap to remove any residue....

Thanks, Sean, for the ideas.... I'll check them out....

Bob