Jul 10, 2009|
Question

Dear Dr. Brew,

I'm new to BUNN coffee makers and bought a used CWTF-35 made in 2002. Upon set-up I noticed a water leak and traced it to the water coil fittings at the tank bulkhead. Taking the flare fittings loose, I found that the copper flares had nearly completely disappeared where they contacted the stainless steel elbows, and that is where the leaks were coming from. This was found on both of the stainless steel elbow/copper tubing flair interfaces. The flared fittings at the other ends of the copper tubes, where they joined brass fittings were in perfect order.

It appears that a galvanic corrosion process caused the copper to fail at the stainless steel contact point on the elbows. Since this was only a 7 year old machine, and appeared to have seen little use, I am puzzled. I'm a mechanical engineer, so I am familiar with dissimilar metal galvanic corrosion problems, but usually they involve ordinary steel and aluminum. I am considering replacing the stainless steel fittings with brass fittings to prevent future leaks. Is this a problem that is typical of BUNN machines? I don't want to have to re-plumb the machine with new copper lines every 5 years or so.

v/r,
Gary

Answer

Dear Gary,

Thank you for your E-mail. We'll try to help with the issues that you mentioned below. To begin, the fittings and nuts are brass, either nickel or tin plated. They are not SST. If they are SST, then someone changed them without using BUNN parts.

We are not too sure why the copper flares have disappeared. As this was a used machine, it may be that someone cleaned the machine with the wrong cleaner or disassembled the parts and then cleaned them in a cleaner that is aggressive toward copper. It may be also that the parts were re-assembled and over-tightened by quite a bit, therefore thinning the copper down. It is just very difficult to determine without knowing more of the history of the service of the machine. It is also unknown why the machine was sold used, perhaps it was due to an issue as mentioned above.

We have used these parts and materials in combination for many, many years and just do not have a field issues with them. SST, tin, nickel and copper are fairly close to each other on the galvanic tables.

Hopefully you will have many years of good service from your BUNN coffee brewer.


Happy Brewing,
Dr. Brew

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