Mixing metals may or may not be a problem depending how close or far apart they are on the galvanic chart. Aluminum is near the top of the chart making it an anode between the two and more likely to corrode. However, brass is about half way down the chart which is a good thing. Also keep in mind the valve will be screwed into a weld boss likely with Teflon tape or some other material. I wouldn't think it would lead to a big problem. That's my input.
Keith and Lisa Ward
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