Assume that silicon is not compatible with the contained fluid. Perhaps the requirement pertains to the soft goods only.  However, as HF eats glass, silicon might not do well in HF service either.
all the valves sold to the GM plant in Ste Therese, outside of Montreal, for their new paint system.  Then I heard there were 'issues' with the lubricants used to assemble the  butterfly valves.  Then I read about all of the GM cars where the paint was peeling off the bodies in large sheets, after only a few months.
Normally Silicone free means that there is no Silicone lubricants used in the assembly of the product.  Even the smallest amount of Silicone can ruin a lot of paint or photographic film.  On paint, it can prevent adhesion and causes a defect called "fish eyes".
You will see the requirement for "Silicone Free" applied not only to the valve, but sometimes to the plant the product is manufactured in.  It is that big of a problem.
There are tests you can do to verify your cleaning procedures are effective. In many cases, the end user will test the product again before they let it into their factory.

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