The largest and most potentially dangerous pieces of "blue ice" have been associated with "donut" valves".
A guess at what the donut valve might be, based on the source of the comment and the object of "blue ice".
The FAA site would likely pertain to airliner operations. A number of "blue ice" incidents have resulted from a plane's lavatory or water closet blue color flush water that leaked out during a flight.  The leaking fluid would freeze on the exterior of fuselage in the sub-zero temperatures of high altitude flight.  Most of the time the "blue ice" would be small enough to melt off when the plane reached warmer air at lower altitudes.  A large or small lump of "blue ice" could fall on anything in the landing path to an airport.  Sometimes the "blue ice" would be so large that it remained attached to the fuselage until the impact of landing on the runway finally jarred it loose.  One instance the airport security guards were called to retrieve an unknown object from runway, and they realized what it was only after it began to melt in their office. 
The "donut valve" might be similar to a rubber pinch valve that might be applied in slurry or solids services. The rubber sleeve of typical pinch  gate valve probably has more shrinkage to cause seal leaks from low temperatures at a high altitude flight.  A metal seated valve would have better sealing at low temperature of high altitude flight operation.

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