I wanted to get a VariValve vent, but I think there's a lot of water in the system (because I get hammering sounds, and have experienced a lot of water coming out of old, failed vents, on all 3 of my radiators, which are on the 2nd floor of a 3-story, 6-unit building), and I read in another thread
that these don't have floats.
(The latest vent that spilled was a Jacobus with a #4 port.) The building management is unresponsive these days but I think a repair person said something like that there's nothing that can be done about the water - it's an old building. I like the VariValve, because Heat-Timer advertises that the flow rate can be set up to 0.72 CFM, while the next fastest one I know of, Gorton #D, does about 0.45 CFM. I have a Jacobus with a #D port on one small radiator and feel that it would be best to be able to go a lot higher, on a very long radiator that's in a colder room.
Screwing off the port doesn't look like it would be a lot faster than a Gorton #D, because down the Jacobus opening it doesn't look bigger than its #D port opening, and I haven't found test results for Jacobus. So I had the idea of somehow having a float valve in series with a VariValve. I didn't find one on the Web, so I wonder if anyone knows of any float valves that don't constrict air flow more than the VariValve.