Don't rule out a freeze up either. It's true a first stage freeze up will result in a usually violent free flow, but if ice forms around the lever and inlet assemply in the second stage, it will act just like the description given above with the air delivery falling off as the lever's range of travel is restricted, and returning as the ice melts in warmer water.
This was almost never a problem with metal cased second stages as the metal case transferred the heat from the relatively warm water into the second stage very efficiently. It does however occasionally happen with plastic cased second stages that are essentially insulated from transferring heat from the surrounding water.
The Sherwood Blizzard uses metal strips in the second stages to capture the heat from your exhausted air to thaw any ice that may try to form on the lever or inlet housing. The second stage is otherwise identical to the Brut in over all fucntion, so the heat transfer strips are apparently quite important in cold water.
This was almost never a problem with metal cased second stages as the metal case transferred the heat from the relatively warm water into the second stage very efficiently. It does however occasionally happen with plastic cased second stages that are essentially insulated from transferring heat from the surrounding water.
The Sherwood Blizzard uses metal strips in the second stages to capture the heat from your exhausted air to thaw any ice that may try to form on the lever or inlet housing. The second stage is otherwise identical to the Brut in over all fucntion, so the heat transfer strips are apparently quite important in cold water.