None of the disc type terms you mention are used in ISO and API butterfly valve standards. The standards use the terms Concentric, Double-Offset, and Triple-Offset. There is also a Single-Offset. From your terms, I can only guess the following:
Swing through = Concentric or Single-Offset
Angle seated = Triple-Offset
These are just guesses only. You should contact the manufacturer who is using these terms for clarification
Suggest you enquire of the butterfly manufacturers or the author of the document from which you gleaned these obscure terms. Perhaps there is a misunderstnading as terms have been translated into Chinese and back again into English.
Some time ago British Airways tested their Russian translators with " The flesh is weak and spirit is willing". The result came back with "The meat stinks but there is plenty of booze"!
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
I, as far as I can remember, has come across the 'definitions' below. I believe them to be 'craftsman' language, more than standards, eg. used by some factories and areas:
Swing through: the disc can be forced through the closed position and move further in the same direction 360 deg. on to the original position. (This is not possible with better constructions with stop contraptions for closed position, but exists. Not found or used for double and triple offset/eccentric valves))
Step seated: self explaining: seat is constructed with one (or more) concentric 'step's'. Purpose: stop disc and/or give better sealing properties og the valve.
Angle seated (I am more unsure here, could refer to double eccentric construction where the disc, when closed, will have a slight angle difference from the centric plane across through the valve body, but have not seen this used for this type of valve.
Best guess is seat, perhaps for metallic seated BFL, where seat has different, but concentric, angle and form from disc closing surface. Purpose: better fit and sealig from valve disc over lifetime.)
