What is disk facing valve and vavle body seat ring (gate valve) for?

I am doing a analysis of the component in the gate valve and this two ring confuse me. Seat ring: ring forming a seat, eg. the part of the valve where the closing element 'sits down' or fit against to close the valve.The moving gate is here the closing (moving) element. A part forming the seat can by definition never be mounted on the closing (moving) element, only on the counterpart (on the valve body).NB! For all valves (part of) the sealing is mounted on the moving closing element (or originates from prepared surface of..), and is in some cases held in place on the closing element by a ring (clamping ring). This is then often given names as seat sealing or seat sealing clamping ring or similar. This must be understood as a sealing construction FOR the seat, and not confused with the seat or seat ring.
From the original1checkvalve
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