What does this mean in the ventilation duct?

The first letter of SFK- Chinese spelling word air outlet, also known as prefix, means air outlet.

(JY- 1)- Numbers on the standard map.

750 *(750+250)- The size of the tuyere, the visible surface on the projection is 750, and the invisible surface is 750+250.

10478 m3/h- the volume flow of fluid passing through every hour.

The skin under the tuyere is a very high description.