What is valve trim?

Talking about the valve trim, the internal elements of a valve are collectively referred to as the valve trim.  The trim typically includes  a  disk,  seat,  stem,  and  sleeves  needed  to  guide  the  stem.    A  valve  performance  is determined by the disk and seat interface and the relation of the disk position to the seat. Because  of  the  trim,  basic  motions  and  flow  control  are  possible.    In  rotational  motion  trim designs,  the  disk  slides  closely  past  the  seat  to  produce  a  change  in  flow  opening.   In  linear motion trim designs, the disk lifts perpendicularly away from the seat so that an annular orifice appears.

API 600 TRIM NUMBER CHART
Trim # Seat Disc Backseat Stem
1         410 410 410 410 410
2         304 304 304 304 304
3         F310 310 310 310 310
4         Hard 410 Hard 410 Hard 410 410 410
5         Hardfaced Stellite Stellite 410 410
5A       Hardfaced Ni-Cr Ni-Cr 410 410
6         410 and Cu-Ni Cu-Ni 410 410 410
7         410 and Hard 410 Hard 410 Hard 410 410 410
8         410 and Hardfaced Stellite 410 410 410
8A       410 and Hardfaced Ni-Cr 410 410 410
9         Monel Monel Monel Monel Monel
10       316 316 316 316 316
11       Monel and Hardfaced Stellite Monel Monel Monel
12       316 and Hardfaced Stellite 316 316 316
13       Alloy 20 Alloy 20 Alloy 20 Alloy 20 Alloy 20
14       Alloy 20 and Hardfaced Stellite Alloy 20 Alloy 20 Alloy 20
15       304 and Hardfaced Stellite Stellite 304 304
16       316 and Hardfaced Stellite Stellite 316 316
17       347 and Hardfaced Stellite Stellite 347 347
18       Alloy 20 and Hardfaced Stellite Stellite Alloy 20 Alloy 20

Note: 410 material is the same as 13Cr or F6 trim.