Plat_DownByValue

From ZDoom Wiki

63:Plat_DownByValue (tag, speed, delay, height)

tag: Tag of affected sector 
speed: Speed of move 
delay: Tics before going back up 
height: Amount to lower by 

Lowers a platform by (height * 8) units, waits, and then raises it back to its original position. If tag is 0, then the sector on the line's back side is used.