我覺得這個現象最適合的情況是 /l/ 加 後元音 /u/ 時，隻有在這種情況下，/l/ 音可以省略
例如：
Revolution:
Volume;
Volunteer;

Rethinking/rewording on this:

/l/ sound can be ommited in some words but cannot be replaced with /r/ sound, although the sounding organ (tip of the mouth) is in the position of /r/ sound: