How to increase arm speed?

when ever i am throwing my hardest which is about 70 and then i take a look back at the videos it looks like i am just lobbing the ball but i am really not. so is there a way i can increase my arm speed?

thats good… sorta

it can trick the batter into thinking its a slow pitch then just blow it by them

learn how to use your body weight/ momentum to put everything you can into the ball while staying within yourself. there is no magic bullet. its good you are focusing on arm speed not strength because arm strength has nothing to do with velocity.