The loco from Chennai pulls upto Renigunta, stays dead upto Tirupati at the end, while a new loco is attached at Renigunta to pull towards Tirupati. From Tirupati the loco at the front from Chennai will pull upto Renigunta and detached while the dead loco at end wil! Pull from Renigunta to Chennai. This practice is there for both Sapthagiri and. Chennai exp right from May 2017 or before when I saw in Tirupati.