Vietto, who had not scored a single goal in 2017, broke the deadlock with his first shot for his loan club, slotting home on the rebound after Simone Zaza's header was parried by Las Palmas goalkeeper Raul Lizoain.
The Argentine, on the books of Atletico Madrid, doubled his tally shortly after the restart with a neat dink over Lizoain, before Nemanja Maksimovic put the game to bed with the hosts' third goal - and his first for the club - on 54 minutes.
Vietto saved his best for last, completing his hat-trick on 66 minutes with an audacious effort from around 40 yards out which soared above the Las Palmas backline and goalkeeper before dipping into the net.
VALENCIA (4-4-2): Domenech; Latorre, Gabriel, Vezo, Montoya; Nacho (Torres 67'), Kondogbia, Maksimovic (Parejo 63'), Pereira; Zaza, Vietto (Rodrigo 71')
LAS PALMAS (4-2-3-1): Raul; D. Castellano, Lemos, Garcia, Simon; Gomez, J. Castellano (Herrera 74'); Hernan (Aquilani 62'), Samperio, Halilovic (Tana 80'); Calleri