O'Sullivan has already had a month-long spell at Vale Park this season but he returned to the Championship club at the start of March after making just one substitute appearance. Vale boss Rob Page has brought the 20-year-old back to Burslem after allowing Chris Lines to leave for a loan stint at Bristol Rovers, where he will spend the remainder of the campaign. "We're delighted to have secured Tommy's services, he's a very gifted young player," Page told the club's official website. "Everyone was impressed with how he performed in his last spell, both in training and in our win at Walsall as a substitute. "With Chris Lines having gone out on loan, we felt it was important to get someone in and Tommy ticks all the boxes in terms of the type of player we were after.
"I'd like to thank Cardiff City and Russell Slade for their co-operation in helping us get this deal done as quickly and smoothly as possible." O'Sullivan trained with Vale on Thursday morning and should be available to play this weekend when Swindon visit Vale Park. He will remain with the League One side until April 14.
Good Luck to him