Lee Bradbury came closest to breaking the deadlock as the pair of First Division strugglers played out a goalless draw in torrential conditions at Fratton Park.
Former Manchester City man Bradbury hit the base of Paul Musselwhite's right-hand post at the beginning and end of an otherwise dull first half.
In the very first minute he cut in from the left-wing before firing against the upright. And he did the same 41 minutes later from a Michael Panopoulos cross from the right.
The Australian substitute made a real difference for the managerless home side who nevertheless remain without a win since October 30.
Vale were indebted to goalkeeper Musselwhite for their point after he made a string of great saves, the best a breathtaking catch at the second attempt.
Musselwhite, who ironically was on Pompey's books as a youngster, also made two fine saves to deny Michalis Vlachos.
Vlachos looked suspiciously offside when Musselwhite saved his point-blank header on 56 minutes, and with quarter of an hour to go Musselwhite tipped another goal-bound Vlachos header for a corner as Portsmouth continued to make all the early second-half running.
Vale had started the second half strongly with Jeff Minton having a 25-yard bullet tipped over the bar for a corner by Aaron Flahavan in the Portsmouth goal.
The visitors continued to huff and puff and forced a string of corners midway through the second half and in the awful weather conditions there was always the chance of a costly defensive error.
Pompey, without the injured Darren Moore, were let off when Jeff Minton flashed a shot wide with eight minutes left.
And Vale, using Matt Carragher at the heart of their makeshift defence, nearly folded with five minutes left when Jason Cundy headed wide after latching onto a free-kick from the impressive Sammy Igoe.