Northampton clung on for a point, although Vale had them on the ropes for most of the second half.
The Cobblers had the best chances in the first half, with Chris Martin having to make some fine saves.
But in the second half it was the Northampton keeper, Chris Dunn, who was forced into some desperate saves.
One he couldn't stop was Justin Richards' 55 minute penalty, after Tom Pope crumpled from a challenge from Paul Rodgers.
But Vale's downfall was conceding a quick equaliser 3 minutes later, Leon McKenzie heading home Marcus Hall's cross from the left.
Abdul Osman was then sent off, a straight red for what looked an innocuous challenge on Doug Loft right in front of the ref.
But despite the goalmouth scrambles, Northampton hung on.
Vale drop to 7th. They need a string of good results to come along quickly.