hayward stops after 5 mins

Trying this hayward pool vac ult ra and after 5 mins it stops. I notice on pool pump that when i started with acuum hose attached to skimmer and lever pointed to skimmer only the pressure shows about 4.5 and vacuum moving really good . So then about 5 minutes go by and pressure shoots up to about 13 and vacuum has stopped moving...any ideas, sugestions...id really appreciate it......nothing obstructing the bottom of vacuum, backwashed did all i could think of but keeps doing same thing. When i back wash the water looks pretty clean..