Hayward Phantom w/o booster pump?

Hello - is anyone running a Phantom without a booster pump? I have three returns with valves at the beginning of each so I can adjust the water flow. A Northstar 1.5hp (full rated) feeds three separate 2" lines back to the pool. If I shut off 2 lines I get a scary amount of water gushing out the side return. I can't imagine why I would need a booster pump. Any thoughts??
Thanks,
Scott

What is your filter PSI with the 2 lines shut off? If it is more than 20 PSI, you should be OK.