Pump not priming! Help!

First off i am new to the site and just started a powerwashing business. I built a new setup, 18hp motor general pump ts2021 and a zeromatic unloader. Its gravity fed. Water goes into the pump on the lower end but won’t push out the unloader. Everything is new and should work in theory. But it seems like its not pulling the water. So i put a garden hose to it from a spigot and the water seems to pulsate out the pump. Any help or suggestions are greatly appreciated.