Does anyone know about the workings of an in-ground pool and vacuums?

We have spent so much time and money trying to figure out why the vacuum cuts out and the waterfall comes to a trickle. We have had all the equipment checked and the pressure, motor, pump are all working just fine but after the water and vacuum runs for 10 minutes it just stops. We have had professional come and check it out and they fix something but that does not solve the problem They throw up there hands and leave. We need help fast. Thanks.