centrifugal pumps

Can you draw a schematic? Valve sizes, pipe sizes/length, flow meter location?

Name of pump Mfg and Model #'s

pump and fittings proper size this just started recently

Something is collapsing on the suction side. Does the amp draw go down with flow?

Is the impeller securely attached to the motor shaft? No slip? Still no info on your pump.

pump is goulds 8196 suction is 16 inches and has no restriction pump does cavitate flow goes from 1200gpm to 800gpm when autmatic valve is opened more than 53 percent have to close automatic to get 1200gpm back thought mabey restriction on discharge but dont know if is possible to act this way all valves and fittings r original size worked before but not now

ANY check valves anywhere on the system that may have failed?

pump is goulds 8196 suction is 16 inches and has no restriction pump does cavitate flow goes from 1200gpm to 800gpm when autmatic valve is opened more than 53 percent have to close automatic to get 1200gpm back thought mabey restriction on discharge but dont know if is possible to act this way

Is it not starting to cavitate?

Do you have any pressure regulating valves in there.

PRV's may only start working at a minimum flow.

Your delivery pipe may be running over a high point causing a air lock.

To stop us guessing please give more detail.

You say suction is 16 inches. This is a booster pump, not self priming. It must have a positive pressure on the suction head. Has something changed on the supply side to change suction pressure? Is there a point anywhere in the suction side where the plumbing goes higher than the pump that an air pocket could develop? One bad joint or gasket on the suction side will let air in and cavitate the pump. Air could be coming in the shaft seal while running, won't leak water when stopped.