A water system with a large manifold feeding 10 3 inch pipes.  Each pipe off the header has one 3" ball valve, about 1 ft of pipe and a nozzle.When complete the valves are commanded closed under full flow conditions.  This is the second valve we have damaged in a short time and the seat damage is in the same exact location on both valves.This is fairly typical of a floating ball valve, happening when staying open with only a tiny fraction of opening.
Regardless of the relatively low pressure before the valve, you will at startup or when the  amount able to get out of the nozzle out is large compared to volume getting through the valve, have atmospheric pressure after the valve. Under theese conditions you will have underpressure (vacuum)over the seat/sealing, probalby also cavitation.
The large pressure difference along the seat perimeter (full water pressure, down to suction at the opening exposed sector) will do things to your valve.
Either you have to control the valve movement, real full open/full closed operation, improve the ball valve construction,or probably best: change to regulating valves that are able to regulate and can withstand the cavitation conditions.
The false operation may becaused by careless operation, rongly adjusted closing elements, damaged or poor construction, particles or firm objects in the stream, damaged seats due to causes above;.. or perhaps a wish to regulate the single nozzels as a feed-stock may have hydraulic conditions giving higher flow at some orifices, lower at others.

MORE NEWS