I’m unsure what you’re referring to as “the eye size”. The “eye” normally refers to that part where the liquid first enters the impeller. I hope you mean the bore of the suction nozzle of the pump, in which case there should always be a reducer at that point from the suction piping that should be at least one size larger than the suction nozzle. If the nozzle is on a horizontal configuration, then the reducer should also be an eccentric design with the flat side on top.

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