Fill valve slow to shut off completely

[Jeff Johnson]

I've got a Kohler San Rafael toilet (one piece with tank that only extends above bowl by a couple inches). In it, it has a fairly standard flapper type flush valve with a new flapper that seals well. The fill valve is a 1B1X style ballcock valve. It has a new cap, o-ring, and plunger.

On this toilet, the "normal" tube that flows water down the flush valve tube is not used, instead the water is routed through a diverter valve with a secondary float on it. During the first part of the fill cycle, that valve routes water through a tube into the ring around the top of the bowl where it runs out the holes around the periphery of the bowl and down the sides of the bowl. After the tank is partly full, the float of the diverter valve rises and redirects that flow into the tank.

I've got the tank fill height correctly adjusted, the water height in the bowl adjusted correctly, and no flapper leaks. When flushed, the tank fills quickly to about the 98% level, but then the fill valve continues to barely trickle water inti the tank for quite a while until the level has risen the last 1/8" to increase the float pressure enough to fully shut off the fill valve.

Is this normal? It seems to me that the valves should be designed to fill the tank and then "snap shut" rather than closing very gradually.

 

[Reach4]

Slow closing would certainly prevent water hammer. I don't know what normal is for that.

Is that slow closing 6 seconds or 2 minutes?