Tap valve seat

[DIYspanner]

Is it usual to have a ridge in the inner edge of a tap valve seat?

I'd have thought the seat being flat so the rubber washer could sit squarely.

I keep having to replace the rubbers because the seat ridge forms depression in them so when turning on the tap, no water flows till the tap is about 1/2 way open.

Its a kitchen sink mixer by the way.

 

[Burnerman]

It looks pretty worn to me....the brass land can be recut with the appropriate cutter but it does take a while.
John

 

[DIYspanner]

It looks pretty worn to me....
John

Indeed, it's had at least 30 years service. I've been asked to fit a new sink and taps when time permits so that will cure the problem.