A valve plug assembly adapted for sealing engagement with a seat ring. The valve plug assembly includes a valve plug having a sealing disk adapted to engage a seating surface the seat ring. The seating surface of the seat ring has a primary portion with a primary angle of any one of about 20 degrees to about 45 degrees and a secondary portion extending from the primary portion with a secondary angle of about 10 degrees. A retainer is coupled to the valve plug and includes a body having a first portion, a second portion, and a side extending from the first portion to the second portion at one of an angle of about 30 degrees to about 45 degrees. So configured, the stress acting on the sealing surface is reduced, increasing the service life of the sealing disk.