Intro4u2u

A certain amount of leakage should be expected with metal-to-metal seating in any globe-style valve body. If the leakage becomes excessive, however, the condition of the seating surfaces of  the valve plug and seat ring can be improved by grinding. Large nicks should be machined out rather  than ground out. Many grinding compounds are available commercially. use one of good quality or make your own with a mixture of 600-grit silicon carbide compound and solidified vegetable oil. White lead should be applied to the  seat to prevent excessive cutting or tearing during grinding. In cage-style constructions the bolted to the body with the gaskets in place during the grinding procedure to position the cage and seat ring  properly and to help align the valve plug with the seat ring. A simple grinding tool can be made from a piece of strap iron locked to the valve plug stem with nuts.
On double-port bodies, the top ring normally grinds faster than the bottom ring. Under these conditions, continue to use grinding compound and white lead on the bottom ring, but use only a polishing compound (rottenstone and oil) on the top ring. if either of the ports continues to leak, use more grinding compound on the seat ring that is not leaking and polishing compound on the other ring. this procedure grinds down the seat ring is not leaking until both seats touch at the same time. Never leave one seat ring dry while grinding the other.
After grinding, remove bonnet or bottom flange, clean seating surfaces, and test for shutoff. Repeat grinding procedure if leakage is still excessive.