Lapping Metal Seats - Emerson Fisher HS Instruction Manual

HS Valve
June 2019

Lapping Metal Seats

A certain amount of leakage should be expected with metal-to-metal seating in any valve body. However, if the
leakage becomes excessive, the condition of the seating surfaces of the valve plug and seat ring(s) can be improved by
lapping. (Deep nicks should be machined out rather than ground out.) Use a good quality lapping compound of a
mixture of 280 to 600-grit. Apply the compound to the bottom of the valve plug.
To ensure correct alignment of the valve plug, bolt the bonnet in place during the lapping process. Removal of the
packing facilitates the lapping. A simple handle can be made from a piece of strap iron locked to the valve plug stem
with nuts. Rotate the handle alternately in each direction to lap the seats.
On double-port valves, the top ring normally grinds faster than the bottom ring. Under these conditions, continue to
use lapping compound 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 lapping compound on the seat ring that is not leaking and polishing
compound on the other ring. This procedure grinds down the seat ring that is not leaking until both seats touch at the
same time. Never leave one seat ring dry while grinding the other.
After lapping, remove the bonnet, clean the seating surfaces, reassemble, and test the valve for shutoff. Repeat the
lapping procedure if leakage is still excessive.
Figure 9. Actuator Mounting (Type 657 Actuator Shown)
NOTES:
YOKE LOCKNUT IS REPLACED BY EIGHT CAP SCREWS AND
1
NUTS ON 5-INCH YOKE BOSS (1 AND 1-1/4 INCH STEMS).
A1507/IL
12
CAP SCREWS
STEM CONNECTOR
YOKE LOCKNUT
1
TRAVEL INDICATOR DISK
STEM LOCKNUTS
Instruction Manual
TRAVEL INDICATOR SCALE
D100381X012