Fisher HPA Instruction Manual page 29

Instruction Manual
D101634X012
Figure 16. Example of Machining the Lower (Valve Plug to Seat Ring) and Upper (C‐seal Plug Seal to Cage) Seating
Surfaces
PLUG
1 0.254 (0.010)
LOWER SEATING SURFACE
REMOVAL OF 0.010 INCH FROM THE SEAT RING
NOTE:
REMOVAL OF 0.254 mm (0.010 inch) FROM THE VALVE PLUG
1
REMOVAL OF 0.254 mm (0.010 inch) FROM THE SEAT RING
PLUS
2
MUST EQUAL 3
REMOVAL OF 0.508 mm (0.020 inch) FROM THE UPPER
SEATING SURFACE IN THE CAGE
4. THESE VALUES ARE FOR EXAMPLE ONLY. REMOVE ONLY THE MINI­
MUM AMOUNT OF MATERIAL REQUIRED TO REFURBISH THE SEATS.
A6781 /IL
5. Using an appropriate tool such as a center punch, stake the threads on top of the plug in one place (figure 14) to
secure the C‐seal retainer.
6. Replace the piston rings following instructions in the Trim Replacement section in this manual.
7. Return the seat ring, cage, plug/retainer assembly, and stem to the valve body and completely reassemble the valve
package following the appropriate instructions in the Trim Replacement section in this manual.
CAUTION
To avoid excessive leakage and seat erosion, the valve plug must be initially seated with sufficient force to overcome the
resistance of the C‐seal plug seal and contact the seat ring. You can correctly seat the valve plug by using the same force
calculated for full load when sizing your actuator. With no pressure drop through the valve, this force will adequately drive
the valve plug to the seat ring, thus giving the C‐seal plug seal a predetermined permanent set. Once this is done, the
plug/retainer assembly, the cage, and the seat ring become a matched set.
With full actuator force applied and the valve plug fully seated, align the actuator travel indicator scale with the lower end
of valve travel. Refer to the appropriate actuator instruction manual for information on this procedure.
C‐seal
RETAINER
UPPER SEATING
SURFACE
(4)
0.508 (0.020)
3
MACHINING OF THE UPPER
SEATING SURFACE MUST
EQUAL THE TOTAL MACHINING OF
THE LOWER SEATING SURFACE
(PLUG PLUS SEAT RING). IF NOT, THE
RETAINER MAY STRIKE THE UPPER
SEATING SURFACE BEFORE THE
VALVE PLUG PROPERLY SEATS ON
THE LOWER SEATING SURFACE.
CAGE
(4)
SEAT
RING
(4)
0.254 (0.010) 2
mm (inch)
HP and HPA Valves
July 2017
29