Fisher NPS 12 Instruction Manual page 11

Instruction Manual
D103553X012
CAUTION
To prevent damage to the valve cavity, packing box wall, and packing surfaces, observe the instructions in the next three
steps.
10. Cover the opening in the valve body to protect the gasket surface and prevent foreign material from getting into
the valve cavity.
11. Remove the packing flange nuts, packing flange, upper wiper, and packing follower (keys 5, 3, 12, and 13, figure
4). Carefully push out all the remaining packing parts from the valve side of the bonnet using a rounded rod or other
tool that will not scratch the packing box wall. Clean the packing box and the metal packing parts.
12. Inspect the valve stem threads and packing box surfaces for any sharp edges that might cut the packing. Scratches
or burrs could cause packing box leakage or damage to the new packing. If the surface condition cannot be
improved by light sanding or honing with a tool similar to an automotive brake-cylinder hone, replace the damaged
parts.
13. Remove the covering protecting the valve cavity, and install a new cage gasket (key 11, figure 5 and 6), making
sure the gasket seating surfaces are clean and smooth.
14. Re-install the trim parts by following the Trim Replacement section. Install a new bonnet gasket (key 10, figure 5
and 6).
Note
Proper performance of the tightening procedures in step 15 compresses the bonnet and cage gaskets (keys 10 and 11, figure 5
and 6) enough to seal the body-to-bonnet joint.
The bolting procedures in step 15 include--but are not limited to--ensuring that bolting threads are clean and evenly tightening
the hex nuts onto the studs in a crisscross pattern. Because of the boltup characteristics of the gaskets, tightening one nut may
loosen an adjacent nut. Repeat the crisscross tightening pattern several times until each nut is tight and the body-to-bonnet seal is
made.
Note
Stud(s) and nut(s) should be installed such that the manufacturer's trademark and material grade marking is visible, allowing easy
comparison to the materials selected and documented in the Emerson/Fisher serial card provided with this product.
WARNING
Personal injury or damage to equipment could occur if improper stud and nut materials or parts are used. Do not operate or
assemble this product with stud(s) and nut(s) that are not approved by Emerson/Fisher engineering and/or listed on the
serial card provided with this product. Use of unapproved materials and parts could lead to stresses exceeding the design
or code limits intended for this particular service. Install studs with the material grade and manufacturer's identification
mark visible. Contact your Emerson Process Management representative immediately if a discrepancy between actual
parts and approved parts is suspected.
15. Lubricate the stud bolts (key 15, figure 5 and 6) with anti-seize lubricant, slide the bonnet over the stem and onto
the bolts, and secure with the stud bolt nuts (key 16, figure 5 and 6), using accepted bolting procedures during
tightening so that the body-to-bonnet joint will withstand test pressures and application service conditions. Refer
to table 4 for bolting torque guidelines.
Large ET and ED Valves
July 2014
11