-7-
Lapping Metal Seats
With metal-seat constructions, lapping of the seating
surfaces can improve shutoff. Use a commercial lap-
ping product or a mixture of 600-grit carborundum and
solidified vegetable oil and lap the seating surfaces of
the valve plug and seat ring (Figures 3, 4 and 5, Keys 25
and 32). Deep nicks should be machined out rather than
ground out.
Follow valve assembly procedures until the cage (as well
as cage retainer and bonnet spacer if used) is in place,
and the bonnet is bolted to the body. Create a simple
handle from a piece of strap iron and lock to the valve
body with nuts. Rotate the handle in each direction to
lap the seats. After rotating directions, remove the bon-
net and clean the seat surfaces. Completely reassemble
the valve according to directions in the Trim Mainte-
nance section. Test the valve for shutoff and repeat the
procedure if leaking is still excessive.
Valve Plug Maintenance
Key numbers in this section refer to the following Figures
in the manual:
•
Figure 3 for Mark EWD Valve Plugs
•
Figure 4 for Mark EWS Valve Plugs
•
Figure 5 for Mark EWT Valve Plugs
Note: If the piston ring (Key 29) or seal ring (Key
50) are being replaced, protect the surfaces of the
ring groove in the valve plug, or any surfaces of the
replacement ring. Scratches in these surfaces may
prevent proper seal of the replacement ring.
Remove the valve plug (Key 25) according to instruc-
tions in the Disassembly section, and proceed as fol-
lows:
Mark EWD – Carbon Filled TFE Piston Ring
a.
The piston ring has a split in one place, and if
damage is visible, the ring can be spread
slightly and removed from the groove in the
valve plug.
b.
When installing a carbon-filled TFE piston ring,
spread the ring slightly apart at the split. Install it
over the stem and into the valve plug groove.
Ensure the open side faces along the stem,
depending on the flow direction and as shown
in View A, Figure 3.
Mark EWD – Graphite Piston Ring
a.
The Mark EWD graphite piston ring is in two
pieces and can be easily removed.
b.
The new graphite piston ring is supplied as a
complete ring and must be broken into
two equal portions. Do this by placing the ring
horizontally in a vise and applying pres
sure until the ring snaps. Alternately, place
the ring on the edge of s smooth hard surface
and strike squarely with a hammer.
c.
When installing the ring in the valve plug groove,
be sure to match the broken ends of the ring.
Mark EWT Seal Ring – Without Spring Loading
a.
This is a closed ring which must be pried or cut
from the groove and therefore cannot be reused.
After the seal ring is removed, the elastomeric
back-up ring can be slightly spread and
removed.
b.
When installing a seal ring without spring load
ing, apply lubricant to the back-up ring and the
seal ring (Keys 48 and 51). Install the back-up
ring over the stem (Key 30) and fit into
the groove.
c.
Place the seal ring over the top of the valve plug
(Key 25) so it enters the groove on one side of
the valve plug. Gently nudge the seal
ring over the top of the valve plug. Allow time
for the TFE material to cold-flow during
the procedure, so avoid jerking on the ring.
The ring may soom loose when first in the
groove, but will contract shortly after placement
in
the
cage.
Mark EWT – Spring Loaded Seal Ring
a.
When used with valve plugs having a port
diameter of 5-3/8 inches (136.5mm) or less,
the spring loaded seal ring may be removed
without damage by first extracting the retaining
ring (Key 47) with a screwdriver. Slowly slide
the metal back-up ring (Key 51) and seal ring
(Key 48) off of the valve plug (Key 25).
b.
When used with valve plugs having a port diam
eter of 7-inches (178 mm) or greater, the spring
loaded seal ring must be pried or cut from its
groove and cannot be reinstalled.
c.
The spring loaded seal ring must be placed so
that the open side faces the top or bottom of
the valve plug, according to the flow direction
(Figure 3, View A).
M
ark
EW S
EriES
G
lobE
S
tylE
C
ontrol
V
alVES
