Flowserve V-378 R1 Edward Equiwedge Gate Valve - Manual (Page 11)

11
Flow Control Division
Edward Valves
should be blended into the contour of
the casting.
4. Stress relieving is generally recommend-
ed. Decisions to not stress relieve should
factor in piping code rules. The temper-
atures must be based on material speci-
fication and piping code recommenda-
tions. Again, since temperatures are
much higher than those experienced in
welding, there are also disadvantages
that must be considered. Distortion may
result in more damaging problems.
Lower temperature postweld heat treat-
ment is sometimes an option for carbon
steels.
5. The final weld should receive any need-
ed nondestructive testing. This should
include a visual examination and liquid
penetrant or magnetic particle examina-
tion. Some major weld repairs could
even mandate radiography to ensure a
sound weld.
Body Guide Repairs
The body guide grooves guide the gate
through about 95% of the valve stroke and
allow only 5% of the valve stroke to thrust
against the seating surfaces. It is important
that the side faces of the groove be smooth
and free of gouges and burrs. A flat file
can be used to remove any burrs and
raised edges.
Seat Repairs
The seats in a gate valve may require
repair when the seating surfaces allow
fluid to pass. This may be due to erosion
of the surfaces caused by not closing the
valve tightly or seating on foreign material.
Verification of such conditions may be
obtained by a seat blueing test or by close
visual examination.
To correct these conditions seat refinishing
will be necessary. A Dexter gate valve
refinishing fixture will speed up repairs.
See Appendix B for a discussion on use of
the Dexter equipment.
Gate Repairs
Gate repairs to the seating surface can be
done on a flat cast iron lapping plate. The
lapping plate should be large enough so
that the seating surface contacts the full
diameter with sufficient additional surface
allowing the gate to be pushed at least
1/3 of its diameter in any direction.
Clover compound “A”, Norton 320 mixed
with olive or sperm oil, or for rough lap-
ping, Carborundum H20 may be used.
See illustration No. 6A.
Gate guide repairs can be done by rub-
bing the surface with a square steel block
wrapped with emery cloth.
Bonnet Repairs
The valve bonnet provides several functions
as follows: closure of the pressure vessel, a
packing chamber to seal the stem, a back-
seat area sealed with the stem so the valve
can be repacked under pressure, and a
sealing arrangement to prevent leakage to
the atmosphere.
Equiwedge gate valves with metal pressure
seal gaskets have a number of different
angles machined on the bonnet to accom-
modate the pressure seal gasket. These
angles are shown in illustration No. 6B.
Repair Procedures
(cont.)
Illustration No. 6A
Valve Gate on
Lapping Plate
A°
±0.25° 30°
Pressure Seal Bonnet Angles
(Valves with metal gasket only)
Illustration No. 6B
Class 600 Class 900 Class 1500 Class 2500
A
25° +0.5° 35° +0.5° 35° +0.5° 45° +0.5°
- 0.0° - 0.0° - 0.0° - 0.0°