Flowserve V-378 R1 Edward Equiwedge Gate Valve - Manual (Page 12)

12
Flow Control Division
Edward Valves
Repair Procedures
(cont.)
If the gasket sealing surface of the bonnet
has been damaged by corrosion, erosion
or careless handling, this surface can be
machined in a lathe. Chuck the bonnet,
indicate true the large diameter and the
bottom face before cutting the angle. The
angle should be generated using a high
speed or carbide cutting tool. Remove as
little stock as possible to clean up. The
surface finish should be held to 63 micro
inch (1.6 micrometer) or better.
Backseat
The backseating surface is inlaid with
hardfacing. Any machining on this surface
must be done with carbide tools. The
included angle of the backseat is 60° and
the tolerance on the half angle is ± 0.25°.
The surface finish should be held to 63
micro inch (1.6 micrometer) or better.
Machining of this surface can be done in
the same setup as machining the pressure
seal angle. Once again the angle should
be generated using a carbide cutting tool.
Porosity in Bonnet
In most gate valve sizes and pressure class-
es, the bonnet is made from a steel cast-
ing. Steel castings are subject to various
types of defects such as shrinkage or
porosity. Weld repair any defect in the
bonnet wall the same as a body. If exten-
sive repairs are required, remachining of
the packing chamber, backseat, and pres-
sure seal angle may be required because
of distortion of these surfaces.
Stem Repairs
The basic function of a valve stem is to
actuate the valve open or closed. Because
it penetrates a pressure boundary, it must
provide a diameter for the packing to seal
leakage to the atmosphere and provide a
seal in the fully open or backseated posi-
tion so that packing may be replaced
under pressure. Stems are made of high
quality martensitic stainless steel or other
stainless alloy and hardened to withstand
the high stresses. Welding is not recom-
mended. Only cosmetic repairs to the
packing diameter and machining of the
backseat should be attempted. The angle
on the backseat of the stem is 28° – 0.50°
+ 0.25°. First contact is made at the top of
the conical surface. Valve stems must be
concentric and free from score marks on
the packing diameter and backseat area to
perform the functions listed above. When
a stem is bent or deeply scored on the
packing diameter, it should be replaced.
Field Repair Equipment
Available from the Edward Valves plant at
Raleigh, North Carolina are some basic
tools for repairing valves in the field. This
equipment was developed for customer use
on a rental basis. Contact your local
Edward Valves sales representative for
more information. A partial list of this
equipment follows:
1. Four sizes of Dexter seat refinishing
machines complete with refinishing plates
for valve sizes 2-1/2 thru 28.
(See Appendix B, pg. 30)
2. Two sizes of portable boring machines
capable of reboring the pressure seal
area in body on valves size 10 and larg-
er. (See Appendix B, pg. 30)