a-Capsulated body seals:
As the body seal is located in a complete isolated cavity (capsule), it is far away from the fire , i.e. it is not affected directly by the fire so it can keep its physical shape and hence its function for a considerable period.
b-
Metal-to-metal sealing:
Even if the body seal is destroyed by the fire, MV valve can keep the fluid inside it with no external leakage. This is because of the wide metal-to-metal sealing surface between the body and the end as those contact surfaces are of a high level finishing.
c- High quality assembly fasteners:
Also the body is assembled to the end by a ASTM A 193 Gr B7 studs (Gr B8 for stainless steel valves), and ASTM A 1934 Gr 2H nuts (Gr 8 for stainless steel valves). This adds rigidity to the assembled valve to withstand in the fire conditions.
d- Anti-blow out stem:
The anti-blow out stem insures that the stem will never blow out from the valve and no external leakage because of the metal-to-metal sealing between the stem flange and the body.
MV
features no internal leakage at fire accident due to the presence
of a second metallic seats on which the ball sits
after the damage of the Teflon seats thus cutting the flow
and prevent internal leakage.
The
design of the stem shape, and its insertion from inside the
body, prevent the stem to blowout by the pressure within the
body cavity and allow the replacement of the stem packing
while the valve is at ON position and the fluid inside it
is at line pressure.
The
anti static device is a pair of a small 303 stainless
steel ball on a loaded spring installed in the stem to insures
a constant connection between the stem and the ball, and between
the stem and the body. This structure insures a continuous
discharging of the electrostatic charges.
Stem
packing set is composed of base packing, intermediate
packing set and, top packing. The stem packing set is
compressed by the flange and the gland flange. This packing
set, the gland, the gland flange are assembled by a couple of
studs and nuts. This structure allows to compensate for the
operational wear simply by retightening the nuts.
