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Packing Used Specially for Valves (801), Patent Product |
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Series of Carbonized Fiber Packing with Graphite (802), Patent Product |
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Series of PTFE packing (827,831,830,808F, 833,835,836)
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Packing Used Specially
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Other Products (864,809,808G)
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Equipments and Materials (We can provide the same trade
with all sorts of materials and equipments for special purpose.) |
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801
Packing Used Specially for Valves |
1. Present Situation for Valves with High Temperature
and
Pressure To valves used in petrochemical and thermal electricity
etc. with high service temperature and high service pressure
(service temperature ≥500℃, service pressure ≥10 MPa), now the
following materials are employed generally for sealing valve
stem.
1.1 The flexible graphite packing ring or braided packing The
flexible graphite thread is the direct raw material used in
making graphite packing. It is one of the most temp-resisting
materials applied to various kinds of sealing materials. It
hasfine self-lubricity (the coefficient of friction is 0.15),
and it still has the lubricity even if used in high temperature
(when temperature is 500℃,the coefficient of friction ≤0.4)
,and its allowable linear velocity may attain 40m/s. It has
good chemical stability and strong corrosion resistance. It
will not be brittle, aged and metamorphic to be used in the
mediums including acid, alkali, salt, organic solvent, steam,
hot oil, grease etc., of which the scope of pH is from 0 to
14.When used in above mediums it is of better sealing effectiveness
with 75% of compressibility and 60% of resilience. And it also
has better impermeability and fine thermal conductivity. But
the flexible graphite products have deadly weakness as follow.
When used in oxidizing medium, the allowable service temperature
and service pressure will reduce to about 50% of the normal
value. Thus it may cause the service condition to be restricted
seriously.
1.1.2 Even if used in non-oxidizing medium, the amount of loss
of temperature at 500℃ has
reached up 8% , so its service life may be cut short greatly
and the pressure variation will
be decreased. Thus it will lead to leakage.
1.1.3 Its mechanical strength is so low that to be broken while
filling. Also its tensile
strength is lower so that to be difficult to clean the packing
case while replacing packing.
2.The Design Principle and Main Parameter of the Packing Used
Specially for Valves
Beginning from 1970s, our country has imported several 300,000-ton-
class ethylene
devices from abroad one after another, of which the service
temperature of power boiler
and splitting boiler surpasses 500℃ and service pressure surpasses
10MPa. The sealing
for their valve stems was a difficult problem to have to be
settled urgently all the time. The
main cause is that there is no a sort of thread, which is able
to reach such service condition
, used for packing.
2.1 Manufacturing Principle, Technology and Structure
The fiber, of which the length is up to 4~10mm, used specially
for diaphragm cloth is employed.
And no subsidiary cotton and other fibers are added as spinning
when 3 yarns are twisted
together. Add high-temp-resisting nickel wire. After thread
is formed, coat homogeneously a
layer of high-temp-resisting lubricating solvent (0.05~0.2mm)
on surface of the thread with
special technology. In this way, then the product is finished
after the thread was braided
and shaped using feed-through braiding machine with 24 spindles
or jacketed braiding machine
made in Japan.
2.2 Properties and Characteristics
Because of that the long fiber chosen to use specially for diaphragm
cloth and high-temp-
resisting nickel wire are twisted
closely together, this material has fine tensile strength up
to 30.1Mpa(See the test report
given by Qingdao Construction Engineering Institute) and its
service pressure can attain
18Mpa.Besides, because of that every kind of material chosen
touse have not more than
2% of heating loss at 600℃, it also has the excellent high-temp-resisting
property.
As the high-temp-resisting lubricating layer was coated, it
still has excellent self-lubricating
property (the coefficient of friction is only 0.2,and the mass
of friction is only 0.04g).
It has the rational structure with 28% of the compressibility
and 27% of resilience; it can
be conformed completely to the packing requirements for compressibility
and resilience.
This material was passed the examination given by Sealing Supervising
and Examining Center
, National Mechanical Industrial Ministry and Examining Center
of Qingdao Construction
Engineering Institute on November 18, 1997. The relative physical
and chemical indexes as
follow.
Density
(g/cm3) |
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Allowable Service Pressure (MPa)
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Needed Tight Force of Packing Gland
(MPa)
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Tensile Strength of Thread Used Specially
for Packing (MPa)
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1.4~1.7 |
0.12 |
18 |
25 |
30.1 |
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Allowable Service Temp (℃)
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Fracture Extensibility of Thread Used
Specially for Packing (%)
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28 |
0.04 |
≤600 |
2 |
15 |
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Through 500 times reciprocating motion of the valve stem with
18MPa of pressure and 600℃
of temperature, the packing has been passed normally by
the above data. So the following
conclusions may be come to.
2.2.1 Because of that high-temp-resisting lubricating layer
was coated on the surface of
every thread, the packing has still fine lubricity at 600℃.
Thus no surface destroy was
occurred during the 500 times simulated reciprocating motion
of valve stem. While in actual
use, a valve is only switched 2~50 times a year, that is,
the packing can be used continuously
over ten years.
2.2.2 A
s the sulfur content of the material chosen to use was controlled
strictly, there is no corrosion
of packing to the valve stem and packing case.
2.2.3 Scope of Application: Sealing for valve stems with high
temperature and high pressure,
which the medium is water vapor and various oils etc..
2.2.4 The allowable max service temperature is 600℃ and the
allowable max service pressure
is 18MPa.
2.2.5 After first filling, the pressure stress should be adjusted
according to the load until to conform
the requirements of sealing.
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