STUFFING BOX FOR A VALVE

PRESSE-ETOUPE POUR UNE SOUPAPE

English Abstract

The invention relates to
a valve that contains a piston (2) linked
with the valve body (8) and received in
a housing (4), and a stuffing box (14)
interposed between the piston (2) and the
housing (4). The stuffing boxes of valves
used for media having a high melting point
and being operated close to the melting
point risk being damaged by so-called
freezing medium due to the adhesive
properties of the medium in temperature
ranges below the melting point. The aim
of the invention is therefore to improve
such a valve with few constructive efforts
in such a manner that the material of the
stuffing box reliably works in the liquid
range of the medium. To this end, the
housing (4) is provided with a heating
device (16) in the area of the stuffing box
(14). The axial length of said heating
device is larger than the axial length of
the stuffing box (14), and the heating
device (16) axially protrudes beyond an
axial end (22) of the stuffing box (14) by
a predetermined length (24, 28).

French Abstract

L'invention concerne une soupape contenant un piston (2) relié à un corps de soupape (8) et logé dans une enveloppe (4), ainsi qu'un presse-étoupe (14) situé entre le piston (2) et l'enveloppe (4). Dans les soupapes destinées à un milieu présentant un point de fusion élevé et lorsqu'on opère à proximité du point de fusion, il existe un risque d'endommagement du presse-étoupe par le milieu qui </= gèle >/= , en raison des propriétés adhésives du milieu dans des plages de températures inférieures au moins de fusion. L'invention vise donc à développer la soupape tout en maintenant une dépense de conception faible afin que le matériau du presse-étoupe opère de manière sûre dans la plage liquide du milieu. A cet effet, l'enveloppe (4) comprend, dans la zone du presse-étoupe (14), un dispositif de chauffage (16) dont la longueur axiale est supérieure à la longueur axiale du presse-étoupe (14) et qui dépasse axialement au moins une extrémité axiale (22) du presse-étoupe (14) sur une longueur prédéfinie (24, 28).

Claims

8
Claims
1. A valve comprising a piston connected with a valve body and supported in a
housing, and a packing or a packed seal arranged between said piston and said
housing,
wherein the housing is provided in the area of the packing or the packed seal
with a
heating device having an axial length is greater than that of the packing or
the packed
seal, and wherein said heating device protrudes axially beyond at least one
axial end of
the packing or the packed seal by a predetermined length.
2. A valve according to claim 1, wherein the housing in which the packed seal
is
received is greater in length than the packed seal by a predetermined amount.
3. A valve according to claim 1, wherein a pressure ring associated with the
packed
seal and surrounding the piston axially protrudes with one end into the area
of the heating
device.
4. A valve according to claim 1, wherein the heating device comprises a
heating
jacket which surrounds the housing and which forms a gap through which a heat
transfer
medium can flow.
5. A valve according to claim 4, wherein the heating jacket is connected with
the
housing.
6. A valve according to claim 5, wherein the heating jacket is connected with
a
mounting flange of the housing.
7. A valve according to claim 5, wherein the heating jacket is connected to
the
housing by a weld seam.
8. A valve according to claim 1, further comprising a seal support bushing
having
tolerances in the range of 0.01 mm to 0.2 mm relative to at least one of the
piston and the
housing.
9. A valve according to claim 8, wherein said tolerances are about 0.05 mm.

9
10. A valve according to claim 8, wherein the support bushing has thermal
expansion
characteristics substantially equal to at least one of the piston and the
housing.
11. A valve according to claim 8, wherein the support bushing at least at
surfaces
bounding at least one of the piston and the housing, has a greater surface
hardness than
one of the piston and the housing.
12. A valve according to claim 1, wherein a pressure ring or a packing
pressure sleeve
associated with the packing or the packed seal has tolerances relative to the
housing in the
range of 0.05 to 0.2 mm.
13. A valve according to claim 12, wherein the pressure ring or packing
pressure
sleeve has tolerances relative to the housing of about 0.08 mm.
14. A valve according to claim 1, wherein a pressure ring or packing pressure
sleeve
associated with the packing or the packed seal has tolerances relative to the
piston in the
range of 0.05 to 0.4 mm.
15. A valve according to claim 14, wherein said pressure ring or packing
pressure
sleeve has tolerances relative to the piston of about 0.1 mm.
16. A valve according to claim 14, wherein the pressure ring or the packing
sleeve is
provided with at least one relief groove along its exterior.
17. A valve according to claim 16, wherein the pressure ring or packing sleeve
is
provided with up to 8 relief grooves.
18. A valve according to claim 17, wherein the pressure ring or packing sleeve
is
provided with from 2 to 4 relief grooves.
19. A valve according to claim 16, wherein said relief grooves are axial
grooves.
20. A valve according to claim 14, wherein a side of the pressure ring or the
packing
pressure sleeve facing away from the packed seal is provided with at least one
substantially radial service groove.

21. A valve according to claim 20, wherein the pressure ring or packing
pressure
sleeve is provided with from 2 to 6 substantially radial service grooves.
22. A valve according to claim 21, wherein the pressure ring or packing
pressure
sleeve is provided with from 2 to 4 substantially radial service grooves.
23. A valve according to claim 1, wherein one of the housing is provided with
exterior
insulation in the area of at least one of the packed seal and the heating
device.
24. A valve according to claim 23, wherein said insulation is also provided
surrounding the working chamber of the piston.

Description

. . ,
WO 01/79735 PCT/EP01/03963
STUFFING BOX FOR A VALVE
The invention relates to a valve with a stuffing box seal in
accordance with the features set forth in the preamble of Claim 1.
US Patent 4,886,241 describes such a valve with a stuffing box
seal, which is arranged between the housing and the piston connected
with the housing and axially displaceable or rotatable within the
housing. In valves for media with a high melting point, which operate
near the melting point, there is a risk of damaging the stuffing box
due to "freezing" of the medium as a result of the adhesive properties
of the medium in temperature ranges below the melting point. In
principle, these problems can be counteracted by heating the housing,
but the complexity required therefor has thus far been quite
considerably.
Based thereon, the object of the invention is to configure the
valve with low design complexity in such a way that the stuffing box
material works reliably within the liquid range of the medium and/or
the stuffing box material is protected from the freezing point. The
temperature of the stuffing box should very reliably remain in the
CONFIRMATION COPY
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liquid range above the melting point of the medium flowing through the
valve despite the simple construction.
This object is attained by the features set forth in Claim 1.
The proposed valve with a stuffing box seal is distinguished by
its functionally reliable construction and ensures with high
reliability that the temperature of the stuffing box is always within
the liquid range above the melting point of the medium. In the area of
the stuffing box, the housing comprises a heating device whose axial
length is greater by a predefined amount than the length of the
stuffing box. The heating device protrudes over the stuffing box in a
predefined area with at least one end, advantageously with both ends.
Advantageously, the heating device protrudes over the stuffing box end
along an area of 30 to 60 mm. The heating device advantageously
comprises a heating jacket surrounding the housing along the exterior.
A gap for a heating medium, particularly a heatable fluid, is provided
between the housing and the heating jacket. Alternatively, within the
scope of the invention, the heating device can comprise tubes through
which a heating medium flows, or an electrical heating coil or the
like, which are arranged especially on the exterior surface of the
housing in the area of the stuffing box.
Furthermore, in the area of the stuffing box and a bearing
bushing adjacent to the stuffing box, the piston is advantageously
designed to have a constant diameter, where no recesses, annular
collars or the like are present. Particularly advantageously, the
bearing bushing which is provided for piston guidance is designed with
very tight tolerances relative to the housing on the one hand and the
piston on the other hand. This is particularly important for sensitive
media, which are subject to change as a function of temperature and/or
retention time, especially since the selected tolerance affects the
quality of sensitive media. In view of the tolerances necessary for the
required quality of the medium, the material of the bearing bushing
according to the invention has at least approximately the same thermal
expansion characteristics as the material of the housing and/or the
piston. In addition, the piston guide is advantageously substantially
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WO 01/79735 3 PCT/SP01/03963
harder than the housing and/or the piston material in order to prevent
"corrosion." Within the scope of the invention, said tolerances are
preferably in the range of 0.01 mm to 0.2 mm, preferably in the range
of 0.05 mm.
Further developments and special embodiments of the invention are
set forth in the dependent claims and in the following description of a
special embodiment, which is provided by way of example.
The drawing shows a portion of the valve in an axial cutting
plane, namely in the area where a piston 2 passes through a housing 4,
which comprises a mounting flange 6. Piston 2 and a valve body 8 that
is connected therewith and that is configured, for instance, as a
shut-off valve and/or a control valve, are axially displaceable or
rotatable about a longitudinal axis 10. A bearing bushing 12 is
provided between the cylindrical inner surface of housing 4 and the
outer surface of piston 2. Axially adjacent to the bearing bushing 12,
a stuffing box 14 or a stuffing box packing with a plurality of sealing
rings is provided. Piston 2 has a constant outside diameter in axial
direction at least in the area of stuffing box 14, preferably also in
the area of bearing bushing 12. The material of the stuffing box or its
rings is selected taking into account the thermal and mechanical load.
The stuffing box is configured in such a way that sliding and
strength-imparting sealing materials are combined. Depending on the
temperatures to be controlled by the valve, sealing materials with
and/or without fabric insert may be used. Through the number of the
sealing rings, an adaptation to the pressure to be controlled by the
valve is effected. The piston guide or bearing bushing 12 is
manufactured with very tight tolerances relative to piston 2 on the one
hand and in housing 4 on the other hand. These tolerances, in
particular, are in the range of 0.01 mm to 0.2 mm and preferably in the
range of 0.05 mm. Moreover, the material of the bearing bushing 12 has
substantially the same thermal expansion -characteristics as the
material of piston 2 and/or housing 4.
According to the invention, housing 4, which receives bearing
bushing 12 and stuffing box 4, has a substantial axial length and is
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WO 01/79735 4 PCT/SP01/03963
provided with a heating device 16. Heating device 16 advantageously
comprises a heating jacket, which according to the invention surrounds
the long housing 4. As may be seen, an especially annular gap 18,
through which a heatable medium flows, is present between the
preferably cylindrical heating device and the heating jacket 16. The
stuffing box 14 has an axial length 20. Particularly advantageously the
heating device 16 has a substantially greater axial length than the
stuffing box 14 and protrudes at least over one end, in the drawing
over the right stuffing box end 22 by a defined length 24, which
preferably ranges between 30 and 60 mm. The heating device 16 also
protrudes over the second stuffing box end 26 by a defined length 28.
According to the invention the temperature of the heating device or the
heating medium in gap 18 is defined such that the temperature of the
stuffing box is reliably within the liquid range of the medium flowing
through the valve. Particularly advantageously the heating jacket 16
with its end 30 associated with valve body 8 is connected with mounting
flange 6 of housing 4 by a weld seam 32. As may be seen, gap 18 is
therefore also substantially longer than stuffing box 14 whose
temperature is thus always reliably within the liquid range above the
melting point of the medium.
Between stuffing box 14 - also referred to as a packing - and a
pressure sleeve 34 or a packing pressure sleeve, a pressure
distribution ring 36 is arranged to ensure uniform transfer of the
pressure from the pressure sleeve to the packing. The pressure sleeve
or pressure ring 34, at its end facing toward the stuffing box 14,
comprises at least one radial relief bore 38 through which any liquid
medium flowing out of the stuffing box is guided to the outside of
pressure ring 34, where premature freezing of the medium is prevented
by the action of the heating device. Although the relatively large or
long piston 2 removes a lot of heat, there is thus no risk that the
medium will freeze along the outer circumference of the pressure ring
34 due to the heating device. The stuffing box or packing 14 is
compressed by means of pressure sleeve 34, and the necessary initial
tension is applied to ensure the seal of the system.
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According to the invention, pressure sleeve 34 axially extends
far enough into the heated area and/or the heating device 22 that
cooling of the stuffing box 14 is avoided. As may be seen, pressure
sleeve 34 with its end facing toward stuffing box 14 extends into the
heated area by a defined length 24 as explained above. Since heat loss
is to a significant extent caused by the piston of the valve, end 40 of
pressure sleeve 34, which protrudes into the area of the heating
device, is particularly important in maintaining the liquid state of
the medium. It should be noted here that the durability of the stuffing
box packing depends on the liquid state to a significant extent.
Advantageously, tolerances relative to the housing side on the one hand
and the piston on the other hand are therefor defined for pressure
sleeve 34. The tolerances relative to the housing side range from
0.05 mm to 0.2 mm and are preferably on the order of magnitude of
0.08 mm to ensure the supply of heat. The tolerances between pressure
sleeve 34 and piston 2 must ensure mobility on the one hand and take
into account heat removal via piston 2 one the other hand. They range
between 0.05 and 0.4 mm, and are preferably on the order of magnitude
of 0.1 mm.
Furthermore, especially axial relief grooves 42 are preferably
provided on the outside of pressure sleeve 34 to remove the medium in
axial direction. The number of these longitudinal grooves 42 is defined
between 1 and 8, preferably between 2 and 4. Since the grooves
interfere with the heat transport of heating device 16 their number
should be minimized. In addition, radial service grooves 44 are
provided on the pressure-flange-side of pressure sleeve 34 and are used
to monitor stuffing box packing 14 and/or to engage with a tool. By
means of the last groove it can be decided whether to tighten or
replace the packing. The radial service grooves are particularly
important for the detachability of the pressure sleeve 34. The number
of the radial grooves 44 is, in particular, 2 to 6, preferably 2 to 4.
To avoid any undesirable heat removal, a heat seal 48 is provided
between pressure sleeve 34 and a pressure plate 46.
An insulation 50 surrounding the valve housing at least in the
area of piston 2 is preferably provided to prevent heat removal. In
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WO 01/79735 6 PCT/EP01/03963
order to avoid that the heat removal via piston 2, pressure sleeve or
pressure ring 34 and a rod assembly of a gear (not depicted) causes the
medium in the stuffing box to freeze, the working chamber of piston 2
is advantageously also surrounded by insulation 50. This makes it
possible to reduce the freezing range of the medium far enough that it
cannot have a negative influence on the driving forces.
In addition, a piston protection element 52 is provided to
prevent contamination on the one hand and minimize heat losses on the
other. To that extent care must be taken during manufacture to avoid a
chimney effect. In addition, piston protection element 52 is configured
in such a way that the moving part is protected against the medium
draining from the stuffing box. The piston protection element is
furthermore configured in such a way that the through-flowing portion
of the medium can drain in downward direction. Moreover, piston
protection element 52 protects against contact, so that nobody can get
pinched in the movable part. Finally, a medium outlet 54 is provided,
which points downwardly from the area of stuffing box 14. It should be
noted that when the valve is installed, the longitudinal axis 10
extends substantially vertically and medium outlet 54 is below stuffing
box 14. This downwardly directed medium outlet 54 prevents
contamination of the part of insulation 50 that is located below it.
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.. , = - =
WO 01/79735 7 PCT/LPO1/03963
Reference Numerals
2 piston
4 housing
6 mounting flange
8 valve body
longitudinal axis
12 bearing bushing
14 stuffing box
16 heating device / heating jacket
18 gap
length of 14
22 first stuffing box end
24 predefined length of 16
26 second stuffing box end
28 predefined length of 16
end of 16
32 weld seam
34 pressure sleeve / pressure ring
36 pressure distributor ring
38 relief bore
end of 34
42 relief groove
44 radial service groove
46 pressure plate
48 heat seal
insulation
52 piston protection element
54 medium outlet
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Representative Drawing