Technical field The invention relates to the technical field of sliding valves, and in particular to a soft seal encapsulated valve member for a sliding valve, i.e. a sliding valve member that is encapsulated by a soft seal material, such as rubber.

Background

Sliding valves may be used in pipeline systems for distributing and/or handling fluids such as water, sewages, natural gas, or similar liquid or gaseous media. A sliding valve comprises a housing defining a passage way for the fluid to flow in an axial direction through the housing. The passage way may be closed by sliding a valve member, also referred to as wedge, into the valve opening in a direction transverse to the axial direction. A transverse plane may be defined as the plane of the transverse movement of the valve member. Typically, the plane of the sliding movement of the valve member is essentially perpendicular to the axial direction. However, a sliding movement in a transverse plane that is inclined with respect to the axial direction, i.e. where the plane in which the valve member moves is not perpendicular to the axial direction, may also be conceived. The valve member of a sliding valve is typically moved in a linear displacement in a first transverse direction. However, instead of a linear translational movement, the sliding valve member may be also be moved in and out of the passage way by a rotational movement around an axis perpendicular to the plane of the sliding movement, wherein the valve member is hinged at a point outside of the valve opening of the passage way. The motion of the valve member is actuated by actuation means. The actuation means may comprise a threaded valve stem configured to act upon a valve nut to produce a linear translational movement for sliding the valve member in or out of the passage way in a first transverse direction parallel to the valve stem. Advan- tageously, in this case, the valve nut may be integrated in the valve member. However, other types of actuation means, comprising lever actuators, gear transmissions, rack and pinion drives, hydraulic means, and/or pneumatic means, may also be conceived.

Under operation, the valve member is subject to considerable pressures in the axial di- rection. In order to take up these axial pressures, guide means may be provided defining a guided path for the displacement of the valve member. The guide means may be a sliding bearing that comprises guide members arranged on lateral portions of the valve member and cooperating guide rails provided on the inside walls of the valve housing, lateral of the passage way. The guide rail is shaped complementary to the shape of the guide member so as to provide guidance at least in an axial direction for a sliding displacement of the valve member in the transverse plane. Preferably, the interaction between guide means and guide rail(s) also provides guidance in a transverse direction perpendicular to the valve member's path.

In a sliding valve of the soft-sealing type, a seal is provided by a soft sealing element, typically made of rubber, which engages a cooperating valve seat, which e.g. may be a dedicated valve seat element or simply a wall of the valve housing. Typically, the soft sealing element is provided on the valve member, wherein a valve member may be formed by a core that is encapsulated by the soft sealing material. The material of the core, for example cast iron, may be prone to degradation/corrosion when exposed to a fluid passed through the valve. The soft sealing encapsulation is therefore provided for purposes of improved corrosion protection of the core. In order to provide an extensive corrosion protection, also the guide members may be covered with the soft sealing material. The problem of such a solution is that the soft sealing material typically is not wear resistant with respect to a sliding motion. Furthermore, typical soft sealing materi- als have a high friction coefficient with respect to most surfaces, in particular if the application of any lubricant is to be avoided for hygienic reasons or for reasons of keeping the level of maintenance to a minimum. This problem may be solved by using slide shoes arranged on the guide members, wherein the slide shoes are preferably made of a wear resistant and corrosion resistant material providing a low friction sliding inter- face with a sliding surface of a cooperating guide rail.

EP 0171693 discloses a sliding valve with a valve member comprising guide members that are attached to a valve member core and moulded together with a rubber encapsulation of the valve member. This solution implicitly limits the choice of slide shoe ma- terials to materials that can be vulcanised together with the soft seal material and can withstand the high temperatures occurring when moulding the soft seal material onto the valve core. A further draw-back is that it may be challenging to keep the soft seal material from contaminating the sliding surface of the slide shoe during the moulding process, thus requiring an additional cleaning and polishing step after de-moulding of the encapsulated valve member. EP 0926410 discloses a sliding valve member, wherein a slide shoe is attached onto guide members after the soft sealing encapsulation has been moulded. The problem with this solution is that the slide shoe is supported by a soft layer preventing a precise control over the valve member movement, in particular under large axial pressures on the valve member resulting in an excessive wear of the valve actuation mechanism as well as the sealing surfaces. Furthermore, when applying a soft seal encapsulation to a valve member, the valve member core is typically engaged by centring pins in order to centre it in the mould. These centring pins leave openings in the soft seal encapsulation thus requiring a subsequent sealing step for these openings. Merely concealing the openings under a loosely attached slide shoe only insufficiently seals these openings and enhances the risk of corrosion.

US 4629160 corresponding to DE 3345133 discloses a valve member for a sliding valve comprising a metal core encapsulated in a rubber elastic material. The metal core is provided with lateral guiding grooves, each having a bottom and two lateral walls. A U-shaped sliding shoe of plastic material is arranged in each guiding groove so that a gap or hollow space is formed between the sliding shoes and the guiding grooves in the metal core. The gap or hollow space is filled with the moulding mass of the rubber elastic jacket encapsulating the metal core. The outer surface of sliding shoes facing the metal core is embedded in the rubber elastic material.

The sliding shoes are supported by the soft rubber elastic material preventing a precise control over the valve member movement, especially under large axial pressures on the valve member.

DE 201 19964 U1 discloses a valve member for a sliding valve comprising a rubber coated core having lateral uncoated guide projection. Each of the projections is provided with a U-shaped jacket or slide shoe being adhesively connected thereto. The U- shaped jackets or slide shoes are adapted to slide in guide grooves in the housing of the valve. A problem with the above valve member is that it is a major challenge to prevent the rubber forming the rubber coating from contaminating the sliding surfaces of the jackets or slide shoes during the moulding process. As a result an additional cleaning process is required. Disclosure of the invention

The object of the present invention is to overcome at least some of the above mentioned draw-backs.

According to one aspect, the object is achieved by a valve member according to claim 1 , wherein advantageous embodiments are recited in the dependent claims referring directly or indirectly to claim 1. According to a further aspect of the invention, the object is achieved by a method of providing a soft seal encapsulated valve member according to claim 1 1 and the dependent claims referring to it.

According to one embodiment, a valve member for a sliding valve comprises a core encapsulated with a soft seal encapsulation and one or more lateral guide members, each guide member being adapted to engage a cooperating guide rail provided inside a housing of the sliding valve so as to take up an axial pressure P exerted on the valve member during operation, wherein the guide members are at least partially covered by a wear-resistant and/or corrosion-resistant slide shoe having a sliding surface adapted for interacting with a corresponding sliding surface of the guide rail, wherein the guide member comprises a prefabricated spacer element of a corrosion-resistant material be- tween the core material and the slide shoe, said prefabricated spacer element being fixedly connected and/or vulcanized together with the soft seal encapsulation of the valve member, so as to be in sealing engagement therewith.

A prefabricated spacer element provided on the guide member facilitates production of the valve member by centring the valve member core in the mould during moulding of the soft seal encapsulation onto the core. The spacer element has to be made of a material that is compatible with the thermal conditions, to which it necessarily is subjected during the moulding step. The spacer material should preferably also be corrosion resistant when exposed to a fluid passed through the valve. The spacer material should furthermore be suited for being vulcanized/fixedly sealed together with the soft seal material of the encapsulation. Thereby, a sealed corrosion resistant encapsulation of the core is achieved, protecting the core from the exposure to any corrosive fluid. The sliding surface of each of the guide members is formed by a slide shoe attached to the exterior of the spacer element. The slide shoe is adapted so as to provide, in combina- tion with a corresponding sliding surface of the guide rail, a wear resistant low friction bearing. Preferably, the spacer element is attached directly to the core and configured to support the slide shoe, thereby improving the precision of guiding/controlling the movement of the valve member.

Further, according to one embodiment of a valve member, the spacer element is made of a material with a relatively large elastic modulus as compared to the soft seal encapsulation material. By selecting a spacer material that is relatively stiff as compared to the soft seal encapsulation material, the stability of the slide shoe attachment is improved, and the precision of the valve member operation is increased. This is particularly advantageous when moving the valve member under a significant one-sided pres- sure load due to a pressure drop across the valve. Thereby, an enhanced durability and reliability of the valve member and of a sliding valve comprising such a valve member is achieved.

Examples of suitable soft seal encapsulation materials are rubber materials, such as EPDM rubber or nitrile rubber (NBR). Preferred slide shoe materials comprise plastic materials, such as polyoxymethylene (POM). For example, a plastic slide shoe glides well on a guide rail surface that is covered with an epoxy coating. However, corrosion resistant metals, such as brass or stainless steel, or ceramic materials may also be used, but require suitable wear-resistant low-friction surfaces on the cooperating guide rails. The spacer can be made from a plastic material that is thermally stable at temperatures of the moulding process. Alternatively, the spacer may also be made of a hard elastomer material or a corrosion resistant metal, such as brass or stainless steel.

Further, according to one embodiment of a valve member, the spacer element is at- tached to the core by snap-fit engagement. A snap-fit engagement simplifies the installation of the spacer element and thereby facilitates a low cost production.

Further, according to one embodiment of a valve member, the spacer element is formed as a clamp with an essentially U-shaped cross-section, wherein the legs of the U-shape are provided with inwardly projecting lugs engaging a mating recess provided on the core. The U-shape provides an advantageous snap-fit clamp, which is easy to attach on projecting ears of the valve member core and facilitates centred mounting of the valve member core in a tool for moulding the soft seal encapsulation. By attaching a clamp that embraces the valve member core in between the two legs of the U-shape, the outside surfaces of the U-clamp spacer may easily be engaged in between opposite mould parts of the moulding tool in the closed position thereof. The spacer element may be formed of a plastic material, preferably a thermoplastic material. It should however be noted that the spacer element may also be made of a thermosetting material.

Further, according to one embodiment of a valve member, the valve member comprises two guide members arranged in a lateral direction on opposing portions of the periphery of the valve member. Preferably, a first guide member is arranged on the periphery of the valve member projecting in a first lateral direction parallel to the trans- verse plane, and a second guide member is arranged on an opposing portion of the periphery of the valve member projecting in a second lateral direction parallel to the transverse plane. The term Opposing' may be defined with respect to a central axis parallel to the direction of linear displacement of the valve member in the transverse plane. In a valve stem actuated sliding valve, the central axis may coincide with the longitudinal axis of the valve stem. Preferably, the guide members are arranged symmetrically with respect to the central axis and more preferably symmetrical with respect to a mirror plane comprising both the central axis and the axial direction. Thereby, it is achieved, that an axial pressure acting on the valve member under operation is taken up and distributed symmetrically to guiding means on both sides of the valve housing.

Further, according to one embodiment of a valve member, the core is made of metal, preferably cast iron. A metal core provides the valve member with sufficient stiffness/strength to satisfy strict requirements for withstanding pressures that may occur under operational conditions. A metal core made of cast iron may be adapted to satisfy these operational requirements while keeping production cost low.

According to a further aspect of the invention, a sliding valve comprises a valve member according to any of the above-mentioned embodiments. Thereby, the reliability and durability of the valve is increased.

According to a further embodiment, the spacer element is in direct contact with the core or an adhesive primer applied thereto. Thereby the spacer element is directly supported by the core so as to provide a firm support for the slide shoe. According to an embodiment, the spacer element is in direct contact with the slide shoe. Thereby the slide shoe is directly supported by the spacer element, so as to provide a firm and solid support for the slide shoe.

A further aspect of the invention relates to a method of producing a soft seal encapsulated sliding valve member comprising one or more guide members, each guide member being adapted to engage a cooperating guide rail provided on the inside of a sliding valve housing so as to take up an axial pressure P exerted on the valve member during operation. The method comprises the steps of

Providing a core having one or more lateral projections,

Applying one or more prefabricated spacer elements of a corrosion-resistant material to the one or more lateral projections,

Moulding a soft seal encapsulation onto the core using a mould, said mould engaging in a closed position thereof the one or more prefabricated spacer elements so as to centre the core in the mould cavity, the soft seal encapsulation being sealed to the core and to the one or more spacer elements so as to provide a fluid tight encapsulation of the core, and

Covering the encapsulated lateral projection at least partially with a wear resistant and/or corrosion resistant slide shoe.

By the method, a sliding valve member according to any of the above-mentioned embodiments can be produced. The valve member is adapted for use in a sliding valve, wherein the valve may be opened or closed for a fluid to flow through a passage way defined by a housing of the valve by means of the valve member. When the valve member is in its closed position, the passage way defined by the valve housing is blocked. The soft seal material seals the interface between the sliding valve member and its cooperating valve seat. The valve member may be moved between an open position and a closed position by sliding it in a transverse direction in or out of the pas- sage way. In order to cope with the substantial one-sided pressures that may occur under operational conditions, the sliding valve member movement is guided by means of guide members provided on lateral portions of the valve member. The guide members cooperate with complementary guide rails arranged lateral of the passage way on the inside of the valve housing to form a sliding bearing. A core of the valve member is made of a material that may be prone to corrosion when exposed to a fluid passing through the valve. The core is protected against corrosion by encapsulating it with a soft sealing material, the sealing material being a thermoplastic or thermosetting material such as rubber. The encapsulation may be formed in a thermoplastic or thermosetting moulding process, wherein the core is placed inside a moulding tool and supported by centring means so as to allow the encapsulating soft seal material to flow around and cover the valve member core. Prior to placing the core in the mould, spacer members of a thermally resistant material are attached to the lateral projections of the core. When closing the mould around the core, the mould parts of the mould engage the spacer members, so as to support the core from the lateral projections in a centred position in the mould. Additional centring means may be provided to engage the valve member core at uncritical peripheral positions, e.g. where the encapsulation has an opening for inserting/attaching actuation means, such as a valve stem opening giving access to a valve nut integrated in the valve member core. The encapsulation is then formed in a moulding step, such as an injection moulding process, wherein the soft sealing material is sealed/vulcanized together with the spacer element, thereby providing a fluid tight encapsulation of the core material and thus an efficiently corrosion protection of the core. The guide members may at least partially be covered by slide shoes. The inside of the slide shoes engages the exterior surface of the spacer member, and the spacer member is attached to the core. The sliding surface of the slide shoe is adapted so as to provide, in combination with a corresponding sliding surface of the guide rail, a wear- resistant low-friction sliding bearing.

Further, according to one embodiment of a method for producing a sliding valve member, the moulding step further comprises shaping the outer surface of the spacer element by plastic deformation so as to form an engaging surface for holding the slide shoe. The deformation may take place during closing of the mould. By pressing the op- posing mould part surfaces engaging the spacer element during the moulding of the soft seal encapsulation towards each other, the outside surface of the spacer element may be shaped to comply with pre-defined dimensions matching the dimensions of a pre-formed slide-shoe. Thereby, a reliable production process is achieved. The spacer element may be formed of a plastic material, preferably a thermoplastic material. An adhesive primer may be applied to the spacer element in order to provide a reliably connection to the encapsulation. Further, according to one embodiment of a method for producing a sliding valve member, the slide shoe is attached to the guide member by friction fit and/or snap-fit. The slide shoe is adapted to provide a rapid engagement with the guide member, thereby facilitating a simple and low cost production of the valve member. Brief Description of the Drawings

In the following, the invention is further explained referring to an exemplifying embodiment. The drawings show on Fig. 1 a front elevational view of a sliding valve, partially cut away,

Fig. 2 a top elevational view of the sliding valve of Fig. 1 with the valve bonnet removed, Fig. 3 a perspective view of a valve core and a spacer element,

Fig. 4, a perspective view of a soft seal encapsulated valve member with slide shoes, Fig. 5 and Fig. 6 cross-sectional views of details of the valve member.

Detailed description of the Invention

Referring to Fig. 1 and Fig. 2, a sliding valve 1 has a housing 2 defining a passage way 3 for a fluid to flow through the housing 2 in an axial direction A. The housing has flanges 4, 5 for installing the valve in a pipeline system (not shown) for liquid or gaseous media. The housing further comprises a top flange 6 for attaching a valve bonnet 7 holding a valve box 8 through which a stem 9 passes from the outside of the valve 1 to the inside. Rotating the stem 9 around its longitudinal axis actuates a valve member 10 by engaging a valve member nut 1 1 , which is attached to a stem sided portion of the valve member 10, to move in a first transverse direction T1 parallel to the stem 9. The movement of the valve member 10 is guided by guiding means comprising guide rails 12 interacting with guide members 20 to form a sliding bearing for a linear transla- tional movement of the valve member 10 in the first transverse direction T1. The guide rails 12 are essentially parallel to the first transverse direction T1 , and are arranged on the inside of the housing 2 and lateral of the passage way 3. Two guide members 20 are provided on the periphery of valve member 10 projecting in an outward direction from opposing lateral portions of the valve member as seen in a second transverse direction T2 essentially perpendicular to the first transverse plane T1. Together, the first and second transverse directions T1 , T2 span a transverse plane T, which is essential- ly perpendicular to the axial direction A. By sliding the valve member 10 oriented in the transverse plane T to a closed position blocking the passage way 3 and to an open position retracted from the passage way 3, the sliding valve 1 may be closed and opened, respectively. The valve member 10 comprises a valve member core 13 made of cast iron encapsulated by a soft sealing material 21 , such as rubber. The guide members 20 are formed as lateral projections 17 of the core 13. Each projection 17 carries a prefabricated spacer element 22, which together with the soft sealing material 21 holds a slide shoe 23, e.g. means of a friction-fit engagement, snap-fit, glue, or any other suitable means of attachment. The slide shoes 23 are configured to run in the guide rails 12 to provide a corrosion resistant, wear-resistant and low-friction sliding bearing for the movement of the valve member 10. The soft seal material 21 provides a soft seal between the valve member 10 and the housing 2 when the valve member 10 is in its closed position, thereby providing a fluid tight closure of the passage way 3. The fluids that are passed through the valve 1 which may be any of the liquid or gaseous media handled/distributed in the pipeline system where the valve is to be used, may be corrosive to the cast iron core 13. Therefore, the soft seal material 21 covers the core 13 to provide a corrosion protection by preventing exposure of the core 13 to the fluids. Producing a valve member comprises the step of providing a valve member core 13, which, for example, may be produced of cast iron. Fig. 3 shows a perspective view of a valve member core 13 adapted for use in a sliding valve 1 as shown for example in Figs. 1 and 2. The core 13 comprises a main body 14 with a centrally arranged bore 15. The bore 15 is configured to receive a valve stem 9, wherein a longitudinal axis of the bore 15 essentially coincides with the longitudinal axis of the stem 9 extending in a first transverse direction T1. In a top portion, the bore 15 comprises a cavity 16 for holding the valve member nut 1 1. The core 13 further comprises laterally arranged projections 17 for forming the guide members 20. The projections 17 project outwardly in opposite directions parallel to a second transverse direction T2, essentially mirror symmetrically to the first transverse direction T1 in a transverse plane T spanned by the first and second directions T1 , T2. In a next step, a spacer element 22 with an essentially U-shaped cross-section with a pair of legs with lugs 24 is attached to the core 13 by snap-fit engagement of lugs 24 of the spacer element 22 to a complementary recess 18 on the projections 17. Furthermore, a block 19 for forming the valve member nut 1 1 is mounted into the cavity 16. The thus prepared valve member core 13 is then engaged by the mould parts of a moulding tool (not shown), wherein the core 13 is centred inside the mould by supporting it from the prefabricated spacer elements 22, and preferably by further clamping the wedge nut block 19 with cooperating centring pins in the first transverse direction T1 from the top, and through bore 15 from the bottom. In a further step, a soft seal material 21 , such as rubber, is moulded onto the valve core 13 and fixedly connected and/or vulcanized together with the spacer element 22 and with the wedge nut block 19, so as to form a fully sealed corrosion-resistant encapsulation of the cast iron core 13. Engaging the core 13 via the spacer elements 22 and the block 19 avoids direct openings to the cast iron surface that otherwise would remain after the moulding process when engaging the core 13 directly with centring pins. In the process according to the invention, openings in the soft seal encapsulation 21 , resulting from supporting/centring the core 13 in the mould, are preferably covered by a corrosion resistant material.

The spacer element 22 is made of a corrosion free or at least corrosion resistant mate- rial, which is suited to withstand typical process conditions that may occur during moulding of a soft sealing material 21 , such as rubber. Furthermore, the material of the spacer element 22 should be suited for being fixedly connected and/or vulcanized together with the soft seal material 21 in a sealing connection. In order to provide a reliable and durable sealing connection between the core and/or the spacer element and between the spacer element and the encapsulation, the spacer element may be primed with an adhesive agent before being arranged in the core and the core arranged in the mould. Furthermore, the block 19 is preferably made of a corrosion free or at least corrosion-resistant and wear-resistant material. Also the block 19 should withstand typical process conditions that may occur during moulding of the soft sealing material 21 and should be suited for being vulcanized together with the soft seal material 21 in a sealing connection. The valve member nut 11 is formed from the block 19 by cutting an in- ner thread in a central bore in the block 19 in the longitudinal direction of the bore 15. Preferably, the inner thread of valve member nut 11 is cut after the soft seal moulding step. The inner thread of the valve member nut 11 mates with a thread on the cooperating valve stem 9. A typical example for a material for the valve member nut is brass.

An almost finished valve member 10, apart from cutting the inner thread of the valve member nut, is shown in Fig. 4. The valve member 10 is encapsulated with a soft seal material 21 that is fixedly connected and/or vulcanized together with the block 19 and the spacer elements 22, so as to form a fully sealed corrosion resistant encapsulation of the core. The guide members are covered by slide shoes 23.

Details of the guide member construction are shown in the cross-sectional views of Figs. 5 and 6. Notably, referring to Fig. 5, also the inner wall of the central valve stem bore 15 is coated with the soft seal material 21. The valve nut 1 1 is mounted in the cav- ity 16 and fixedly connected and/or vulcanized together with the soft seal encapsulation 21. Furthermore, the spacer element 22 is clamped to the core 13 in a recess 18 on the projection 17 and likewise fixedly connected and/or vulcanized together with the soft seal encapsulation 21. The outside of the guide member 20 is formed by a slide shoe 23 that is fixed to the spacer member 22 and the soft seal encapsulation 21 , preferably by a friction-fit engagement.

The soft seal encapsulation material is selected for its capability of deforming easily to provide a soft seal at the interface between the valve member and the valve housing, rather than for providing a stiff support to a slide shoe. Therefore, generally the spacer element 22 is preferably made of a material that is relatively rigid as compared to the soft seal encapsulation 21. Thereby, the slide shoe 23 is supported more precisely than what could be achieved in the absence of the spacer element 22. Consequently, the precision of the movement of the valve member 10 in guide rails 12 of a sliding valve 1 is increased, and the operation of the sliding valve 1 is improved.

Fig. 6 shows a detail of the guide member 20 as seen in a cross-section along line VI- VI as indicated in Fig. 5. The spacer element 22 is located between the guide member 23 and the core 13, and provides a rigid support through a direct mechanical connection of the guide member 23 to the core 13. The spacer element 22 is clamped to the core 13 by a snap fit engagement. The spacer element 22 has an essentially U-shaped cross-section, wherein the legs of the spacer element 22 are provided with lugs 24 engaging a complementary recess 18 provided on a lateral projection 17 of the core 13.

Reference Numbers

1 Sliding valve

2 Housing

3 Passage way

4, 5 Flange

6 Top flange

7 Valve bonnet

8 Valve box

9 Stem

10 Valve member

1 1 Valve member nut

12 Guide rail

13 Core

14 Main body

15 Bore

16 Cavity

17 Projection

18 Recess

19 Block

20 Guide member

21 Encapsulation

22 Prefabricated spacer element

23 Slide shoe

24 Lug

A Axial direction

T1 , T2 Transverse directions