Patent Description:
Microfibrillated cellulose ("MFC", also known as "reticulated" cellulose or as "superfine" cellulose, or as "cellulose nanofibrils", among others) is described, for example, in <CIT>.

MFC may be manufactured by processing, in particular compressing and subsequently expanding through one or more orifices. Therein, cellulose pulp may be periodically delivered or pumped through a check valve blocking back-flow against a conveying direction, respectively.

In accordance with the present invention, the check valve is for blocking back flow of fluid though a passage, wherein said fluid comprises cellulose, wherein said fluid preferablyis pressurized with a peak pressure of at least <NUM> bar while the check valve is closed.

<CIT> refers to a variable displacement vane pump including a relief valve which includes a valve bore, a spherical valve element in the valve bore, a valve seat fixed onto one axial side of the valve bore and having a through hole and an annular seat surface on which the valve element is seated when the relief valve is in a closed position, a coil spring disposed on the other axial side of the valve bore, and a valve element retainer disposed between the valve element and the coil spring, wherein the seat surface is configured such that when the relief valve is in the closed position, a center of the valve element is located offset from a central axis of one winding seating portion of the coil spring which is disposed on an opposite side of the seat surface, in a radial direction of the valve bore.

<CIT> refers to a check valve for a fuel pump, including: a seat face formed on a fuel passage; a valve member that includes a ball made of ceramics and is adapted to approach and leave the seat face; and a spring for biasing the ball toward the seat face, wherein the fuel passage is closed when the ball is seated on the seat face, and the fuel passage is opened when the ball is brought apart from the seat face by a pressure generated against the biasing force of the spring, wherein the ball seating portion of the seat face is formed into a curved face having a larger curvature than that of the ball, so that the ball and the seat face come into a band-shaped contact at the seating time.

<CIT> refers to a valve in which the combination of a T shaped union or casing provided with a central passage and vertical transverse passsages communicating therewith in the central and vertical transverse arms of said casing, said arms being provided with valve chambers and each valve chamber having in the lower part thereof a circular sharp edge valve seat and each chamber having in the upper part thereof a plurality of circumferentially spaced checking and alining devices and a globular metallic valve vertically reciprocal in each chamber and adapted to cooperate with said valve seats and said alining ribs for the purpose designated. This valve can be used as check valve in any piping system, especially for pumping semi-fluid and fibrous substances such as wood or paper pulp. The aim is to avoid clogging of the valve by the material in the pump.

<CIT> refers to a pressure control valve has a non-uniformly tapered valve bore that has an increasing diameter as it extends downstream, wherein an interface angle defined in part between a valve ball and the valve bore in the area of the smallest gap between them, increases as the valve ball is increasingly displaced away from a valve seat of the valve bore.

It is an object of the present invention to improve an apparatus for processing cellulose pulp comprising at least one check valve, to improve a method for processing cellulose pulp wherein cellulose pulp periodically flows through at least one check valve, or to improve, preferably intermittently, blocking back-flow of fluid respectively.

According to one aspect of the present invention, one object outlined above is solved by use(age) of a check valve according to claim <NUM>. Claims <NUM>, <NUM> refer to an apparatus for processing cellulose pulp comprising at least one check valve as described herein, and a method for processing cellulose pulp wherein cellulose pulp periodically flows through at least one check valve as described herein, respectively. As already emphasized, such use of the check valve establishes particular advantageous applications of the present invention.

According to one aspect of the present invention, a check valve comprises a housing which partially or fully contains a valve seat and a valve member, which according to one embodiment of the present invention are inserted into said housing.

According to one embodiment of the present invention, the valve seat is or has been inserted after the valve member, i.e. the valve member is or has been inserted first and the valve seat is or has been then placed onto the inserted valve member respectively. This sequence improves assembly and/or stability of the check valve.

The housing may be a one-part housing - which in particular may improve fluid tightness - or a multiple-part housing - which in particular may simplify manufacturing and/or assembly.

Additionally or alternatively, said valve seat is axis-symmetrical and/or manufactured (in) one-piece according to one embodiment of the present invention, which, in particular, may improve fluid tightness and/or weight and/or simplify manufacturing and/or assembly.

Additionally or alternatively, said valve member is axis-symmetrical and/or manufactured (in) one-piece according to one embodiment of the present invention which in particular may improve fluid tightness and/or weight and/or simplify manufacturing and/or assembly.

According to one aspect of the present invention, the valve member comprises a, preferably continuous, contact surface which is convex(ly) curved and is denoted as member contact surface herein. According to one embodiment of the present invention said member contact surface is an at least essentially spherical surface, preferably a spherical surface.

Said member contact surface may, in particular, improve sealing performance of the check valve.

According to one aspect of the present invention, the valve seat comprises a (fluid) passage through which fluid flows, preferably periodically, in a conveying direction or which is adapted thereto or used therefor respectively. Said passage may be a single-line or multi-line passage and/or (defined by) an inner bore.

According to one aspect of the present invention, the valve seat comprises a, preferably continuous, (counter-)contact surface which is denoted as seat contact surface herein. Said seat contact surface is axis-symmetrical according to one embodiment of the present invention, preferably axis-symmetrical to a longitudinal and/or symmetry axis of the inner bore and/or vale seat. Such a seat contact surface preferably improves sealing performance of the check valve.

According to one aspect of the present invention, the valve member or its member contact surface respectively is pretensioned against the valve seat or its seat contact surface respectively and seals said passage when or by contacting it, or is adapted thereto or used therefor respectively.

The valve member can be moved or is moveable against said pretension or increasing said pretension respectively, thereby opening said passage for fluid flow, preferably self-acting or autonomously respectively due to a (fluid) pressure difference upstream versus downstream of the check valve or is adapted thereto or used therefor respectively.

By selecting or varying the pretension, accordingly, an opening pressure (difference) at which the check valve opens self-actingly may be set advantageously according to one embodiment of the present invention. According to a preferred embodiment, such opening pressure (difference) is at least <NUM> bar, preferably at least <NUM> bar, more preferably at least <NUM> bar, and/or at most <NUM> bar, preferably at most <NUM> bar, more preferably at most <NUM> bar, the pretension being selected accordingly.

According to one aspect of the present invention, said passage has a minimal flow-through area or minimal opening or orifice respectively of at least <NUM><NUM>, preferably of at least <NUM><NUM>, and/or preferably has a minimal inner diameter of at least <NUM>, preferably a minimal inner diameter of at least of at least <NUM>.

According to one embodiment of the present invention, the minimal flow-through area of the passage or seat valve respectively is at most <NUM><NUM>, preferably at most <NUM><NUM>, further preferably at most <NUM><NUM>, more preferably at most <NUM><NUM>, even more preferably at most <NUM><NUM>, and/or the passage has a minimal inner diameter of at most <NUM>, preferably a minimal inner diameter of at most <NUM>, further preferably a minimal inner diameter of at most <NUM>, more preferably a minimal inner diameter of at most <NUM>, even more preferably a minimal inner diameter of at most <NUM>. The present invention performs particularly advantageously within such range or at such relatively large minimal flow-through areas respectively.

According to one aspect of the present invention, the seat contact surface has a concave curvature wherein a, preferably minimal, maximal, average and/or constant, curvature radius of said concave curvature is larger than a, preferably minimal, maximal, average and/or constant, curvature radius of the convex member contact surface.

According to one embodiment of the present invention, such concave curvature with such a larger curvature radius is believed to significantly improve the sealing performance and/or durability of the check valve, in particular when used with fluids which are high(er) pressurized and/or comprise solids. Without wishing to be bound by theory, it is assumed that such geometry provides a particularly advantageous elastic deformation and therefore stress distribution within valve seat and valve member.

According to one embodiment of the present invention, said curvature radius of the seat contact surface is at least <NUM>%, preferably at least <NUM>%, of said curvature radius of the member contact surface and at most <NUM>%, preferably at most <NUM>%, of said curvature radius of the member contact surface.

Selecting the ratio between said two curvature radii of the seat and member contact surface respectively has surprisingly been found to advantageously (further) improve the sealing performance and/or durability of the check valve.

According to one embodiment of the present invention, the seat contact surface comprises, preferably is, a radius, preferably a machined and/or constant radius, which is at least <NUM>%, preferably at least <NUM>%, of a/the (constant) radius of the spherical member contact surface, and at most <NUM>%, preferably at most <NUM>%, of the (constant) radius of the spherical member contact surface.

Thus, if in a preferred embodiment, the spherical member contact surface has a radius of <NUM>, preferably the valve member being a ball with a diameter of <NUM>, then the seat contact surface may preferably comprise or be a radius of at least <NUM> (= <NUM>·<NUM>), preferably at least <NUM> (= <NUM>·<NUM>), and at most <NUM> (= <NUM>·<NUM>), preferably at most <NUM> (= <NUM>·<NUM>), most preferably between <NUM> and <NUM>. If the member contact surface's radius or ball diameter is chosen differently, the radius of the seat contact surface is preferably scaled accordingly.

Selecting the ratio between said (machined and/or constant) radius of the seat contact surface and the (constant) radius of the (spherical) member contact surface, respectively, has surprisingly been found to advantageously (further) improve the sealing performance and/or durability of the check valve.

According to one embodiment of the present invention, an axial length of said (machined and/or constant) radius, measured preferably along a longitudinal axis of the valve seat, preferably a symmetry axis of the valve seat or seat contact surface respectively, is at least <NUM>,<NUM>%, preferably at least <NUM>%, of said radius and at most <NUM>%, preferably at most <NUM>,<NUM>%, of said radius.

Thus, if for example the seat contact surface comprises, preferably is, a radius of <NUM>, then said radius may preferably extend axially at least <NUM> (= <NUM>·<NUM>), preferably at least <NUM> (= <NUM>·<NUM>), and at most <NUM> (= <NUM>·<NUM>), preferably at most <NUM> (= <NUM>·<NUM>), most preferably between <NUM> and <NUM>. If the radius is chosen differently, the axial length may preferably be scaled accordingly.

Selecting said ratio between said (machined and/or constant) radius of the seat contact surface and is axial length has surprisingly been found to advantageously (further) improve the sealing performance and/or durability of the check valve.

According to one embodiment of the present invention, said radius of the seat contact surface, preferably its center or reference point respectively, is laterally offset (away) from a/the longitudinal axis of the valve seat, preferably a/the symmetry axis of the valve seat or seat contact surface respectively.

According to one embodiment of the present invention, said lateral offset points away from the radius so that, in a preferred embodiment, in a cross-section comprising the longitudinal axis of the valve seat a (lateral) distance between two opposing radii of the seat contact surface becomes smaller.

Additionally or alternatively said lateral offset is at least <NUM>%, preferably at least <NUM>%, and at most <NUM>%, preferably at most <NUM>%, of said radius of the seat contact surface according to one embodiment of the present invention.

Thus, if in a preferred embodiment the seat contact surface has or is a radius of <NUM> then said radius may preferably be lateral offset by at least <NUM> (= <NUM>·<NUM>), preferably at least <NUM> (= <NUM>·<NUM>), and at most <NUM> (= <NUM>·<NUM>), preferably at most <NUM> (= <NUM>·<NUM>), most preferably between <NUM> and <NUM>. If the radius is chosen differently, the lateral offset may preferably be scaled accordingly.

Surprisingly, it has been found that a concave curvature seat contact surface which is fully or partially defined or established respectively by a (machined and/or constant) radius which is laterally offset, preferably with a ratio between lateral offset and radius as given above, may significantly (further) improve the sealing performance and/or durability of the check valve.

According to one embodiment of the present invention, the (machined and/or constant) radius of the seat contact surface, preferably its center or reference point respectively, is axially outwards offset (away) from a, preferably seat-sided, front face of the valve seat along its longitudinal axis. If not denoted otherwise, the terms "axial(ly)" and "radially" herein are used with respect to the longitudinal axis, preferably symmetric axis, of the check valve or valve seat or seat contact surface respectively.

Thus, "axially" refers to a direction parallel to the longitudinal axis, "radially" to a direction perpendicular to the longitudinal axis and intersecting the longitudinal axis.

Said axial offset is at least <NUM>%, preferably at least <NUM>%, and at most <NUM>%, preferably at most <NUM>%, of said radius of the seat contact surface according to one embodiment of the present invention.

Thus, if in a preferred embodiment the seat contact surface has a radius of <NUM>, then said radius may preferably be axially offset by at least <NUM> (= <NUM>·<NUM>), preferably at least <NUM> (= <NUM>·<NUM>), and at most <NUM> (= <NUM>·<NUM>), preferably at most <NUM> (= <NUM>·<NUM>), most preferably between <NUM> and <NUM>. If the radius is chosen differently, the axial offset may preferably be scaled accordingly.

Surprisingly, it has been found that a ratio between axial offset and radius as given above may significantly (further) improve the sealing performance and/or durability of the check valve.

According to one embodiment of the present invention, a transition between the seat contact surface, preferably the/its (machined and/or constant) radius, and a, preferably valve member-sided, front face of the valve seat and/or a transition between the seat contact surface, preferably the/its (machined and/or constant) radius, and an/the inner bore of the passage (each) comprises, preferably is, a (transition) radius, preferably a machined and/or constant radius, respectively which preferably is at most <NUM>%, preferably at most <NUM>%, of the radius of the seat contact surface.

Thus, if in a preferred embodiment, the seat contact surface has a radius of <NUM> then said transition radius/radii may preferably (each) be at most <NUM> (= <NUM>·<NUM>), preferably at most <NUM> (= <NUM>. If the seat contact surface's radius is chosen differently, the transition radius/radii may preferably be scaled accordingly.

By such transition radii the fluid dynamics may be improved advantageously according to one embodiment.

As already pointed out, the valve member preferably may comprise, preferably be, a ball. Thus the check valve may preferably be a so-called ball design check valve according to one embodiment of the present invention.

In accordance with the present invention, the valve member is guided linearly within the housing, preferably by a poppet, according to one embodiment of the present invention.

Said ball and poppet may be independent parts - which may in particular improve manufacturing and/or sealing and/or guiding performance - or be connected or formed integrally with one another respectively (so-called integrated poppet and ball design check valve) which in particular may improve assembly and/or weight.

According to one embodiment of the present invention, the poppet may have an angular cross-section, preferably a hexagonal cross-section, which may (further) improve guidance. Additionally or alternatively, the poppet may comprise a lateral outer surface which contacts or slides along respectively a corresponding guiding surface of the housing so as to guide the valve member or poppet respectively linearly within the housing according to one embodiment of the present invention, which may (further) improve guidance. Additionally or alternatively, the poppet may comprise one or more inner channel(s) transferring fluid from the valve seat passage if the check valve (is) open(s) or the inner channel(s) being adapted thereto respectively according to one embodiment of the present invention which may (further) improve guidance.

Additionally or alternatively, the valve member may be pretensioned by one or more springs, preferably coil spring(s), according to one embodiment of the present invention. Such valve members can, preferably by combining two or more of said features, (further) improve the sealing performance and/or durability of the check valve.

According to one embodiment of the present invention, the housing is made from, preferably, but not limited to, stainless steel in various grades and conditions. The stainless steel may, or may not, be heat treated, coated, sintered and/or untreated.

The valve seat is made from ceramic or steel, preferably stainless steel, according to one embodiment of the present invention. The stainless steel may be heat treated, coated, sintered and/or untreated.

Additionally or alternatively, the valve member is sintered and/or made from diamond, ruby or ceramic or steel according to one embodiment of the present invention. According to one embodiment of the present invention, the valve member is made from steel, preferably stainless steel in various grades and conditions. The stainless steel may be heat treated, coated, sintered and/or untreated.

Additionally, or alternatively, the poppet and/or (coil) spring(s) can be made from, but not limited to, preferably, stainless steel in various grades and conditions. The stainless steel may, or may not, be heat treated, coated, sintered and/or untreated.

According to one embodiment of the present invention, the seat contact surface is surface hardened and/or coated.

Such material selection or treatment, respectively, can, preferably in combination, (further) improve the sealing performance and/or durability of the check valve.

According to one embodiment of the present invention, the valve seat inserted into a cavity within the housing comprises a collar, said collar preferably being an axial(ly protruding) collar and/or comprising the seat contact surface and/or being inserted, preferably form-fittingly, into a corresponding inner bore of the housing. According to one embodiment of the present invention, said collar, in particular its (ending) ledge, may define an axial position of the valve seat within the housing, in particular by abutment. Additionally or alternatively, the collar may fix a radial position of the valve seat within the housing, in particular by form-fit, according to one embodiment of the present invention.

An axial length of said collar, measured preferably along a/the longitudinal axis of the valve seat, is at least <NUM>%, preferably at least <NUM>%, and at most <NUM>%, preferably at most <NUM>%, of said curvature radius of the member contact surface according to one embodiment of the present invention.

Thus, if in a preferred embodiment the spherical member contact surface has a radius of <NUM>, preferably the valve member being a ball with a diameter of <NUM>, then such axial collar length may preferably be at least <NUM> (= <NUM>·<NUM>), preferably at least <NUM> (= <NUM>·<NUM>), and at most <NUM> (= <NUM>), preferably at most <NUM> (= <NUM>·<NUM>), most preferably between <NUM> and <NUM>. If the member contact surface's radius is chosen differently, the axial collar length may preferably be scaled accordingly.

Selecting the axial collar length accordingly may particularly advantageously distribute stress from the seat contact surface into the valve seat or its collar respectively.

The collar may be a radially inner collar and/or protrude (axially) towards the valve member according to one embodiment of the present invention. Thus, the valve seat may comprise a base and the collar protruding (axially) from an axial surface of said base towards the valve member so that said axial surface establishes an ending ledge of the collar, wherein base and collar are manufactured (in) one-piece and/or base and/or collar have a circular cross-section and/or the collar has a smaller, in particular maximal, (outer) circumferential length then the base and/or said, preferably radially outer, axial surface of the base or ending ledge of the collar respectively abuts, preferably axially, against the housing and/or limits an axial displacement of the valve seat within the housing towards the valve member according to one embodiment of the present invention. According to one embodiment of the present invention, the valve seat has a stepped outer lateral surface which preferably may be defined at least in part by the (preferably wider) base and the (preferably smaller, radially inner) collar.

Such (axial) collar, in particular support of the radially inner collar by form-fit with the housing, in particular its inner bore, and/or limiting an axial displacement of the valve seat within the housing towards the valve member by the collar's ending ledge, may advantageously improve assembly of the check valve and/or stress distribution within the valve seat and/or sealing performance between valve member and valve seat.

Additionally or alternatively, the valve seat inserted into a/the cavity within the housing is held in place by a gland defining, in particular comprising, an inlet opening, in particular port, of the check valve according to one embodiment of the present invention. According to one embodiment of the present invention said gland is made from steel, preferably stainless steel. The stainless steel may be heat treated, coated, sintered and/or untreated.

According to one embodiment of the present invention housing and gland are different elements and/or gland and valve member are located at (axially) opposite sides of the valve seat.

This can advantageously improve assembly and/or reduce the weight and/or size of the check valve according to one embodiment.

According to one embodiment of the present invention, the gland extends (axially) into the housing. Additionally or alternatively, the gland presses the valve seat against the housing, preferably in the direction towards the valve member, according to one embodiment of the present invention. Additionally or alternatively, the gland comprises a, preferably external, thread engaging with a, preferably internal, thread of the housing according to one embodiment of the present invention.

Such gland may particularly advantageously (further) improve assembly of the check valve and/or sealing between valve seat and housing, preferably allowing to adjust pretension between valve seat and housing and thus sealing between them.

According to one embodiment of the present invention, the curvature radius of the member contact surface is at least <NUM> and at most <NUM>. Thus, if the valve member comprises, preferably is, a ball, said ball may have a diameter of at least <NUM> and at most <NUM>.

Additionally or alternatively, a diameter of the valve member ball is at least <NUM>% and at most <NUM>% of a minimal diameter of the passage, wherein said diameter of the passage may in particular be a minimal hydraulic diameter of the passage. A minimal hydraulic diameter dh,min is defined as usual by the quotient of the fourfold minimal flow-through area Amin of the passage divided by its circumference U: dh,min = (<NUM>·Amin)/U. Thus, if the minimal flow-through area of the passage has a circular shape, said hydraulic diameter corresponds to the diameter of said circle (dh,min = (<NUM>·Amin)/U = [<NUM>·(d/<NUM>)<NUM>·π]/(d·π) = d). The minimal flow-through area of the passage is preferably (defined as) the smallest or minimal free cross-sectional area of the passage through which fluid (can) flow(s). Thus, according to a preferred embodiment, a fluid flow through the passage is limited or defined by said minimal flow-through area times (mean) fluid velocity times density of the fluid respectively.

So, if the passage is defined by an inner bore having a minimal circular cross-section with a diameter of <NUM> and the valve member comprises, preferably is, a ball, then a diameter of said ball preferably is at least <NUM> (= <NUM>·<NUM>) and at most <NUM> (= <NUM>·<NUM>), most preferably between <NUM> and <NUM>. If the passage's diameter is chosen differently, the ball diameter may preferably be scaled accordingly. Thus, if the passage's diameter is <NUM>, the ball diameter may preferably be at least <NUM> (= <NUM>·<NUM>) and at most <NUM> (= <NUM>·<NUM>), most preferably between <NUM> and <NUM>.

Such sizing has been found to provide advantageous sealing performance and/or durability of the check valve.

According to one aspect of the present invention, the check valve as described herein is used for automized blocking return-flow or back-flow respectively of fluid through the passage, wherein said fluid comprises solids, preferably cellulose, and/or is pressurized with a maximal pressure of at least <NUM> bar, preferably at least <NUM> bar, further preferably at least <NUM> bar, more preferably at least <NUM>,<NUM> bar, even more preferably at least <NUM> bar, most preferably at least <NUM>,<NUM> bar, while the check valve is closed or blocks back-flow of said pressurized fluid respectively and/or flows through the open passage with a maximal flow rate of at least <NUM> I/min, preferably at least <NUM> I/min, further preferably at least <NUM> I/min, more preferably at least <NUM> I/min. According to one embodiment of the present invention the maximal pressure may be limited by <NUM>,<NUM> bar, preferably <NUM>,<NUM> bar, more preferably <NUM>,<NUM> bar. The maximal flow rate may be limited by <NUM> I/min, preferably <NUM> I/min, further preferably <NUM>/min according to one embodiment of the present invention. So, according to one embodiment of the present invention, the check valve is used or adapted respectively to seal automized against return or back-flow of fluid comprising solids, in particular cellulose, and being pressurized with a maximal pressure of at least <NUM> bar, preferably at least <NUM> bar, further preferably at least <NUM> bar, more preferably at least <NUM>,<NUM> bar, even more preferably at least <NUM> bar, most preferably at least <NUM>,<NUM> bar, respectively.

The check vale is particularly suitable for such (ultra) high-pressure/flow rate and/or solid/cellulose-comprising fluid applications.

Therefore, according to one aspect of the present invention, an apparatus for processing cellulose pulp comprises at least one pulp feed line with one or more check valves as described herein. Additionally or alternatively, according to one aspect of the present invention in a method for processing cellulose pulp, cellulose pulp periodically flows through the passage of one or more check valves as described herein in a conveying direction, said self-acting check valve(s) blocking back-flow through the passage against said conveying direction, in particular during, preferably cyclic, compression of the pulp downstream of the check valve.

In accordance with the present invention, the valve member is guided linearly within the housing.

The invention is described in more detail in the following, with reference to the enclosed figures, which are only meant to be illustrative, wherein:.

<FIG>, <FIG> show a perspective or sectional view of a check valve respectively according to one embodiment of the present invention.

Said check valve comprises a housing (<NUM>) which contains an axis-symmetric valve seat (<NUM>) and a ball (<NUM>) (valve member).

Said valve member or ball (<NUM>), respectively, comprises a spherical and thus convex member contact surface and is guided linearly within the housing by a poppet (<NUM>).

Said valve seat (<NUM>) inserted into a cavity within the housing comprises a collar (<NUM>) and is held in place by a gland (<NUM>) defining an inlet port (<NUM>) of the check valve. The valve seat comprises an inner bore (passage) (<NUM>) (see <FIG>) and a seat contact surface which will be described in further detail with respect to <FIG>.

The ball (<NUM>) and thus its member contact surface is pretensioned by a coil spring (<NUM>) via poppet (<NUM>) against said valve seat (<NUM>) and thus its seat contact surface and seals said passage when sitting on the valve seat (<NUM>) or seat contact surface respectively.

According to embodiments of the present invention, the gland (<NUM>), the coil spring (<NUM>) and/or the poppet (<NUM>) is made from steel, preferably stainless steel. The stainless steel may be heat treated, coated, sintered and/or untreated.

If fluid pressure difference between the inlet port and an outlet opening of housing (<NUM>) exceeds a predetermined threshold, self-acting check valve, in particular its passage (<NUM>), opens by ball (<NUM>) being pushed against said pretension (i.e. to the left in <FIG>), thereby (further) compressing coil spring (<NUM>). As soon as fluid pressure difference drops sufficiently, self-acting check valve, in particular its passage, closes by ball (<NUM>) being pushed against valve seat, in particular its seat contact surface (i.e. to the right in <FIG>).

The circular inner bore or passage (<NUM>) respectively has a (hydraulic) diameter d1 of <NUM>, i.e. a minimal flow-through area of approximately <NUM><NUM> ((<NUM>/<NUM>)<NUM>·π).

The housing (<NUM>) comprises an inner bore with a slightly smaller minimal diameter d2 which opens into an outlet opening of the check valve respectively.

As depicted in <FIG>, the seat contact surface is (defined by) a radius R1 of <NUM>. Accordingly, the ball (<NUM>) may have a diameter of <NUM> according to one embodiment so that the seat contact surface radius R1 = <NUM> is approximately <NUM>% of the spherical valve member contact surface radius of <NUM>/<NUM> = <NUM>, i.e. more than <NUM>% and less than <NUM>% of R1. According to one embodiment the seat contact surface is axis-symmetric with respect to axis A.

Said radius R1 or its center point respectively is axially outwards offset away from a front face (<NUM>) of the valve seat along its longitudinal axis A (to the left in <FIG>) by an axial offset a of approximately <NUM> and laterally offset from the longitudinal axis A by a lateral offset b, wherein said lateral offset b points away from the seat contact surface (downwards in <FIG>) and is approximately <NUM>. c denotes an axial length of collar (<NUM>).

Said laterally and axially offset radius R1 transits into the front face (<NUM>) by a transition radius R2 of approximately <NUM> and into the inner bore of the passage (<NUM>) by a transition radius R3 of approximately <NUM>.

As shown in <FIG>, <FIG>, the valve seat (<NUM>) comprises a base (<NUM>) and the radially inner collar (<NUM>) protruding axially (horizontally in <FIG>, <FIG>) from an axial surface (23A) of said base towards the valve member (<NUM>) (to the left in <FIG>, <FIG>) so that the valve seat has a stepped outer lateral surface and said axial surface (23A) establishes an ending ledge of the collar, wherein base (<NUM>) and collar (<NUM>) are manufactured (in) one-piece, the collar (<NUM>) having a smaller maximal outer circumferential length then the base (<NUM>) and the axial surface (23A) of the base (<NUM>), i.e. ending ledge of the collar (<NUM>), abuts against the housing (<NUM>) and thus limits an axial displacement of the valve seat (<NUM>) within the housing (<NUM>) towards the valve member (<NUM>) (to the left in <FIG>, <FIG>).

The gland (<NUM>) extends into the housing (<NUM>) and comprises an external thread (6A) engaging with an internal thread (1A) of the housing (<NUM>).

For assembly, spring (<NUM>), poppet (<NUM>) and ball (<NUM>) may be inserted into the cavity (1B) of the housing (<NUM>) first, followed by valve seat (<NUM>) and gland (<NUM>) screwed into the housing('s thread) (<NUM>(A)).

The poppet (<NUM>) comprises one or more inner channels (4A) for fluid from the valve seat passage <NUM> (if the check valve (is) open(s)).

<FIG> shows part of an apparatus for processing cellulose pulp according to one embodiment of the present invention, wherein the check valve of <FIG> is positioned at a pulp feed line L for delivering cellulose pulp P.

Claim 1:
Use of a check valve for blocking back flow of fluid (P) through a passage (<NUM>), wherein said fluid comprises cellulose, said fluid preferably being pressurized with a maximal pressure of at least <NUM> bar while the check valve is closed and/or said fluid preferably flowing through the open passage with a maximal flow rate of at least <NUM> I/min;
wherein said check valve comprises
- a housing (<NUM>) which contains:
- a valve seat (<NUM>) comprising the passage (<NUM>) and a seat contact surface (R1), wherein said valve seat is made from steel or a ceramic material; and
- a valve member (<NUM>) comprising a convexly curved, preferably essentially spherical, member contact surface;
said member contact surface being pretensioned against said seat contact surface for sealing said passage;
said valve member being movable increasing said pretension for opening said passage;
wherein
- said passage has a minimal flow-through area of at least <NUM><NUM>; and
- said seat contact surface has a concave curvature wherein a curvature radius of said concave curvature is larger than a curvature radius of the member contact surface, and
- said valve member is guided linearly within the housing.