Note: Descriptions are shown in the official language in which they were submitted.
CA 02246922 1998-09-09
SPLIT KNIFE GATE VALVE HAVING A UNIFORMLY
COMPRESSED AND CONSTRAINED RESILIENT GATE SEAT
AND METHOD FOR PRODUCING THE SAME
Technical Field
The present invention relates to knife gate valves. -
Backp-round of the Invention
Knife gate valves have traditionally been used to control the flow of heavy
slurries transported through tubular conduits. The knife gate has a blade
portion with a
beveled edge to cut through the material suspended in the slurry as the knife
gate is
lowered to seal off the flow through the valve. The knife gate typically
closes against
the metal valve body, and the slurry assists in sealing the valve.
A problem associated with using a knife gate to control the flow of slurries
of
light viscosities is that the material accumulating on the surface of the
valve seat
prevents a tight seal. Therefore, knife gate valves controlling the flow of
light
viscosity slurries typically employ a resilient gate seat liner that is
squeezed between
the knife gate and the metal valve body when the valve is in the closed
position.
When an adhesive slurry (e.g., paper pulp) is being handled, however, the
slurry
material that accumulates on the gate seat liner tends to cause the knife gate
to adhere
to and pull out the seat liner when the knife gate is retracted to open the
valve. The
flowing slurry may then carry the seat liner downstream in the conduit system.
Although lubricating the gate-contacting surface of the valve seat liner can
reduce
surface friction and thereby prevent adhesion of the knife gate to the seat,
the
lubricating fluid may be quickly carried away by moving slurry.
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To avoid this problem, a valve has been introduced
that comprises two, essentially flat, valve body members
bolted together about a resilient gate seat. Each bolt runs
through a bolt hole in the resilient gate seat to positively
retain it. Two principal problems occur with this design.
The first problem arises during operation. The essentially
flat valve body members to not constrain the sealing member
in the radial dimension (defined relative to the center of
the flow opening). As a result, when the valve is closed,
the knife gate pushes the resilient gate seat radially
outwardly. Although the fasteners running through the
sealing member constrain this radial movement, enough
deformation is possible between each pair of fasteners that
the effectiveness of the seal is reduced.
The second problem arises during manufacturing.
If one bolt is fastened more tightly than another, the gate
seat will be compressed more in one spot than in another.
This reduces the effectiveness of the seal. It is even
possible that pressurized slurry could leak around one or
more loosely tightened fasteners. Tightening all the bolts
equally, which is necessary to ensure a good seal, increases
the expense and complicates the manufacturing process.
Summary of the Invention
An object of an embodiment of this invention is to
provide a knife gate valve having a positively retained
resilient gate seat that is physically constrained to
prevent deformation and that thereby produces a better seal.
An advantage of an embodiment of the present
invention is that it provides a knife gate valve that is
easily assembled.
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Another advantage of an embodiment of the present
invention is that it provides a knife gate valve that
requires reduced force to move the knife gate between open
and closed positions.
The knife gate valve of an embodime'nt of the
present invention comprises a set of fasteners, wherein each
fastener extends through a first body member, a U-shaped
resilient gate seat, and a second body member to form a
valve body that is attachable between two conduits to define
a connecting flow passageway. The resilient gate seat is
positively retained by the set of fasteners and includes
along its length a pair of raised ribs that are compressed
against the surfaces of the first and second body members
for improved sealing.
The first body member has a flange around its rim
such that when the two body members are bolted together, the
flange contacts the rim of the second body member. The body
members, when bolted together, define a seat-retaining
recess having a predetermined width and a gate receiving
space for receiving a knife gate. The gate seat, fastened
into place between the body members, is uniformly compressed
along its length to the predetermined width.
The gate seat includes a seating region positioned
adjacent the gate receiving space that includes a raised
contact surface extending along the length of the gate seat.
The width of the raised contact surface is less than the
thickness of the knife gate to reduce friction between the
knife gate and gate seat interface, and thereby reduce the
force required to open and close the knife gate.
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The embodiment of the present invention also
comprises a method of assembling the above-described knife
gate valve by tightening each fastener until the flange of
the first body member meets the rim of the second body
member. The metal-to-metal contact provides a hard stop to
screw rotation, thereby easing the manufacturing process.
According to another embodiment of the invention,
there is provided a knife gate valve for controlling fluid
flow between two aligned conduits, comprising: a first body
member having an outer side to which a conduit is attachable
and an inner side, the first body member having a first flow
opening defining a fluid flow passageway and having a first
rim that includes a first flange extending in a direction
away from the inner side; a second body member having an
outer side to which a conduit is attachable and an inner
side, the second body member having a second flow opening
axially aligned with the first flow opening and having a
second rim, the second body member contacting the first body
member such that the second rim abuts the first flange to
define a recess and a gate receiving space, the recess
having a recess length; a knife gate having a blade portion
that fits within the gate receiving space; a gate actuator
for moving the blade portion of the knife gate along the
recess length to occlude the fluid flow passageway; a
resilient gate seat positioned to conformably fit within the
recess to form an interface between the knife gate and the
first flange, the resilient gate seat having a profile and a
length; and a set of fasteners spaced apart along the length
of the gate seat to collectively fasten together the first
body member, the gate seat, and the second body member so
that the first flange and the second rim contact each other
to cause the recess to hold the resilient gate seat at a
predetermined compression that is uniform along the length
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of the gate seat and so that the first flange constrains
movement of the gate seat to thereby provide a tight fluid
seal.
According to a further embodiment of the
invention, there is provided a method of producing a knife
gate valve for controlling fluid flow between two aligned
conduits, comprising: providing a first body member having a
first outer side to which a conduit is attachable and a
first inner side, the first body member having a first
opening that defines a flow passageway between the conduits
and having a first rim, the first rim including a first
flange extending away from the first inner side and
including multiple first spaced-apart fastener holes;
providing a second body member having a second outer side to
which a conduit is attachable and a second inner side, the
second body member having a second rim that includes
multiple second spaced-apart fastener holes and a second
opening that is axially aligned with the first opening;
providing a resilient gate seat having a length that
includes multiple third spaced-apart fastener holes along
its length; and fastening the first body member to the
second body member about the resilient gate seat by
receiving a fastener in each of corresponding axially
aligned ones of the first, second, and third fastener holes
and securing each fastener, the first flange and the second
body member contacting each other and thereby forming a
recess to hold the resilient gate seat at a predetermined
compression that is uniform along the length of the
resilient gate seat and to constrain movement of the
resilient gate seat to provide a tight fluid seal.
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According to a still further embodiment of the
invention, there is provided a knife gate valve for
controlling fluid flow between two aligned conduits,
comprising: a first body member having an outer side to
which a conduit is attachable and an inner side, the first
body member having a first flow opening defining a fluid
flow passageway; a second body member having an outer side
to which a conduit is attachable and an inner side, the
second body member having a second flow opening axially
aligned with the first flow opening, the second body member
and the first body member together defining a recess and a
gate receiving space, the recess having a recess length; a
knife gate having a blade portion that fits within the gate
receiving space, the blade portion having a thickness; a
gate actuator for moving the blade portion of the knife gate
along the recess length to occlude the fluid flow
passageway; a resilient gate seat positioned to conformably
fit within the recess to form an interface between the knife
gate and the first and second body members, the resilient
gate seat having a profile, a length, and a seating region
along the length, the seating region positioned adjacent the
gate receiving space and including a contact surface for
seating against the blade portion of the knife gate, the
contact surface having a width that is less than the
thickness of the blade portion to reduce friction between
the knife gate and the gate seat; and a set of fasteners
spaced apart along the length of the gate seat to
collectively fasten together the first body member, the gate
seat, and the second body member to provide a tight fluid
seal.
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Additional objects and advantages of this
invention will be apparent from the following detailed
description of preferred embodiments thereof, which proceeds
with reference to the accompanying drawings.
Brief Description of the Drawings
Fig. 1 is a front elevational view of a first
preferred embodiment of the knife gate valve of the present
invention that is shown partly in cross section with the
knife gate in the closed position.
Fig. 2 is a front elevation view of the knife gate
valve of Fig. 1 that is shown with the knife gate in the
closed position.
Fig. 3 is a sectional view taken along lines 3-3
of Fig. 2.
Fig 4 is an enlarged detail cross-sectional view
of the portion of Fig. 3 that is included within circle 4.
Fig. 5 is an exploded isometric view of the
resilient gate seat and associated parts of the knife gate
valve of Fig. 1.
Fig. 6 is a front elevation view of a second
preferred embodiment of the knife gate of the present
invention that is shown with the knife gate in the closed
position.
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Fig. 7 is a front elevation view of the knife gate of Fig. 6 that is shown
partly in
cross section with the knife gate in the closed position.
Fig. 8 is an isometric view of a first body member of the knife gate valve of
Fig. 6.
Fig. 9 is an isometric view of the gate seat of the knife gate valve of Fig.
6.
Fig. 10 is an enlarged detail cross sectional view taken along lines 10--10 of
Fig. 6 showing the knife gate in a partly open position.
Fig. 11 is an enlarged detail cross sectional view taken along lines 10-- 10
of
Fig. 6 showing the knife gate in the closed position.
Fig. 12 is an exploded view of the cross sectional view of Fig. 10.
Fig. 13 is an enlarged cross sectional view of the gate seat taken along lines
10--10 of Fig. 6.
Detailed Description of Preferred Embodiments
A first preferred embodiment of the present invention is depicted in Figs. 1-
5,
which show a knife gate valve 10 that is comprised of a gate actuator assembly
12 and
a valve body assembly 14. Gate actuator assembly 12 moves a knife gate 16,
which
includes a blade portion 17, so that blade portion 17 either occludes or does
not occlude
a flow opening 18. A set of apertured flanges 20 permits the attachment of a
pair of
conduits (not shown) to knife gate valve 10 in alignment with flow opening 18.
Valve body assembly 14 is comprised of a first body member 22 having an
inner side 23 and an opposed outer side (not shown) and a second body member
24
having an outer side 25 and an opposed inner side (not shown). Body members 22
and
24 are fastened together by bolts 26 passing through second body member
unthreaded
bolt holes 28, which are located in a second body member rim 30, and first
body
member threaded bolt holes 32, which are located in a first body member rim
34. In an
alternative embodiment, first and second body members 22 and 24 are identical
with
threaded and unthreaded bolt holes interspersed so that when inner side 23 of
first body
member 22 is faced to the inner side (not shown) of second body member 24,
each
threaded bolt hole lines up with an unthreaded bolt hole. Skilled persons will
recognize
that other types of fasteners such as studs or pins, and combinations thereof,
can be
used.
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The bolted-together body members define a gate receiving space 36. A first
body member recess 38 combines with its mirror image (not shown) in second
body
member 24 to form a gate seat receiving recess 39 (Fig. 4). In this
configuration, the
term "inwardly" refers to the direction toward the plane at which body member
22
5 meets body member 24.
A flow axis 40 (Fig. 5) defines the axial dimension. The radial dimension
emanates outwardly from axis 40. A U-shaped resilient gate seat 42 occupies
gate seat
receiving recess 39 and includes multiple gate seat bolt holes 44 spaced apart
along its
U-shaped profile. When body members 22 and 24 are fastened together, bolts 26
extend through resilient gate seat bolt holes 44 to positively retain
resilient gate seat 42.
Rim 34 and rim 30 terminate in inwardly directed flanges 46 and 48,
respectively.
When bolts 26 are secured in place, flange 46 abuts flange 48 to thereby
define gate
receiving space 36 (Fig. 3) and gate seat receiving recess 39 (Fig. 4).
When they are in solid contact, flanges 46 and 48 ensure that the width of
gate
seat receiving recess 39 is uniform, resilient gate seat 42 is uniformly
compressed to an
optimal density, and the movement of resilient gate seat 42 is constrained.
When
valve 10 is in its closed position, blade portion 17 exerts pressure against
resilient gate
seat 42, potentially causing resilient gate seat 42 to deform away from blade
portion 17.
This deformation can cause leaks to develop through the seal between blade
portion 17
and resilient gate seat 42 . Flanges 46 and 48 form gate seat receiving recess
39,
which constrains the deformation of resilient gate seat 42 to establish a more
secure
seal.
Valve body assembly 14 is produced by fitting resilient gate seat 42 in gate
receiving recess 39 as body members 22 and 24 are mated. Body members 22 and
24
are secured together by bolts 26 extending through axially aligned body member
bolt
holes 28 and resilient gate seat bolt holes 44 and into bolt holes 32.
The assembly of prior art valves having two matable body members similar to
body members 22 and 24 but without flanges 46 and 48 requires extra attention
because
it is difficult to uniformly tighten bolts that function similarly to bolts 26
to secure the
body members together. When one of the bolts is tightened to a greater tension
than
another bolt, the resilient gate seat becomes unevenly compressed. This uneven
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compression can cause a less even seal between the knife gate and the
resilient gate
seat and permit leaks to develop between the resilient gate seat and the body
members.
With the assembly method of the present invention, bolts 26 are tightened
until flange
46 firmly abuts flange 48, thereby preventing further tightening. Bolts 26 are
easily
tightened until a hard stop is reached caused by the uniform meeting of flange
46 and
flange 48, and, consequently, resilient gate seat 42 is compressed uniformly.
With particular reference to Figs. 1, 2, and 3, gate actuator assembly 12,
which
is a standard feature in gate valves and is familiar to skilled persons, is
secured to the
upper portion of body assembly 14. Assembly 12 supports a stem nut 50 through
which a valve stem 52 is threaded. The lower end of valve stem 52 is secured
to the
upper end of knife gate 16 by a pair of bolt assemblies 54 (one shown in Fig.
3). A
hand wheel 56 is connected to stem nut 50.
Tuming hand whee156 in one direction moves knife gate 16 downward, thereby
inserting blade portion 17 into gate seat receiving recess 39 and into contact
with
resilient gate seat 42 to close valve 10. Likewise, turning hand wheel 56 in
the
opposite direction moves knife gate 16 upward, thereby retracting blade
portion 17
from gate seat receiving recess 39 to open valve 10.
Those skilled in the art will recognize that other types of actuators are also
possible. For instance, an electric motor or a pneumatic device could be used
to move
knife gate 16 between its open and closed positions. A packing gland 60 is a
standard
feature in gate valves and is of a design familiar to those skilled in the
art.
A second preferred embodiment of the present invention is depicted in
Figs. 6-13, which show a knife gate valve 10' including a generally U-shaped
resilient
gate seat 100 having a pair of tab portions 102 at its ends. With reference to
Figs. 6-9,
first and second body members 22' and 24', when bolted together, define a
generally
U-shaped gate seat receiving recess 39' (Figs. 7, 10, and 11) that includes a
pair of
recess extensions 106 for receiving and retaining tab portions 102 of gate
seat 100.
With reference to Figs. 9 and 13, resilient gate seat 100 includes a seating
region 110 along its length and rib portions 112 and 114 protruding from each
side of
gate seat 100 and extending along the length of gate seat 100 adjacent seating
region
110. Rib portions 112 and 114 are compressed to a greater extent than the
remainder of
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gate seat 100 when knife gate valve 10' is assembled and gate seat 100 is
clamped
between body members 22' and 24'. This produces a region of increased density
at the
rib portions 112 and 114 for ensuring a tight seal. The uniform width of gate
receiving
recess 39' ensures that the compression and density of the gate seat 100 is
uniform
along the length of gate seat 100 when it is fastened between the first and
second body
members 22' and 24'.
In the second preferred embodiment, knife gate valve 10' includes an even
number of bolt holes 28', which are alternately threaded and unthreaded so
that body
members 22' and 24' are interchangeable. As shown in Fig. 8, body members 22'
and
24' also include supports 120 about the perimeter of flow opening 18' that are
raised
inwardly to inhibit lateral motion of knife gate 16' caused by flow of
material through
flow opening 18'. A plastic friction insert 122 is mounted on each of body
members
22' and 24' at the top of flow opening 18' and contacts knife gate 16' to
guide knife
gate 16' and provide lateral support.
With particular reference to Figs. 10-13, seating region 110 of gate seat 100
includes a flat contact area 128 positioned between a pair of shoulders 132
that extend
from contact area 128 along the length of gate seat 100 to form a generally
convex
cross section having a height 133. Contact area 128 has a width 134 that is a
fraction
(preferably one-half) of the thickness 136 of blade portion 17' of knife gate
16' to
reduce friction between blade portion 17' and gate seat 100 and to reduce the
force
required to move knife gate 16'. Knife gate 16' is sized to fit between the
sides of
U-shaped gate seat 100 so that the height 133 of seating region 110 of gate
seat 100 is
compressed by an amount ranging from approximately 0.040 cm (0.016 inch) to
approximately 0.120 cm (0.047 inch) to ensure a tight seal. When knife gate
16' is
lowered to its lowest point so that valve 10' is fully closed as shown in Fig.
11, the
height 133 of seating region 110 is compressed along an arcuate region 138
(Fig. 9) by
an amount ranging from approximately 0.040 cm (0.016 inch) to approximately
0.120
cm (0.047 inch). The convex design of gate seat 100 reduces the force
necessary to
open valve 10' while providing the proper amount of compression of gate seat
100
required for a leak-free seal when knife gate 16' is fully closed.
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It will be obvious to those having skill in the art that many changes may be
made to the details of the above-described embodiments of this invention
without
departing from the underlying principles thereof. For example, flange 46 may
be
omitted and flange 48 may extended to contact rim 30, or vice versa. The scope
of the
present invention should, therefore, be determined only by the following
claims.
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