GATE ALIGNMENT MEANS AND METHOD FOR MINIMIZING LEAKS IN A KNIFE GATE VALVE

MOYEU D'ALIGNEMENT DE LA VANNE ET METHODE POUR MINIMISER LES FUITES DANS UN ROBINET-VANNE A GUILLOTINE

English Abstract

Gate alignment means for a knife gate valve in which oppositely-disposed
members on respective sides of a body for slidingly receiving a gate are
mounted to extend transversely into the body in abutment with the edge of
the gate and adjusted so that the space between the members corresponds to
the width of the gate. The invention finds use in minimizing leaks at the
packing in prior art knife gate valves.

French Abstract

Dispositif d'alignement de vanne pour robinet-vanne à guillotine dans lequel des éléments disposés vis-à-vis sur les cotés respectifs d'un corps pour permettre le coulissement d'une vanne sont montés de manière à dépasser transversalement dans le corps en aboutement avec le bord de la vanne et ajustés de manière que l'espace entre les éléments corresponde à la largeur de la vanne. L'utilité de la présente invention est de réduire les fuites à la garniture des robinets-vannes à guillotine des antériorités.

Claims

CLAIMS
1. Gate alignment means for a knife gate valve having a substantially planar
gate with a perimetric edge, the gate being slidingly received in a hollow body
defining an opening for material flow, and an actuator for sliding the gate in
a longitudinal direction through the body into and out of registration with
said opening, the body having at least one guide adjacent said opening to bias
the gate into sealing engagement with the body in a closed configuration of
the valve, the gate alignment means comprising at least one pair of members
oppositely disposed on respective sides of the body and extending into the
body transversely to said longitudinal direction in abutment with the
perimetric edge of the gate, the members being adapted to maintain alignment
of the gate inside the body during said biasing so that material leaks from the
body are minimized.
2. Gate alignment means in accordance with Claim 1 in which the members
each comprise a threaded pin and the body has respective threaded apertures
for receiving the pins, the separation between respective pairs of pins being
adjustable so as to correspond to the width of the gate.
3. Gate alignment means according to Claim 2 in which the pins have a
smooth internal end for abutment with the gate.
4. Gate alignment means according to Claim 3 in which the internal end is
rounded.
5. Gate alignment means according to Claim 2 in which a socket is formed
in an external end of the pin which is adapted to receive a cooperating tool
whereby the relative penetration of the pin to the body may be adjusted.
6. Gate alignment means according to Claim 2 in which a cap nut is threaded

on an external end of the pin.
7. Gate alignment means according to Claim 2 in which the threaded
apertures are defined in bosses integrally formed with the body.
8. Gate alignment means for a knife gate valve having a substantially planar
gate with a perimetric edge, the gate being slidingly received in a hollow body
defining an opening for material flow, and an actuator for sliding the gate in
a longitudinal direction through the body into and out of registration with
said opening, the body having at least one guide adjacent said opening to bias
the gate into sealing engagement with the body in a closed configuration of
the valve, the gate alignment means comprising at least one pair of threaded
pins received in respective threaded apertures oppositely disposed on
respective sides of the body, the pins extending into the body transversely to
said longitudinal direction in abutment with the perimetric edge of the gate,
the members being adapted to maintain alignment of the gate inside the body
during said biasing so that material leaks from the body are minimized.
9. In a knife gate valve having a substantially planar gate with a perimetric
edge, the gate being slidingly received in a hollow body defining an opening
for material flow and an actuator for sliding the gate in a longitudinal
direction through the body into and out of registration with said opening, the
body having at least one guide adjacent said opening to bias the gate into
sealing engagement with the body in a closed configuration of the valve, the
improvement in which the knife gate valve has gate alignment means
comprising at least one pair of members oppositely disposed on respective
sides of the body and extending into the body transversely to said
longitudinal direction in abutment with the perimetric edge of the gate, the
members being adapted to maintain alignment of the gate inside the body
during said biasing so that material leaks from the body are minimized.

10. A method of minimizing leaks in a knife gate valve having a substantially
planar gate with a perimetric edge, the gate being slidingly received in a
hollow body defining an opening for material flow and an actuator for sliding
the gate in a longitudinal direction through the body into and out of
registration with said opening, the body having at least one guide adjacent
said opening to bias the gate into sealing engagement with the body in a
closed configuration of the valve, the method comprising adding at least one
pair of members so that the members are oppositely disposed on respective
sides of the body and extending into the body transversely to said
longitudinal direction in abutment with the perimetric edge of the gate, the
members being adapted to maintain alignment of the gate inside the body
during said biasing so that material leaks from the body are minimized.
11. A method of minimizing leaks in a knife gate valve in accordance with
Claim 10 in which the members each comprise a threaded pin and respective
threaded apertures are formed in the body to receive the pins, the separation
between respective pairs of pins being adjusted to correspond to the width of
the gate.

Description

-- 21 67962
GATE ALIGNMENT MEANS AND METHOD
FOR MINIMIZING LEAKS IN A KNIFE GATE VALVE
This invention relates to a knife gate valve commonly used in industry to
obstruct and regulate the flow of material through a pipe conduit.
Knife gate valves are well-known and have been used for many, many
years. Such valves essentially comprise a body that defines an opening
through which material can flow. Typically, the opening is bordered by a
flange on opposite sides of the body so that it may be connected to a pipe or
other tubular conduit. The body is hollow and slidingly receives a gate
which is actuated so as to obstruct the opening or to open it, as the case may
be. The body is usually provided with packing, such as Teflon~-impregnated
fibre that surrounds the gate where it exits the body during actuation so as
to seal the gate to the body.
It has been found that material flowing through the conduit will often leak
from the valve in the area of the packing and that this may result from
compression of the packing when the gate is biased by guides for seating the
gate into the opening.
An object of this invention is to minimi7e leaks in knife gate valves arising
at the packing.
In accordance with this invention, there is provided gate ~lignment means
for a knife gate valve having a substantially planar gate with a perimetric
edge, the gate being slidingly received in a hollow body ~lefining an opening
for material flow, and an actuator for sliding the gate in a longitudinal
direction through the body into and out of registration with said opening, the
body having at least one guide adjacent said opening to bias the gate into
sealing engagement with the body in a closed configuration of the valve, the
gate alignment means comprising at least one pair of members oppositely
disposed on respective sides of the body and extending into the body
transversely to said longitudinal direction in abutment with the perimetric
edge of the gate, the members being adapted to maintain alignment of the gate

21 67962
inside the body during said biasing so that material leaks from the body are
.
mln1ml7.ed.
In order that the invention may be more clearly understood, a preferred
embodiment is described below with reference to the accompanying drawings,
in which:
Fig. 1 is a perspective view of a knife gate valve embodying the invention;
Fig. 2 is a cross-sectional view taken on lines 2-2 of Fig. 1;
Fig. 3 is a schematic cross-sectional view through a prior art knife gate valve;and
Fig. 4 s a similar view to Fig. 3 through a knife gate valve embodying the
mventlon.
A knife gate valve in accordance with the invention is shown in Fig. 1 and
generally indicated by numeral 20. The conventional components of the
valve 20 will first be described. The valve 20 comprises a hollow body 22
which defines a circular opening 24 through which material may flow.
Typically, a conduit 26 carrying the material is secured by peripheral flanges
28 (of which only one is shown in Fig. 1) to opposite sides of the body
adjacent the opening 24 and mounted on peripheral flanges 30,32 formed in
the body adjacent the opening 24. In the embodiment drawn, a series of
radially-spaced lugs 34 are formed with the flanges 30,32 and are apertured
to receive threaded fasteners such as bolt 36.
The upper part (as drawn) of the body 22 is a hollow sleeve that slidingly
receives a gate 38. The gate is a plate having a substantially-planar surface 40and a perimetric edge 42. The upper part (as drawn) of the gate 38 is
substantially rectangular and, at the bottom, it is curved to a radius which
corresponds with the radius of curvature of the associated circular opening 24.
A bevel 44 is m~chined at the bottom curved edge of the gate 38.
The gate 38 is lowered and raised into and out of registration with the
opening 24 by means of an actuator generally indicated by numeral 46 and
comprising a threaded rod 48 mounted to an upper portion 50 of the
peripheral edge of the gate 38. The rod 48 is rotatably received through the

21 67962
threaded hub 52 of a turning wheel 54 which is spaced from the body 22 by
means of four spacing rods 56. The rods 56 extend between the body 22 and
a platform 58 having an upwardly-extending collar 60 on which the hub 52
rests and are of sufficient length to accommodate the gate when it is out of
registration with the opening 24.
The walls of the body 22 diverge at the top to form a stuffing box 62
topped by a peripheral flange 64 having threaded apertures for receiving the
afore-mentioned spacing rods 56. The stuffing box 62 is filled with packing
66 which typically comprises a length of Teflon~-impregnated fibre and
which may vary according to the environment in which the valve 20 is to be
used. A packing gland 68 is dimensioned to be received inside the stuffing
box 62 and has a peripheral flange 70 which is urged toward flange 64 by
means of a plurality of threaded fasteners 72 disposed in respective threaded
apertures provided in both of the flanges 70, 64.
A pair of bevelled guides 74 is disposed at the bottom of the opening 24
on the internal surface of one of the flanges t30). Upon lowering of the gate
38 using the actuator 46, the bevel 44 is brought into engagement with the
guides 74 and is biased against a seat 76 formed on the inside of the opposite
flange 32 (see Fig. 2).
As mentioned above, the guides 74 are typically provided in pairs and are
radially spaced in the opening 24. It has been discovered that, when the gate
38 is brought into a closed configuration and lowered as indicated by arrow
78 in Figs. 2-4, the bevel 44 on the gate 38 inevitably makes contact with one
of the guides 74 before the other. As shown schematically in Fig. 3 of the
drawings, the gate 38 contacts the guide 74 drawn to the right of Fig. 3, while
still leaving a small clearance indicated by arrows 80 between the gate 38 and
the guide 74 drawn to the left of Fig. 3. This is an inevitable consequence of
inaccuracies resulting during m~chining which are within expected tolerances.
Effectively, the guide which first contacts the gate 38 operates as a fulcrum
whereby the gate is tilted out of alignment as indicated by arrow 82 into a
position shown in chain-dotted outline in Fig. 3. Upon such tilting, the

peripheral edge 42 of the gate 38 is brought i2nto contact with the packing 66
and compresses the packing 66 at the left of Fig. 3. When the gate 38 is fully
seated in the body 22, the second guide 74 returns the gate 38 into
longitudinal alignment within the body 22. Meanwhile, the compressed
packing 66 does not resume its original shape but leaves a groove where it has
been compressed by the edge 42 of the gate 38 and material flowing through
the opening 24 of the valve can leak through that groove.
In order to prevent such tilting arising at the guides 74, the invention
provides gate alignment means in the embodiment shown, the ~lignment
means comprising a first and second pair 84,86 of threaded pins oppositely
disposed on respective sides of the body 22, the pins ~ten~ing into the body
transversely to the arrow 78 and in abutment with the perimetric edge 42 of
the gate 38. It will be understood that the pins 84, 86 are proud of the
internal wall of the body 22. The pins 84,86 are received in respective bosses
88,90 formed in the body 22 and having apertures with a cooperating thread
adapted to mate with the pins 84,86. The inner end of the pins 84,86 are
rounded so as to make point contact with the gate 38 as it slides into and out
of registration with the opening 24. The outer end of the pins 84, 86 (Fig.
1) have a socket termination adapted to cooperate with an Allen key so that
the relative penetration of the pin to the body can be adjusted and the
separation between a pair of pins will correspond to the width of the gate 38.
Two pairs of cap nuts 92,94 are threaded on the pin pairs 84,86 respectively
and abut on the bosses 88,90.
In use, the conventional components of the valve 20 are assembled into
their operative positions. The gate 38 is lowered and retracted as usual to
ensure that it seats properly in the opening 24. The pin pairs 84, 86 are
mounted to the body 22 and adjusted to make point contact with the gate 38
as it slides inside the body. The packing 66 is then introduced into the
stuffing box 62 and packed using the packing gland 68 to complete the
assembly.
If an existing valve was refurbished to incorporate the invention, the

a,~qc9a
existing packing would be disposed of, the wàlls of the body 22 would be
drilled to receive at least one pair of oppositely-disposed pins and the pins
would be adjusted prior to inserting a new packing into the stuffing box.
It will be understood that several variations may be made to the above-
described embodiment of the invention without departure from the appended
claims. As will be apparent to those skilled in the art, such knife gate valves
come in various sizes and it is contemplated that, for smaller sized valves, forexample, having an opening diameter of 6" or less, only one pair of
oppositely-disposed pins would be sufficient, whereas in valves where the
opening diameter exceeds 20", three pairs of such pins may be required. It is
also envisaged that the alignment means may take different forms and will
generally comprise a member extending into the body transversely to the
direction of motion of the gate.

Representative Drawing