Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The present invention relates to a valve for use in
a sludge pump system. The valve is used in pumping
systems, generally in combination with a displacement
pump.
The pumping systems are used to transfer aggressive,
abrasive and corrosive liquids containing granular
material such as sand, coal, ore, found, for example, in
mining waste. These liquids are frequently pumped over
long distances, often at high temperatures, and under
high pressures. Such conditions place extremely high
demands on the durability of the pumping systems
components including the valve.
Dutch Patent Application No. 8600545 describes a
valve for use in a pumping system with a metal to metal
contact surface, partially with a metal to elastic
material contact surface. The metal to elastic material
contact surface allows sludge material, which is present
between the contact surfaces when the valve closes, and,
as a result, is under extra high pressure, to escape via
grooves provided in the metal contact without causing
damage to the valve. The use of elastic sealing rings
under the conditions described above, creates new
problems, as are mentioned in the Dutch Patent
Application. In use, the elastic material wears very
quickly, thereby failing in its intended function. The
result is that the elastic sealing rings must constantly
be replaced. This results in shut down of the system,
with the attendant consequences, such as cost, etc.
Attempts have been made to avoid replacing the sealing
rings by using symmetrical rings. Thus, the rings which
were worn on one side could be reversed and reused.
However, even this approach has not been fully successful
and there has been a considerable decline in the use of
elastic sealing rings.
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OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to
provide a valve which overcomes the drawbacks of the
prior art.
It is a further object of the invention to provide a
valve for use in pumping systems which pump aggressive,
abrasive, and corrosive liquids containing granular
material, pumped over long distances and/or at high
temperatures and pressures which has a longer life and a
longer maintenance free period than the valves of the
prior art.
It is a still further object of the invention to
provide a valve which when used under the conditions
described above, possesses a longer lifetime than the
valves of the prior art which generally must be replaced
after one month of use.
Briefly stated, the present invention provides a
valve for use in pumping systems which pump aggressive,
abrasive and corrosive liquids containing granular
material, the pumping being over long distances and at
high pressures. The valve employs a pair of elastic
sealing elements which, respectively, have spherically
configured convex and concave surfaces that mate along a
spherical contact surface when the valve is closed to
effect leak-free seal of the valve, this arrangement
giving a more maintenance free valve and one having a
longer service life.
According to an embodiment of the invention, there
is provided, a valve suitable for use in a sludge system
comprising a valve body, guide means for guiding axial
movement of the valve body, an elastic sealing ring and a
metal supporting element on the valve body. The
supporting element and the elastic sealing ring each
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having a contact surface. A valve seat is provided in the
in the valve body, and it includes a metal part and an
elastic part and these each have a contact surface. The
contact surface on the metal supporting element and that
on the metal part, and the contact surface on the elastic
sealing ring and that on the elastic part, respectively,
are moved into contact with each other in a closing
movement of the valve body against the valve seat. The
contact surface on the elastic sealing ring is concave,
and that on the elastic part is concave, with the elastic
sealing ring being carried on the valve body and the
elastic part on the valve seat such that during valve
closing movement, the elastic sealing ring and the
elastic part contact each other only along the respective
contact surfaces of each. The radius of curvature of the
elastic part concave surface is smaller than the radius
of curvature of the elastic sealing ring convex surface
whereby a first point of contact between the contact
surfaces of the elastic sealing ring and elastic part
occurs at a radially outermost location of the contact
surfaces. The metal supporting element and the metal
part, respectively, are carried on the valve body and the
valve seat, respectively, such that during valve closure
movement the two contact each other only and along the
contact surfaces of each.
The above and other objects and advantages of the
present invention will become apparent from the following
description read in conjunction with the accompanying
drawings, in which like reference numerals designate the
same element.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of one embodiment
of valve made according to the invention;
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FIGS. 2a and 2b depict wear that can occur on the
metal-to-metal contact surfaces of a valve of the prior
art; and
FIGS. 3a and 3b show how the contact surface wear of
the prior art is avoided by providing an undercut in the
valve body of the FIG. 1 valve.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the valve embodiment 1 depicted in FIG.
1, it may be used, for example, as a suction or delivery
valve in pumps such as displacement pumps for pumping
mixtures containing liquid and solid materials.
Valve 1 contains a high pressure side 2 and a low
pressure side 3. When the valve is closed, the pressure
in side 3 is lower than in side 2. Valve 1 has a valve
casing (not shown), and a valve body 5 which can move in
such valve casing. Attached to valve body 5 is valve stem
6 which will be mounted in the valve casing in such a
manner as to be moveable in sleeve 7. Sleeve 7 will be
attached to the valve casing with securing means shown
generally at 4.
If valve 1 is of the self-working type and is moved
by the pressure of the medium at sides 2 and 3 of the
valve, then a spring depicted in phantom at 8, is placed
between valve body 5 and sleeve 7 in the valve casing. If
the valve is not of the self-working type, then the
movement of valve body 5 will be effected by way of means
(not shown), which are operated outside the valve.
Located in valve 1 is valve seat 9, which has a
generally spherical contact surface. Valve body 5 has a
corresponding spherical contact surface. Valve body 5 has
a metal supporting element 10 which defines a spherically
contoured metal-to-metal contact surface 11.
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An elastic ring 12 is mounted on valve body 5.
Elastic ring 13 is mounted on valve seat 9. Both rings 12
and 13 have corresponding contact surfaces which form the
elastic contact surface 14.
The internal and external diameters, respectively,
of rings 12 and 13 are such that when valve 1 closes,
rings 12 and 13, first make contact at a point shown at
19. This point 19 is the radially outermost point of
common contact between the elastic contact surface
between the rings 12 and 13. When the valve body 5 moves
downwardly fully, the metal-on-metal contact between
valve seat 9 and the metal element 10 is effected. In
this process, the elastic ring 13 in the valve seat gives
away outwardly and presents a bulging section as 18.
It is desirable that the distinct contact surfaces
11 and 14, which are preferably bordering each other have
a curved configuration whereby one of the contact
surfaces may be concave and the other convex, as shown in
FIG. 1, ring 12 in that embodiment being convexly curved
and ring 13 concavely curved. The contact surface
curvature conveniently is, as noted above, of spherical
configuration. Other curvature forms such as elliptical
also can be used. The curvature though will be such that
the radius of curvature of the concave surface of ring 13
is smaller than that of the convex ring 12, this being
such as to insure first contact between the valve body
and valve seat during downward body movement occurs at
point 19.
Sealing ring 12 is constructed in such manner that
its largest diameter is larger than the diameter of the
elastic contact surface 14. Thus, under conditions of
either surface wearing or deterioration particularly of
the elastic particular at an uppermost lip section 15 of
the ring 13, a good seal at surface 14 still is obtained.
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The largest diameter defined by contact surface 14
is about equal to the largest diameter of a ring holder
plate 16 which encapsulates or mounts ring 12, such
element being attached as a part of valve body 5. In the
event of wear of a bulging section 18 of ring 12, the
diameter will be restored to that of the encapsulating
element 16, and no stair-like wear will occur.
An annular cutout 20 is made along the circumference
of the underside of element 10 in such a way that, if the
receiving surface of element 10 becomes worn, the contact
surface 11 will not show a stair-like wear pattern,
whereby element 10 would partially drop between the walls
21 of element 7 and closely adjacent these walls which
define at the top parts thereof, the metal contact
surface 11. Such drop if closely adjacent the walls,
undesirably would cause wear in round shape at the upper
edges of the walls.
FIGS. 2a and 2b show the undesirable wear effect
which can result where no undercut exists. FIG. 2a shows
how metal-to-metal contact surface 11 exists in a valve
where no or only little service use has taken place. With
use though, the regions 40, 41, respectively, in the
elements 10, 17 wear due to repeated contact taking place
during closings. This wear can become so severe that as
seen in FIG. 2b, rounding as at 42 at the top or contact
surface of element 17 develops. Further, the step or
stair-like effect of the lower face of element 10
entering between the walls 21 of the element 17 is
produced. The sum effect is that the geometry of the
contact surface between the elements 10 and 17 is
completely changed leading to failure of seal and
resulting leakage at that location.
FIGS. 3a and 3b shown how this is overcome. In FIG.
3a, the full undercut 20 is shown. With use, wear takes
place only at the contacting surfaces of elements 10, 17.
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Due to the undercut, no structure part of the element 10
can serve to form a corner around the lower or inner
point of the contact surface 11 of element 17. Hence,
there can be no rounding wear produced at that location.
In the prior art where a metal contact to elastic
material contact surface is employed, it has been found
that the high degree of wear of elastic material in the
valve of the prior art can be attributed to particles in
the sludge, which due to their presence on the metal
contact surface during the closing of the valve, are
pushed or forced into the contact surface side presented
by the elastic material only (they cannot in any
appreciable manner enter the metal surface side)
resulting in heavy damage in a short period of time to
the plastic. In contrast, in the present invention, the
aforesaid particles are elastically embedded or held in
or between the two elastic contact surfaces presented by
these rings during valve closing, this happening in such
manner that there is just minor deformation of the rings
elastic surfaces, with the result that upon opening, the
solids are freed from the surfaces without having caused
damage to the ring surfaces.
In using common elastic materials, the life of the
elastic materials is prolonged, so that the times between
maintenance are increased, which reduces costs. In known
sludge pump systems, it is usual to subject the solid
particles in the media to be transported to a pre
transport reduction process to sufficiently reduce the
size of the particles. This reduction process can be
reduced by using the valve as claimed herein, without
risking damage to the valve by sludge particles having a
large average size due to the two sided elastic embedding
of the sludge particles trapped between the elastic
sealing rings of the valve during closing.
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The presence of the metal supporting elements in the
valve of this invention support the elastic material of
the sealing rings of the valve body and the valve seat.
The valve so constructed is suitable of sustaining
working pressures in the order of from 30 to 300 bars.
In a preferred embodiment of this invention, the
cross section of the sealing rings and the elements is
chosen in such a way that when the valve body is moving
in the direction of the valve seat, the sealing rings are
the first to come in contact with each other, first at
the top and progressively downwards. The advantages of
this embodiment is that besides the two sided embedding
of the sludge particles in the elastic contact surface
during valve closure and the coming together of the
contact rings, just before closure of the metal
supporting elements, the metal contact surface concerned
is cleaned by the sludge as it escapes from between the
surfaces .
Also, in the valve according to this invention, the
point of the elastic contact surface which lies opposite
to that point where the contact surfaces touch each other
has sufficient freedom to execute a radial motion with
respect to the motional axis of the valve body. The
freedom to execute this motion forms a basis for making
the elastic contact surface curvilinear. It is preferred
to have a curved contact surface between the elastic
sealing rings, particularly a contact surface with a
spherical form. Therefore, if the descent of the valve
body is not perfectly straight arising, for example, from
play in the guiding means, it is less likely to result in
an incorrect seating, so that wear will not significantly
increase.
As far as the wear process of the respective contact
surfaces is concerned, the geometry of the contact
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surfaces plays an important role. Thus, the following
criteria should be met:
a) the maximum external diameter of the elastic
sealing ring of the valve body is a maximum of 1.05 times
larger than the maximum diameter of the contact surface
concerned;
b) the maximum external diameter of the elastic
sealing ring of the valve body is a maximum of 1.05 times
larger than the maximum diameter of an encasing element
or ring holder plate to which the sealing ring is mounted
at the high pressure side of the valve stem; and
c) an undercut should be made in the metal
supporting element at the low pressure side near the
metal contact surface.
These criteria ensure that, as the wear process
progresses, the geometry of the valve of this invention
remains the same, despite the fact that in the long term,
the valve body comes to rest in a progressively lower
position on the valve seat.
A further advantage of the incision is that, if the
supporting element becomes worn by the valve body, the
valve body will not fall between the supporting element
and the valve seat. Accordingly, stair-like wearing
effects on the metal contact surface are avoided.
Having described preferred embodiments of the
invention with reference to the accompanying drawings, it
is to be understood that the invention is not limited to
the precise embodiments and that various changes and
modifications may be affected therein by one skilled in
the art without departing from the scope or spirit of the
invention which is limited only by the appended claims.
