Note: Descriptions are shown in the official language in which they were submitted.
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Non-return valve for pulsating burners
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The present invention relates to a non-return valve in
the air inlet of a pulsating burner, which may be of the
type described in the US Patent 3 267 986 (K B OLSON) .
and 3 267 985 (J A KITCHEN).
The combustion air is inducted to the combustion chamber
via a non-return valve, fuel being mixed into the air
after the non-return valve. The fuel may be liquid,
gaseous or pulverulent.
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The non-return valve opens and closes under the action
of the sub- and excess pressure phases obtained in con-
junction with the pulsating combustion. Since these phases alternate with a frequency of 60 pulses per second
or more, for example, it is a question of very rapid
cycles and accordingly extremely short intervals, during
which the non-return valve shall reach its open position,
remain in its open position and then close.
In accordance with the US Patent 3 267 986, the non-
return valve comprises a plurality of resilient steel
-- leaves, fastened at one end to form flexible tongues.
A disadvantage with these is that they afford a rapidly
increasing resistance to opening from the closed position,
resulting in that they must be set slightly open in the
initial position. When they are kept in the closed
position during operation, there is thus an initial
force co-acting to initiate opening of the valve tongue
when it is subjected to the sub-pressure phase. Since
there are a plurality of such valve tongues, this results
in certain difficulties in achieving the same setting
of all the tongues. Furthermore, the valve tongues are
not exactly the same with regard to their spring pro-
parties, resulting in that they can have different
attitudes in the fully open position. The fully open
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position can furthermore change to a greater or less
extent with tumid to fatigue occurring in the tongues.
The resilient valve tongues thus involve certain Defoe-
gullies in achieving desired precision in the opening
and closing movements of the valve, and maintaining
this precision for long operational-periods. A further
i disadvantage is that the valve tongues cannot be opened
as rapidly as desired at the beginning of the sub-
pressure phase, since the opening movement is braked by
the spring bias of the tongue after the tongue has
passed said initial position where it is somewhat open.
The US Patent 3 267 985 describes the use of lamely
which are situated loosely on a seating and may be lifted
from it to a given end position determining the complete-
lye closed position of the valve. A condition with this
type of valve is that the apparatus is mounted vertically
so that the lamely are acted on vertically by gravity.
The lamely are disposed loosely on an abutment plate
with orifices, such that excess pressure gas can be led
through these holes to a lamely when it is to be lifted
into engagement with the seating above it for closing
its inlet opening. A plurality of such non-return valves
of comparatively small size must be used to obtain the
necessary rapidity in the opening and closing movements.
Each lamely must be controlled by axial guide means at
the edge of the lamely, resulting in varying friction
against its guide means and a certain risk that the non-
return valves will operate with relatively different
degrees of frictional resistance. In turn, this involves
the risk that some valves will open or close more rapidly
than others, and in its turn this can lead to operational
disturbances of a more or less serious nature. Further
to this there is the situation that during the sub-
pressure phase, induction air should be distributed as evenly as possible in order that the lamely of all the
valves will be actuated as uniformly as possible. This
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also applies during the excess pressure phase, when the
excess pressure shall lift the lamely to the closing
position. If the valves are subjected to different sub-
pressures or excess pressures, this may also result in
operational disturbances. In addition to this, there is
the fact that the loose lamely are to a certain extent
dependent on the apparatus retaining a constant vertical
attitude, since the function of these valves is based
on vertical reciprocating displacement of the Lyle.
Thus, if the apparatus is fitted in a ship, for example,
there is the risk that the lamely are effected by
lateral forces striving to deflect them from their normal
path of motion, which may in turn result in operational
disturbances as well.
As far as impulse burners are concerned, it is energy
applicable that the non-return valve, or valves, must
operate with the least possible resistance in order to
open and close rapidly, a further desire being that
these movements shall be as distinct as possible and
that they shall accurately adapt themselves to the
pulsating combustion cycle, thereby to achieve effective
combustion. None rapid opening and closing also enables
higher heating power. A still further desire is that
the non-return valve will be simple and cheap to menu-
lecture, and easy to fit ox exchange if so required.
The object of the present invention is to provide a non-
return valve for a use burner which eliminates the
disadvantages with the known non-return valves as far
as possible.
With this object in mind, the invention is based on a
non-return valve operating with a ring, known per so,
which is thin and flat and of elastic material such as
steel or plastics. Such a ring is illustrated in the US
Patent 3 830 253, for example. However, according to
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this patent, the flat ring is deflected about a go-
metric axis at right-angles to the central axis of the
ring, so that in an open position the ring abuts against
an abutment surface constituting a part of a cylindrical
surface As soon as the known ring is lifted from its
closed position, the spring bias will accordingly begin
to grow immediately, which acts to retard the opening
- movement in the same way as with a spring non-return
valve tongue.
1 0
Starting from this known non-return valve, the invention
relates to a valve of the kind disclosed in the pro-
amble to the following main claim.
In accordance with the invention, such a non-return
valve has the distinguishing features apparent from
the characterizing portion of the following main claim.
Briefly, the invention involves the use of a thin flat
ring, known per so, of elastically flexible material,
which, according to the invention, is fitted in a new
and special way in order to utilize intrinsic properties
of the ring. These properties will be apparent from the
following consideration of a ring of thin elastic
material such as steel or plastics, for example, steel
with a thickness in the range of 0.15 to 0.30 mm. The
ring has an outside diameter of about 12 cm and an inner
diameter of about 7 cm, the width of the ring thus being
about 2.5 cm. If the ring is now held along one edge
circumference, either the outer or the inner, and a very
small force is applied axially along the other edge
circumference, the ring will deflect to an intermediate
position, which cannot be exceeded without the force
being increased very heavily and the ring being per-
manently deformed. The edge circumference of the ring thus has two distinct separate ranges of movement,
namely a first range where the axial force is extremely
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small, in the order of magnitude of some water column mm
acting on the surface of the ring, and a second range
where the force is many times greater, and results in
undesired permanent deformation of the ring.
In the first movement range, the ring will form a trunk
acted cone having varying size. When this cone approaches
I` the intermediate position mentioned above, the sloping
surface of the cone forms a very small angle to the base
thereof, in the order of magnitude 3. To deflect the
ring to the intermediate position from the initial or
flat position thereof thus requires practically no force,
-I i.e. it is extremely easy to come to the intermediate
position, which means that the material in the ring
affords very little resistance.
. .
With these properties of the ring in question in mind,
the invention is based on the concept that these proper-
ties can be utilized in an extremely advantageous way
in a non-return valve for a pulsating burner, with its
rapid alternations between sub- and excess pressure
I phases.
... . .
The ring is placed in a flat condition above an inlet,
preferably in a form of a plurality of induction open-
ins, or an induction slit, with one side of the ring
facing towards a duct to the combustion chamber, and I,
its other side facing towards the inlet communicating
with ambient air, suitably via a sub-pressure chamber.
In an embodiment of the invention, the edge or outer edge
portion of the ring is practically completely prevented
from moving axially by it being disposed with a very
small play in a slot, or the like. On the other hand,
the inner edge of the ring is free to move axially. In
practice, the fact that the play is not too small can be
established by it still being possible to turn the ring.
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In operation, one side of the ring will be subjected to
excess and sub-pressure phases caused by the combustion
in the combustion chamber, while its other side is acted
on by a varying sub-pressure_ The direction of force
S alternates in correspondence to the frequency of the
pulsating burner.
Practical tests with such a non-return valve in accord-
ante with the invention have shown that it opens and
closes-so rapidly that it is entirely open during the
. greater part of-the sub-pressure phase, which is desire
able. This result sin that the pulsating burner will be
more independent of varying operational conditions,
while improved combustion result is obtained at the
same time.
These and other details and advantages distinguishing
the non-return valve in accordance with the invention
will now be described in detail, with reference to the
accompanying drawings on which a non-return valve in
accordance with the invention is schematically ill-
striated, and whereon Figure 1 is a plan view of a flat .
and thin steel ring, Figure 2 illustrates the ring in
a flat attitude supported on an annular support and
held along its outer edge such that it may be
rotated, Figure 3 illustrates the ring upwardly de-
floated into the shape of a truncated cone, the height
of which is very small in comparison with the diameter
of its base, Figure 4 is a diagram illustrating the
force required to lift the inner edge of the ring as
in Figure 3, as a function of the angle between the
conical surface of the frustum and its base. Foggier
is a schematic section through the inlet of a pulsating
burner having a non-return valve in accordance with
the invention. Figure 6 is an enlarged sectional view of
the valve in open position.
The flat steel ring 10 illustrated in Figs 1-3 suitably
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has a thickness in the range of 0.15 to 0.30 mm. The
ring is supported on an annular support 11, and has its
inner circumference edge free to move axially upwards
in Fig 2. The outer circumference edge 14 of the ring
is practically completely axially fixed between a
lower support 15 and an upper support 16, with a very
small clearance, which however permits the ring to be
I- rotated.
If the ring is now loaded with an axial, circumferential
force, schematically illustrated by the arrow denoted
by P, the ring will be deflected upwards into the shape
_ of a truncated cone, the conical surface of which forms
- the angle V with the base 17 thereof. Simultaneously
; 15 with this upward deflection there is obtained a small
radial movement inwards of the outer circumference edge
of the ring, which is allowed by the minimum play be-
tweet the supports 14 and 15. Initially, the force P is
practically 0 and remains almost just as small until
the angle V reaches a value of about 3. Passing this
position can only occur if the force P is increased
Ann times and to-:valuPs which lead-to permanent
deformation of the ring.
If the force P is taken to correspond to mm of water
head Up, the graph according to Fig 4 may be plotted.
From the graph it will be seen that the force Pin mmVp
increases from 0 to a value A not very far away from 0,
namely only 2 mm Up, and remains constant in this
particular case up to 2.6 for the angle V between the
conical surface of the frustum and its base. This
force is thus so small that in practice it means that
the ring does not offer any resistance in the range of
; movement +/-2.6. However, if it is attempted to exceed
these limits, there will be immediate, total retard-
lion, since the required force increases practically
vertically upwards in the diagram.
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This property of the ring with the described method of
restraint at the outer circumference edge thereof in
combination with the ring being thin, and thus having
a very small mass, provides the properties of the ring
5 desired in a non-return valve for the rapid pressure
alternations occurring in a pulsating burner.
Fig 5 illustrates how a ring in accordance with the
invention is fitted as a non-return valve in a schema-
10 tidally illustrated pulsating burner 18.
A plurality of inlet openings 20 are made in an annular
seating 19. The seating may be flat (horizontal in the
- figurer somewhat sloping inwardly downwards. The thin
15 steel ring 10, implemented as illustrated in Figs 1-3,
is placed on the seating. The ring is practically come
pletely fixed in an axial direction along its outer
circumfer1enc~ edge, between the outer edge portion of r
the seating no the opposite edge portion f a wall 21.
20 The wall forms together with the seat an annular gap
in which the ring is movable between its end positions.
A small groove AYE is made at the outer edge of the
seating 19, in order to give the outer circumference
25 edge of the ring freedom of movement upwards and down-
wards when the ring is deflected upwards and downwards
for opening and closing.
In the vicinity of the inner edge portion of the ring
30 the wall 21 is hollowed out at 22 to uncover this edge
portion on its upper side BOA. The wall and seating
merge thereafter in the walls to an axial duct 23
leading to the combustion chamber 24. Fuel is injected
through a nozzle 25 and mixes with air before entering
35 the combustion chamber.
The air is inducted via a sub-pressure chamber 26.
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As will be seen from the enlarged partial depiction of
the non-return valve in Fig 5, the ring in this figure
has been deflected upwards to the fully open position.
Since the ring itself determines its maximum opening
position, there is no need of any abutment limiting
the opening movement of the ring. Instead, there is I
a gap between the wall 21 and the ring in its open
I` position, such that excess pressure may act in this
gap for closing the valve.
The intention with the uncovered inner edge portion
of the ring is that when the excess pressure pulse
reaches the inner circumference edge of the ring for
closing the valve, this pressure wave will be guided
upwards from the axial duct 23, into the hollowed-out
portion 22 of the wall, and then downwards towards the
upper side of the free edge portion BOA, thereby cocci-
in in a rapid and reliable closure. Initiation of the
closing movement will therefore be very effective and
distinct.
The invention is naturally not limited to the embodiment
described herein before. In certain cases it may be suit-
able to combine a plurality of non-return valves in
accordance with the invention into a unit of co-axially
arranged rings and seats, this resulting, inter alias
in the advantage that the non-return valve can have a
smaller diameter, so that the unit takes up less room.
Thus, in a simple way, it is possible to build up the
non-return valve in accordance with the invention to a
desired capacity, enabling the provision of differently
sized non-return valves simply and cheaply independent
of desired through-flow in the case in question.
The invention has been described in conjunction with a
steel ring, but this may also be replaced to advantage
by a plastics ring in certain cases.
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As disclosed above, the basic feature of the invention
is to substantially prevent the outer edge of the ring
to move axially and to obtain opening substantially by
flexing the ring to the shape of a truncated cone.
Since there is always a certain play at the outer edge
of the ring which preferably should be kept as small
as possible to obtain best result, the opening of the
valve is also dependent on the small axial movement
allowable by said axial play. In certain applications
it may be necessary to increase this axial play within
certain limits-to obtain a greater through-flow in the
valve. However, this will result in a decreasing
efficiency which to a certain degree may be acceptable
in order to permit for example a greater diameter of
the pulse pipe, that is the outlet pipe from the
combustion chamber.
