The present invention relates to a spray device for
spraying a liquid, the device comprising at least one
vessel, a transducer placed in the vessel, and a feed
circuit for filling the vessel with the liquid to be
Such a device is described, for example, in French
patent of invention No. 2 721 839.
The liquid present in the vessel, as renewed by the
feed circuit, participates in cooling the transducer and
in removing the mechanical energy generated thereby.
The invention seeks in particular to avoid the
transducer overheating if the supply of liquid in the
vessel is insufficient.
It achieves this by the fact that the spray device
includes a sensor organized to deliver a signal
representative of a given state of operation of the feed
circuit, and control means for interrupting the operation
of the transducer when said signal crosses a
In particular, it is possible to deliver a signal
representing the flow of liquid in the feed circuit.
In a particular embodiment of the invention, a
pressure sensor is used, which has the advantage of being
relatively insensitive to variations in the inclination
of the spray device.
When the feed circuit includes a pump, the pressure
sensor is placed, for example, downstream from the pump
and upstream from the vessel, and the control means
interrupt the operation of the transducer when the
pressure measured by the sensor drops below a
Because of the invention, it is easy to detect a
failure of the feed circuit due, for example, to the pump
stopping, to a leak from the pipework connecting the pump
to the vessel or to its own feed tank, or indeed to said
tank being empty.
This ensures that the transducer does not operate
with an insufficient quantity of liquid in the vessel.
It may also be advantageous to improve the
efficiency of the spray device, i.e. the ratio of the
quantity of liquid sprayed in the form of droplets having
a predetermined size to the quantity of liquid injected
into the vessel by the feed circuit.
This is achieved by ensuring that at least a
fraction of the liquid that is to be sprayed is injected
into the vessel with a non-zero axial component towards
the open end of the vessel.
With this particular embodiment, the turbulence of
the liquid in the vessel is reduced and a flow of liquid
at the outlet from the vessel is obtained which is much
more laminar than is the case in above-mentioned French
patent 2 721 839 where the liquid to be sprayed is
injected into the vessel in a purely radial direction.
Because the liquid flow towards the open end of the
vessel is less turbulent, the resulting droplets are more
uniform in size, and the spray device is more efficient.
Also preferably, a fraction of the liquid injected
into the vessel is directed onto the transducer, thereby
cleaning it and cooling it.
It is also advantageous to feed electrical power to
the transducer by using all or part of the vessel as an
This serves to simplify making electrical
connections with the transducer.
It can also be advantageous to feed the vessel from
a tank that is completely full of the liquid to be
This embodiment makes it possible to control more
accurately the characteristics of the jet of liquid
leaving the vessel, and to improve the effectiveness of
the spray device.
Also, by using a tank that is completely full, it is
possible to reduce variations in the flow rate of the
liquid feeding the vessel as a function of the
inclination of the tank, or as a function of variations
in pump operating rate.
It has also been found that this reduces the risk of
bubbles being present in the liquid feeding the vessel.
In an embodiment, the tank completely full of liquid
to be sprayed, referred to as the "downstream" tank
below, is fed by a pump which takes the liquid from
another tank, referred to as the "upstream" tank, with
the upstream tank being only partially full.
In an embodiment, the downstream tank overflows into
the upstream tank via an overflow orifice situated in a
high portion of the downstream tank so as to maintain a
column of liquid above the orifice(s) through which the
liquid for spraying is extracted from the downstream
Depending on the height of this liquid column, the
pressure of the liquid feeding the vessel(s) used for
spraying the liquid increases or decreases.
In another particular embodiment, instead of using
an overflow orifice, a pressure-relief valve or the like
is used to regulate the pressure in the downstream tank,
the liquid leaving via said valve flowing into the
upstream tank, which may be connected via an electrically
controlled valve to a liquid feed pipe for initial
filling and periodically delivering a quantity of liquid
that is to replace the liquid which has been sprayed.
The liquid which leaves the vessel(s) without being
sprayed is advantageously recycled via the upstream tank
by flowing over a sloping wall until it reaches it.
In this embodiment having upstream and downstream
tanks, it is particularly advantageous for the purpose of
detecting anomalous operation of the spray device to make
use of a differential pressure sensor which is suitable
for delivering a signal representative of the pressure
difference between the upstream tank and the downstream
Thus, using a single sensor, it is possible to
detect various kinds of anomalous operation, and in
particular the situation in which there is an
insufficient quantity of liquid in the upstream tank, the
situation in which said tank needs to be topped up again
to compensate for loss of liquid, and the situation where
either the upstream tank contains too much liquid or the
downstream tank is leaking or the pump is faulty.
The use of a differential pressure sensor makes it
possible to detect anomalous operation of the spray
device very quickly because of the particularly short
response time of this type of sensor.
It is also relatively easy to make such a sensor
In another embodiment having upstream and downstream
tanks, it is also advantageous to use a pressure sensor
for measuring the pressure in the downstream tank.
Naturally the various above-described embodiment
features can be implemented in combination or separately,
for their specific advantages.
To make the invention easier to understand, there
follows a description of various embodiments given as
non-limiting examples and made with reference to the
accompanying drawings, in which:
- Figures 1 to 5 are diagrams of five spray devices;
- Figure 6 is a diagram of a spray head.
The spray device 1 shown diagrammatically in Figure
1 comprises a tank 2 containing a supply of liquid to be
sprayed, e.g. water, and a spray head including an
elongate vessel 3 with a piezoelectric transducer 4 of
known type placed in the bottom thereof.
The cross-section of the vessel 3 tapers
progressively going away from the transducer 4 to an
The inside surface 6 of the vessel 3 is in the form
of a paraboloid of revolution to focus the ultrasound
emitted by the transducer 4 into the vicinity of the
The vessel 3 receives liquid taken from the tank 2
via a feed circuit 7 including a pump 8 which is
connected to the tank 2 via an intake duct 9 and to the
vessel 3 via an injection duct 10.
The transducer 4 is excited by an electrical
amplifier 1 which receives the high frequency signal
delivered by a signal generator 12.
An electronic switch 13 makes it possible to
interrupt the connection between the signal generator 12
and the amplifier 11.
In the example described, the electronic switch 13
is connected to a pressure sensor 14 disposed so as to
deliver a signal representative of the pressure of liquid
in the injection duct 10.
By way of example, the pressure sensor 14 may be of
a conventional membrane type.
While the spray device 1 is operating properly,
liquid is continuously injected by the pump 8 into the
vessel 3, at an absolute pressure lying in the range
102,000 Pa and 120,000 Pa in the embodiment described,
i.e. at a pressure increase lying in the range 2000 Pa to
A jet of liquid is formed leaving the opening 5 of
the vessel 3. The role of the transducer 4 is to act on
said jet of liquid to cause fine droplets of liquid to be
formed. The ultrasound waves emitted by the transducer
are concentrated by the surface 16 into the vicinity of
the opening 5, and when concentrated in this way, these
waves cause a mist made up of fine droplets to be emitted
from the jet of liquid, in conventional manner.
Reference may usefully be made to French patent
2 721 839 which describes a configuration enabling the
mist formed in this way to be removed by means of a fan,
e.g. for humidifying a vehicle cabin.
In the event of the pump 8 failing, for example,
then the pressure of liquid injected into the vessel 3
This pressure drop is immediately detected by the
pressure sensor 14 and the electronic switch 13 is
organized to interrupt the connection between the signal
generator 12 and the amplifier 11 when the pressure
measured by the pressure sensor 14 drops below a
predetermined threshold, e.g. set at 102,000 Pa, i.e. at
about 2000 Pa above atmospheric pressure.
This avoids damaging the transducer 4 which is no
longer being properly cooled by renewal of the liquid in
the vessel 3.
It is thus possible to counter the risk of the
transducer 4 being damaged in the event of a failure in
the circuit feeding liquid to be sprayed, and to do so at
relatively low cost and with a high degree of
As in the embodiment described, the pressure sensor
is preferably located so as to be swept continuously by a
flow of liquid, thereby making clogging unlikely.
The pressure sensor also has the advantage of being
capable of being used in any position, which is
advantageous when the spray device 1 is fitted to a
Naturally, the embodiment described above is not
Thus, without going beyond the ambit of the
invention, it is possible to place the pressure sensor
elsewhere on the liquid feed circuit, e.g. upstream from
the pump 8.
Under such circumstances, the electronic switch 13
is organized to interrupt the operation of the transducer
4 when the pressure upstream from the pump 8 exceeds a
predetermined value, representative of the fact that the
pump is no longer taking in liquid properly from the tank
It is also possible to place the pressure sensor so
that it delivers a signal representative of the pressure
of the liquid at the outlet from the injection duct 10.
It is also possible to place the pressure sensor in
the tank 2 so that it delivers a signal representative of
the pressure of the liquid at the inlet to the intake
duct 9, for example.
Also, without going beyond the ambit of the present
invention, it is possible to use a sensor other than a
pressure sensor, e.g. to measure the flow rate of the
liquid in the feed duct and to cause the transducer 4 to
be stopped in the event of the pump failing.
Any known flow measuring device can be used for this
Figure 2 shows a spray device 1' constituting a
variant embodiment of the invention.
The device 1' differs from the above-described
device 1 in the nature of the sensor 14' used to replace
the pressure sensor 14 for detecting an anomaly in the
liquid feed circuit to the transducer 4, and by the
presence in the feed circuit of a heat exchanger 15
through which the liquid sent to the transducer passes so
as to cool one or more electronic components, e.g.
certain components of the amplifier 11.
The sensor 14' may be constituted, for example, by a
flow meter delivering a signal representative of the flow
rate of the liquid in the injection duct 10, with the
electronic switch 13 being organized in such a manner as
to interrupt the connection between the signal generator
12 and the amplifier 11 in the event of the flow rate
dropping below a predetermined value.
In the embodiments described above, the electronic
switch 13 is placed between the generator 12 and the
In a variant, the electronic switch could be placed
between the amplifier 11 and the transducer 4.
Figure 3 shows a third embodiment of the spray
This device 1'' has two tanks separated by a common
partition, the liquid to be sprayed being pumped by a
pump 22 from a first tank 20, referred to below as the
"upstream" tank, and delivered into a second tank 21,
referred to below as the "downstream" tank.
The pump 22 is immersed in the downstream tank 21
which is completely filled with the liquid and which has,
at its top portion 25, a narrow section and an overflow
orifice 24, with liquid flowing under gravity from said
orifice 24 into the upstream tank 20.
In the example described, the spray device has two
spray heads with respective feeds of liquid to be sprayed
via ducts 26 and 27 both opening out into the downstream
The overflow orifice 24 is higher than the orifices
through which the ducts 26 and 27 open out into the
downstream tank, so the pressure of the liquid at the
inlets of these ducts therefore depends on the height of
the top portion 25 of the downstream tank 21.
A sloping wall 28 is provided to collect non-sprayed
liquid leaving the spray head vessels 3 and to guide that
liquid via a passage (not shown) through the upper
portion 25 of the downstream tank 21 into the upstream
A pressure sensor 30 is mounted in the outlet duct
of the pump 22 to detect anomalous operation, like the
pressure sensors 14 and 14' of the previous embodiments.
The spray device 1'' shown in Figure 3 has the
advantages of enabling the spray heads to operate
regardless of the inclination of the device and of
reducing the risk of bubbles of air being present in the
ducts feeding the spray heads.
In addition, regulating the pressure by means of an
overflow leading back into the upstream tank 20 enables
the spray device 1'' to be relatively insensitive to
variations in the operating rate of the pump 22.
In a variant that is not shown, the upper portion 25
of the downstream tank 21 and the overflow orifice 24 are
replaced by a pressure-relief valve which opens when the
pressure of the liquid in the downstream tank 21 exceeds
a predetermined value.
Figure 4 shows a spray device 1''' constituting a
fourth embodiment of the invention.
In this device 1''', pressure regulation in the
downstream tank, given reference 31, is provided by a
When the valve 32 opens, the liquid contained in the
downstream tank 31 drops into the upstream tank, given
reference 33 in this case.
The downstream tank 31 communicates via feed ducts
34 and 35 with respective spray heads.
A sloping wall 36 is provided to collect the liquid
that is not sprayed by the spray heads and to return it
to the upstream tank 33.
Figure 4 shows an electrically controlled valve 37
connected to a source of liquid for automatically filling
the upstream tank 33.
A pump 38 immersed in the downstream tank 31 enables
liquid to be taken from the upstream tank 33 and to be
delivered into the downstream tank 31, as in the
The upstream and downstream tanks 33 and 31 are
separated by a common partition 42.
A differential pressure sensor 40 is mounted through
said partition 42 to deliver an electric signal
representative of the pressure difference at the bottoms
of said tanks.
This single sensor 40 makes it possible to detect
and identify various kinds of operating anomaly.
More particularly, the sensor 40 delivers a voltage
V which can cross three levels V1, V2, and V3 where V1 >
V2 > V3.
When the voltage delivered by the sensor 40 is
greater than V1, that means that the height of liquid in
the upstream tank 33 is less than a height h1 which is
slightly greater than the height of the intake orifice of
the pump 38.
Control means are provided to trigger an alarm under
such circumstances to warn that the content of the
upstream tank 33 is too low.
When the voltage V lies between V2 and V1, that
means the height of liquid in the upstream tank 33 lies
in the range h1 to h2, with the valve 32 being slightly
higher than h2.
Control means are provided to open the electrically
controlled valve 37 when the voltage V lies between V1
and V2 to cause the upstream tank 33 to be filled.
This filling ceases when the liquid level reaches
the height h2, i.e. when the voltage V crosses the
When the voltage V is greater than V3 and less than
V2, that means that the height of liquid in the first
tank 33 lies in the range h2 to h3, the value h3 being
slightly lower than the maximum height liquid can reach
in the upstream tank 33. There is a risk of the upstream
tank 33 overflowing or there is a leak in the downstream
If the voltage V is less than V3, that may mean that
the pump 38 is not operating properly.
Control means (not shown) are provided to trigger an
alarm under such circumstances.
It will be understood that in this embodiment, using
a single differential pressure sensor and associated
control means, it is possible to obtain a considerable
amount of information, concerning the operating state of
the spray device.
Figure 5 shows a fifth embodiment of a spray device
implementing the invention.
In this device, the pressure in the downstream tank,
referenced 71, is regulated by a pressure sensor 70
placed at the base of the top wall 72 of the downstream
This pressure sensor 70 delivers information
representative of the height h of liquid above it, i.e.
the difference in height between itself and the top end
of the jet emitted by the vessel 3.
When the liquid level in the upstream tank,
referenced 73, decreases, then the height h of the jet
The pressure sensor 70 thus serves to deliver a
signal representative to some extent of the height of
liquid in the upstream tank.
When the height h has decreased by the quantity dh1,
or dh2, that means the level of liquid in the upstream
tank has decreased by an amount dh1' or dh2,,
respectively, and for a predetermined value of dh1', the
control means (not shown) to which the sensor 70 is
connected cause the electrically controlled valve 37 to
open and the upstream tank to be filled up to a reference
level, i.e. until the height h of the jet at the outlet
from the vessel 3 as measured by the sensor 70 has
returned to a predetermined value.
The threshold dh2 is selected to be representative
of abnormal operation of the device, and under
circumstances, the control means to which the sensor 70
is connected cause the pump 38 feeding the transducer
placed in the vessel 3 to be stopped.
Figure 6 shows a particularly advantageous way of
implementing the spray head, referenced 50 in this
figure, comprising a vessel 51 having an axis X, and a
In the spray heads described above, as in the prior
art, the liquid is injected into the vessel in a purely
radial direction, whereas in the embodiment of Figure 6,
at least a fraction of the liquid to be sprayed is
injected into the vessel 51 with a non-zero axial
component towards the open end 53 thereof.
This makes it possible to improve the efficiency of
the device, i.e. the ratio of the quantity of liquid
sprayed in the form of droplets of predetermined size to
the total quantity of liquid injected into the vessel by
the feed means.
This improved performance of the spray head is
explained by the fact that the flow of liquid towards the
open end 53 of the vessel 51 is less turbulent, thereby
giving rise to greater uniformity in the size of the
droplets which are formed.
The vessel 51 is fed from an annular cavity 54 which
receives the liquid via a duct 55.
The annular cavity 54 communicates with the inside
of the vessel 51 via an annular passage 56 that slopes
obliquely towards the axis X of the vessel and towards
its open end 53, and which is defined both top and bottom
by conical surfaces.
The liquid passing through the annular passage 56 is
directed towards the opening 53 which tends to make the
flow along the wall of the vessel 51 laminar while the
spray device is in operation.
The diameter d of the opening 53 is selected so that
the jet of water formed solely by the pressure of liquid
coming into the vessel 51 when the transducer is not
operating is substantially the same as the acoustic
fountain that would be generated by the soundwaves
emitted by the transducer on their own if the liquid
present in the vessel were static.
In the example described, the diameter d of the
opening 53 is 5.6 mm, the inside diameter D of the vessel
51 at its base is 18 mm and the length l of the vessel 51
is 38 mm.
The energy efficiency of spraying is increased
because the energy of the waves is used for the most part
to break the water up into droplets, the jet of water
being already formed by the pressure of the liquid
injected into the vessel 51.
The action of the ultrasound emitted by the
transducer 52 on the jet of water leaving the vessel 51
is to cause a mist to be formed that is made up of
droplets of relatively uniform size.
In the example described, the cavity 54 is formed by
assembling together a top piece 58 and a bottom piece 59.
The bottom and top pieces 59 and 58 have circularly
cylindrical walls about the axis X, which radially define
the cavity 54.
The cylindrical wall 60 of the bottom part 59 has a
radial hole 57 passing therethrough which opens out
slightly above the transducer 52 and which directs a
fraction of the liquid coming from the duct 55 into the
cavity 54 onto the transducer 52, thereby cooling it.
The electrical power supply to the transducer 52 is
advantageously provided using the vessel 51 and the
bottom and top parts 59 and 58 that include metal
portions to convey electricity.
In the example shown, the transducer has a contact
63 on its outside face which is connected to an
electrical power supply wire 64.
Electric current return is provided by a wire 67
connected to a contact 66 situated on the outside surface
of the vessel 51 and via a portion of the transducer 52
in contact with the bottom part 59.