EP0069741B1

EP0069741B1 - Positively controlled sound generator

Info

Publication number: EP0069741B1
Application number: EP81902814A
Authority: EP
Inventors: Per Börje FRANSMAN
Original assignee: Ekstroms Varmetekniska AB
Current assignee: Ekstroms Varmetekniska AB
Priority date: 1980-10-13
Filing date: 1981-10-13
Publication date: 1986-03-12
Also published as: DK250482A; EP0069741A1; DK152412C; FI823866L; SE8007150L; FI823866A0; SE425597B; FI71622B; NO152589B; NO821858L; WO1982001328A1; NO152589C; FI71622C; DK152412B

Abstract

A positively controlled sound producer for regulated delivery of pressure gas pulses from a pressure gas line (7) to a resonator (1). The sound producer comprises a valve sleeve (9) which is disposed coaxially on the pressure gas line and is rotatably mounted thereon by means of roller bearings (10), said valve sleeve being connected to a prime mover (6) and being provided with openings (14) for cooperating with openings (15) in the pressure gas line when the valve sleeve is rotated for regulating the delivery of pressure gas pulses from the pressure gas line.

Description

This invention refers to a sound generator for the infra sound range for regulated delivery of pressure gas pulses from a pressure gas line to a resonator comprising a resonance tube, the length of which substantially corresponds to one fourth of a wavelength of the sound generated in said sound generator, for keeping boilers or the like clean.
EP-A2-0 006 833 discloses a low-frequency sound generator comprising a resonance tube for keeping boilers or the like clean, said sound generator utilizing a movable valve slide member for generating the relevant sound.
Furthermore, DE-A-2 262 948 illustrates a sound producer for delivery of pressure gas pulses from a pressure gas line to a resonator. This sound producer comprises a valve member which is connected to a prime mover for being driven thereby so as to control the delivery of the pressure gas pulses from the pressure gas line. The valve member consists of a valve sleeve which is coaxially disposed on the pressure gas line and is rotatably mounted. The valve sleeve has one or more openings for cooperation with one or more openings in the pressure gas line when the valve sleeve rotates. This sound producer is actually a howl-generating siren, and thus it generates high-frequency sound.
The field of utilization of the sound generator according to EP-A-0 006 833 may vary, but as indicated by way of introduction said generator is primarily intended for the clean-keeping of boilers or other spaces through which dust-carrying gas flows. As a result of the open end of the resonance tube being connected for example to a boiler it becomes possible to keep dust from being deposited on pipes, walls and channels and in pockets.
Different types of dust and different spaces as well as different pressures (positive pressures or negative pressures) in the spaces can require different frequency ranges in order for the best results to be achieved and an appropriate frequency for any relevant space may be selected by the sound generator being made adjustable for different frequencies.
In order to achieve trouble-free operation of the sound generator and to enable accurate regulation of the frequency the sound generator of the above-mentioned type in accordance with the invention has been provided with the features which are set forth in Claim 1.
In the present invention sound is generated with a high level of intensity, wherein the frequency range of the sound may be varied by speed control so that the highest sound intensity is generated in different frequency ranges in contrast to the case with a so-called feedback system of known type which operates with a predetermined frequency, wherein the pressure gas pulses are supplied to the resonator by the valve device which controls the delivery of the pressure gas pulses from the pressure gas line being controlled by a diaphragm disposed in the resonator (EP-A-0 006 833).
In order to elucidate the invention an embodiment of the sound generator chosen as an example will be described more specifically in the following with reference to the accompanying drawings, in which Figure 1 shows a side view of a sound generator, comprising the sound generator in accordance with the invention, connected to a resonance tube, said sound generator being disposed for keeping a space clean and being shown with a compressed air system connected to the generator. Figure 2 is an axial sectional view of one end of the sound generator with the sound producer connected thereto, and Figures 3 and 4 are sectional views taken along the line A-A in Figure 2 showing two different variants of the sound producer.
The sound generator consists of a resonance tube 1 having an open end 2 and a closed end 3 and a sound producer 4 for positively controlled delivery of pressure gas to the closed end of the resonance tube. The length of the resonance tube corresponds approximately to one quarter of a wavelength of the sound which is to be generated in the sound generator. The sound generator is connected to pressure gas, for example compressed air, through a connector 5, and pressure gas is urged out into the resonance tube in pulses in response to a mechanically controlled valve arrangement in the sound producer, whereby the resonance tube is alternately opened and closed to the pressure gas. The mechanically controlled valve arrangement is driven by means of a drive device 5 which may be electric, hydraulic or pneumatic and which in this particular case is shown in the form of an electric motor. As a result of the mechanical control of the air pulses the frequency can be changed by the rate of the shifting of the valve arrangement between open and closed condition being increased or decreased, with the rate being matched with the wavelength of the resonance tube 1 so that optimum sound efficiency may be achieved.
The valve arrangement comprises an inlet sleeve 7 connected to the pipe connector 5, said inlet sleeve extending into the closed cylindrical housing 8 of the sound producer 4. The cylindrical housing 8 communicates with the resonance tube 1 and forms the closed end 3 thereof, with the interior of the housing comprising a portion of the interior of the resonance tube. The inlet sleeve 7 extends diametrically through the housing 8 and is disposed at an axial distance from the closed end 3. This distance is dimensioned on the basis of the circumstances in each individual case so that the best possible sound intensity in the frequency range within which the sound generator is to operate will be achieved. A valve sleeve 9 is rotatably mounted on the inlet sleeve by means of ball bearings 10, with a small gap of the magnitude of a few tenths of millimetres existing between the outside of the inlet sleeve 7 and the inside of the valve sleeve 9. In consequence of the mounting being carried out by means of ball bearings necessary lubrication can be provided without oil or grease contacting the air space. The valve sleeve is closed at one end by means of a screwed-on cover 11 and is at its other end connected to the drive flange 12 of the motor 6 by means of pins 13. The valve sleeve 9 has two diametrically opposite openings in the form of axial slits 14 for cooperation with an opening having the form of an axial slit 15 in the inlet sleeve, as is shown in Figure 3, but the valve sleeve can also have one single opening 14' for cooperation with the slit 15, as is shown in Figure 4. The sound producer has an unlimited frequency range as the latter can be selected on the one hand by the slits 14 and the slit 14', respectively, in the valve sleeve and the slit 15 in the inlet sleeve being matched with an appropriate resonator and on the other hand by the speed of the valve sleeve being regulated.
Practical tests have shown that for example boilers can be kept clean by means of frequencies up towards 400 Hz but perhaps still better with frequencies down towards 20Hz. With a correctly matched resonator infra sound far below 20Hz may be generated. No sound having intensity can be generated without a resonator but the invention permits the generation in the sound generator of sounds of high intensity and of different frequencies in the same resonator. For the mentioned frequency range from approximately 20 Hz and downwards (infra sound) it has empirically been ascertained that the slit 15 should have an area of at least 400 square millimetres, that the width (extension in the circumferential direction of the inlet sleeve 7) of the slit should not be more than 8 millimetres, and that the length (extension in the axial direction of the inlet sleeve 7) of the slit should be between 6 and 25 times the width of the slit.
As may be understood the slit 15 in the inlet sleeve 7 will be alternately opened and closed by means of the valve sleeve 9 when the latter is rotated by means of the motor 6 for delivering thrusts of compressed air to the resonance tube 1, towards the interior of which tube the slit 15 is directed.
In operation of the sound generator an air layer is located between the closed portion of the valve sleeve 9 and the inlet sleeve 7, said air layer serving as protection against friction and preventing wear as a result of the materials of the sleeves not touching each other. The layer of air also achieves cooling of the material. In order to cool the inside of the resonance tube 1 air or cooling water can be supplied to the interior of the resonance tube through a conduit 16 if desired.
In Figure 1 the sound generator is illustrated suspended in a ceiling beam 17 by means of chains or wires 18 which preferably are provided with vibration-damping members, said resonance tube 1 extending through the wall 19 to a space located outside of said wall to be kept clean by the emission of sound of low frequency (infra sound) in the space. The resonance tube should not project further into this space than that the distance to an opposite surface in front of the open end 2 of the resonance tube is at least 0,5 metres such surface being marked out by means of a dot- dash line 20. The tube connector 5 is connected to a compressed air line 21 which at least adjacent to the sound generator consists of flexible tubing connecting the sound producer to an appropriate source of compressed air (a compressor). The compressed air line 21 is provided with a cut-off valve 22, a conventional filter 23, and a magnetic valve 24, across which a narrow shunt line 25 is disposed. The magnetic valve 24 is connected to the power mains over automatic equipment 27 including a timer for opening the magnetic valve 24 at predetermined intervals which are of controllable magnitude and another timer for determining the period during which the magnetic valve is to be kept open on each occasion when it is opened. The magnitude of the last-mentioned period is also controllable. Regardless of whether the magnetic valve is open or not compressed air will pass to the sound generator through the shunt line 25, of course under the presupposition that the cut-off valve 22 is open, which it should be except when the sound generator is being serviced or it is relieved of operation for some other reason, but the flow of air through the shunt line is only a small fraction of the flow through the magnetic valve 24 when the latter is open.
The motor 6 is connected to the power mains over an adjustable regulator 27 which permits the speed of the motor to be set at a desired rate so that the frequency of the sound generated in the sound generator is governed thereby. If desired this regulator may be connected to a sensor which senses the frequency of the generated sound and adjusts the setting of the regulator for retaining the frequency of the sound at a substantially constant level.
It is appropriate to keep the motor 6 running continuously, also in the intervals between the opening periods of the magnetic valve 24, and in consequence of a flow of air being supplied to the sound generator during these intervals, although said flow of air is weak and is not sufficiently strong to generate sound in the sound generator, namely the flow of air passing through the narrow shunt line 25, the sound producer will be cooled in these intervals at the same time as its functional members are kept clean of any dust which otherwise might be distributed to the sound generator from space below the wall 19 through the resonance tube 1.

Claims

1. A sound generator for the infra sound range for regulated delivery of pressure gas pulses from a pressure gas line (7) to a resonator (1) comprising a resonance tube, the length of which substantially corresponds to one fourth of the wavelength of the sound generated in said sound generator, for keeping boilers or the like clean, characterised in that the sound generator comprises a valve member which is connected to a prime mover (6) for being driven thereby so as to control the delivery of the pressure gas pulses from the pressure gas line (7) to the resonance tube, said valve member consisting of a valve sleeve (9) which is coaxially disposed on the pressure gas line (7) and is rotatably mounted on said line by means of roller bearings (10) at each end, said valve sleeve (9) having one or more openings (14, 14') for cooperation with one or more openings (15) in the pressure gas line when the valve sleeve rotates, that a gap is disposed between the pressure gas line (7) and the valve sleeve (9) rotatably mounted thereon, that the valve sleeve (9) has an opening (14') which for achieving maximum sound intensity is dimensioned such, with regard to the openings (15) in the pressure gas line (7), that it corresponds to 50% of the opening and closing time, respectively, for producing low frequency sound, that a magnetic valve (24) controlled by timing means (26) is disposed in a line (21) for supplying gas to said pressure gas line (7) and that a shunt line (25) is connected across said magnetic valve (24) for providing a minimum air flow through the pressure gas line (7) at all times for keeping said gap free from dust.

2. A sound producer in accordance with Claim 1, characterised in that the openings (14,14'; and 15, respectively) in the valve sleeve (9) and the pressure gas line (7), respectively, are arranged as elongate slits.

3. A sound producer in accordance with Claim 2, characterised in that the slit (15) in the pressure gas line (7) has an area of at least 400 square millimetres, and that the length of the slit is from 6 to 25 times the width of the slit.

4. A sound producer in accordance with any one of Claims 1-3, characterised in that the pressure gas line (7) and the sleeve (9) mounted thereon extend diametrically in a cylindrical housing (8) which is connected to the resonator (1) and communicates with interior thereof and closes the resonator at its closed end (3).

5. A sound producer in accordance with Claim 4, characterised in that the pressure gas line (7) and the valve sleeve (9) rotatably mounted thereon are located at an axial distance from the closed end (3) of the resonator (1) formed by the housing (8).

6. A sound producer in accordance with Claim 4 or 5, characterised in that the prime mover (6) is positioned with its driving shaft connected to the valve sleeve (9) coaxial to the pressure gas line (7) and the valve sleeve (9).