DE1933945A1 - Method and device for changing the cross-sectional area of a flexible neck piece of a venturi tube - Google Patents

Description

Universal Oil Products Company 30 Algonquin Road, Des Piaines, Illinois (V.St.A.)

Method and apparatus for changing the cross-sectional area of a flexible neck piece of a Venturi tube

The invention relates to a method and an apparatus for changing the cross-sectional area of a flexible venturi neck piece by reducing or changing the pressure in a space or chamber between the flexible neck and a rigid jacket which surrounds the neck and is gas-tight against the venturi is sealed. There is an evacuation to Reducing the pressure in a chamber covering the central section of the flexible neck, so that a radial inward pulling of the neck by the media flow flowing through the venturi tube is prevented.

Various devices are known for changing the cross-sectional area of a venturi neck. At a these devices are a mechanical arrangement in which a mechanical pliers device is used, to adjust the flexible walls of the throat portion of the venturi and a constant pressure drop across the inlet and to maintain the outlet of the venturi. Such a one

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Device can be operated in response to changes in the pressure differential across the venturi. As the flow of process gas through the venturi is decreased, there is less pressure differential across the venturi. In response to this change in pressure drop, the mechanical tongs can be made to narrow the walls of the venturi throat radially inward so that the cross-sectional area becomes smaller and the pressure drop across the venturi increases. If the cross-sectional area of the neck is reduced sufficiently, the pressure differential will return to its previous value. Conversely, as the process ^{gas flow increases, 1} the mechanical tongs are operated to expand the walls of the neck outwardly so that the cross-sectional area of the neck increases. A major disadvantage of such a device is that it responds only slowly and the adjustments that are brought about are imprecise and faulty when the medium flowing through the Venturi tube is compressible.

Another device that has been used to vary the cross-sectional area of a flexible venturi neck is made of an inflatable or inflatable material, which is located on the inside of the venturi neck. When the gas flow on the inlet side of the venturi decreases, the material lining the neck is inflated, thereby reducing the effective cross-sectional area of the neck. Such a one Device is particularly disadvantageous in that it - regardless of useful mode of operation when using. incompressible Media - not fulfilling its purpose or not fulfilling it sufficiently, when a compressible gas flows through the venturi or when the pressure of the compressihlen gas flow at the venturi throat. smallerν. is than the ambient pressure around the neck .:.,.> -./._

The reason for some of the difficulties encountered with conventional devices lies in the change in the Pressure that may exist inside the venturi. At the A compressible medium flows through, a venturi tube arrives.; -.

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das (Sas of a comparatively high pressure and low speed at the inlet to a comparatively low pressure and a high velocity at the outlet of the throat. It can then be seen that the pressure of the gas at the neck of the venturi can often fall below the ambient air pressure prevailing around the venturi. Furthermore, in many process systems, the venturi neck is due to the requirements in the process. operating conditions under a partial vacuum. In each prints, if the neck of the venturi is flexible, the ambient pressure - unless countermeasures are taken - the walls of the Neck radially inwards as soon as the pressure inside the neck is smaller than the surrounding external pressure. When this happens changes in flow rate and inlet pressure cause changes in the cross-sectional area of the throat and thus changes also changes in the pressure differential between the inlet and the Venturi outlet. It was found that by one, multiple and reliable control means the walls of the neck portion pushed outwards or adjusted accordingly and thus the desired constant pressure drop across Venturi tube can be maintained .. This is achieved in a satisfactory manner by the method and the device according to the invention,. . = '. ■; .--.

The main object of the invention is thus to provide a method and an apparatus which are capable of bringing about the necessary changes in the cross-sectional area of the neck of a venturi to maintain a constant desired pressure differential across the venturi at different process gas flow rates. In connection with this, the invention also aims to provide a method and a device which respond more quickly and more precisely than conventional systems to changes in flow in the Venturi tube. , -, · _; , ■ - -., -: ., · .- ■ -----. ■ - .: ■ .. ";,:. - ._ ■ - - \ ■ '·" -

"" "The invention is applicable in numerous areas. An important area of application are venturi scrubbers for cleaning

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of particle-laden gases. In such scrubbers a gas stream, the dust particles and water is atomized contains, passed through a venturi, chen the partial agglomeration of the '] support. In such a case, the desired pressure difference across the Venturi tube must be kept constant even with changes in the inlet pressure or the flow rate. Such devices are used wherever undesired particles are to be removed from a gas stream. Another application is in fuel delivery systems for internal combustion engines. Special applications of this type are found in astronautical as well as land , air and water vehicles or apparatus in which combustion engines are used for propulsion. Further applications are, for example, devices for heating natural gas, suction cleaning devices, gas burners, fuel gas torches ", etc.

According to the invention is thereafter a method for Changing the cross-sectional area of a flexible neck piece a Venturi tube provided, which is characterized is to sense the pressure drop across the venturi and a gas-tight chamber surrounding a flexible neck piece as required and evacuated in response to the sensed pressure drop.

Further according to the invention is an apparatus provided for changing the cross-sectional area of a flexible neck piece of a Venturi tube, which is marked by

a) a rigid jacket surrounding the neck and a delimits the gas-tight chamber surrounding the neck piece,

b) a vacuum source,

c) a valve device which is connected to the vacuum source and a gas flow channel coming from the gas-tight chamber and is constructed and arranged so that the gas-tight chamber is exposed to the action of the vacuum source to a variable extent in response to a control signal,

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d) a differential pressure sensing device connected to the inlet and is connected to the outlet of the venturi, and

e) a differential pressure regulator that works with the differential pressure sensing device and the valve device connected and so is designed and arranged that the control signal is generated in accordance with the pressure difference prevailing at the Venturi tube.

Changing the cross-sectional area of the throat of the venturi in response to changes in the pressure differential across the venturi results in the maintenance of a desired pressure differential as the process gas flow rates change. On the basis of the principles of fluid mechanics it can be shown that the pressure changes inversely with the velocity when a gas flows through a venturi. Since the speed at the neck of the venturi will always be greater than the speed at the inlet, the pressure of the gas flow at the neck is always lower than the pressure at the inlet of the venturi. If the gas stream is initially at a comparatively low pressure, ie an inlet pressure only slightly above atmospheric pressure, the pressure at the throat will often drop below atmospheric pressure. The negative pressure generated in this way, when it is acted unrestrictedly, causes the central portion of the flexible neck to be pressed radially inward by the ambient atmospheric pressure prevailing around the flexible neck. Subsequent increases in gas flow at the inlet tend to further decrease the pressure at the throat and increase the resulting pressure drop from inlet to outlet. Atmospheric pressure therefore tends to further close the flexible throat. Subsequent decreases in gas flow at the inlet tend to be to increase the pressure at the neck and reduce the resulting pressure drop from the inlet to the outlet. The increased pressure "on the neck" in this case tends to press the central part of the flexible " neck" e-twä * o ~ radially outward. In either case, the pressure drop changes from inlet to outlet.

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what is desired is the pressure drop from inlet to outlet with changes To maintain the flow conditions at a predetermined level, this can be achieved in a satisfactory manner by controlling the enlargement and constriction of the neck by the method and the device according to the invention.

The structural design and mode of operation of the valve no device and the differential pressure transmitter according to the invention can be made according to various embodiments. Each of these facilities can operate in different ways This includes, for example, but not limited to, actuation by electrical means., with spring preload, pneumatic operation or any combination ■ tion of it. Any conceivable structural configurations of these devices in connection with one another can be used to be used. The preferred embodiments of the invention comprise either a pressure differential transmitter, the sends out an electrical signal to adjust the valve device, or a pressure differential transmitter that sends a pneumatic Emits signal for setting the valve device.

The venturi is usually symmetrical around one straight axis formed. For some applications the Ge; stalt of the Venturi tube can also be modified and the Axis around which the individual parts of the, ■ Venturi tube are arranged, have a curve shape of a less common type. .; -

The invention and its various features will be further below in connection with the attached drawing illustrated. The drawing shows a vertical Section through a preferred embodiment of the invention.

: A Venturi tube 23 comprises an inlet piece 2, a flexible one; Neck piece 1, for example made of rubber ^ and eixi'Äuslaßstück 3. The neck piece 1 can not only consist of rubber but generally of any suitable elastic material.

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let 2, the neck 1 and the outlet 3 are in the illustrated Embodiment arranged on a common axis. The flexible one Neck 1 is at its inlet end 32 on the entire circumference the connection with the. adjacent portion of the inlet piece 2 sealed against the latter, its outlet end 34 is correspondingly on the entire perimeter against the adjacent section of the Outlet piece 3 sealed. The middle section 33 of the neck piece is well flexible and thus radially movable with respect to the Central axis of the venturi. In the illustrated embodiment, the pressure is at point "a", i.e. a point in the inlet piece 2, through a connecting leg '24 to a pressure gauge 5 transfer. From point "c", i.e. a point in outlet piece 3, the pressure is transmitted to the pressure gauge 5 through a connecting leg 25. A point "b" is drawn in that it is in the the narrowest part of the flexible neck 1 lies.

A jacket 4 made of steel or any other impermeable material that is more rigid or stiffer than the neck 1, surrounds the neck 1 and has a gas-tight passage opening for the Venturi tube 23 to both ends of the neck 1. The jacket 4 thus encloses these passage openings the inlet piece 2 and the outlet piece 3 and is sealed against it. A connecting pipe 9 connects the chamber formed within the jacket 4 to a valve device 11. The valve device 11 is in turn connected by a line 12 to a not shown. Vacuum source V connected. The valve device 11 is designed so that it is a suction of gas, usually Air, to the vacuum source from the chamber within the Jacket 4 through the connecting pipe 9 and / or from the environment, usually the atmosphere, through a line 10. the Valve means 11, 11 can thus be controlled in such a way that it either communicates with the atmosphere or the chamber or with the vacuum source connects.

In the preferred embodiment, the valve means comprises 11 an enclosing housing wall 27 in which there is a connection opening for the line 12 leading to the vacuum source

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V leads is located. This air passage remains during all drive phases open. There is also a connection opening for the Line 10, which leads to the atmosphere, and a connection opening for the connecting pipe 9 leading to the chamber in the jacket 4 leads, provided. In the valve device there is a Gasflussab'sperrarm 13 which is rotatably mounted about a pin 26 so that it is in positions of full or partial Blockage of the air flow through line 10 can be brought about. The valve device 11 further comprises an elongated one inflatable hose or bag 14, which is attached to the shut-off arm 13

fe is attached or it abuts, a spring 16, which endeavors - is> to pull the Absperrarm 13 from the line 10, and a connecting line 15 which is connected to the inflatable tube 14 and leads to a pressure difference transmitter 17th When air under pressure from the differential pressure transmitter 17 enters through the connecting line 15, the hose 14 is inflated and thus has the tendency to stretch out from its folded or slack state in its longitudinal direction, whereby a pivoting of the shut-off arm 13 about the pivot point 26 away from the Connecting pipe 9 and is brought about in front of the opening of the line. If no air pressure is given from the pressure differential transmitter 17 to the connecting line 15, the inflated hose 14 loses pressure backwards through the

fc connecting line 15, so that the hose 14 again its non-inflated Position and the spring 16 the shut-off arm pulls away from line 10. _,

The differential pressure transmitter 17 is operated and comprised independently with a compressed air source D (not shown) a rigid enclosing housing wall 30 with an opening to it the connecting line 15; in the housing wall 30 is located a pressure relief valve 29, inlet air supply pipe 22 connected to the Compressed air source is connected, enters through an opening the housing wall 30 and is sealed gas-tight against this wall, the same applies to the connecting line 15 * a part

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of the air supply pipe 22 extends into the pressure differential transmitter 17 and in this part of the pipe 22 there is an electromagnetic relay 18 which, when energy is supplied, a spring clip. 19 draws towards himself. The spring clip 19 is fixedly attached to the air supply tube 22, for example by a weld 28. A needle valve 20 is attached to the spring clip 19 which _: engages in a valve seat 21 which forms the end of the air supply tube 2 2 or is located therein. The electromagnetic relay 18 is designed to be strong enough to overcome the pressure of the compressed air supplied through the pipe 22 and to pull the spring clip 19 upwards as soon as it is excited by an electrical current which is supplied by a battery via insulated electrical wire conductors 7 and 8 is fed; the latter lead through the housing wall 30 and the air supply pipe 22 and are sealed against it. Upon actuation of the electromagnetic relay 18 of the spring clip 19 is pulled up, the needle valve 20 lifts off the valve seat 21 and it can compressed air into the of the housing wall 30 enclosed space and the connection line 15 occur, so that the valve device is actuated. 11 When the electromagnetic relay is no longer fed, the spring clip 19 returns to its normal position, so that the needle valve 20 is seated in the valve seat 21 again. The pressure in the connecting line 15 is released through the pressure relief valve 29, which allows air to escape slowly into the atmosphere when the needle valve 20 is closed. The pressure relief valve 29 is only so large that it does not cause any significant impairment of the pressure transmitted to the connecting line 15 when the needle valve 20 is open. .

The electromagnetic relay 18 is actuated by a ¹ battery when contacts "d" and "e" in a leg 'of the pressure gauge. 5: * connecting to the connection leg 25 ", - are closed, the contacts d and e are closed when the pressure difference between the inlet piece 2 and the outer

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Let piece 3 of the Venturi tube 23 rises so far that the mercury 6 in the manometer 5 to the height of the contacts d and e in the leg 25 can rise. In the leg 25 are a number of copper wires arranged in pairs, which extend through the wall at different predetermined heights. The contact d, which is connected to the wire 31, is attached to one of the paired copper wires at the desired height. The contact d is after attachment to one of the paired copper wires via the wire conductors 31 and 7 with one pole of the electromagnetic relay 18 connected. The contact e is fe on the other of the paired copper wires in the desired Fixed altitude and is about the wire conductor 8 with the other Pole of the relay connected so that the circuit is closed. If the mercury is 6 to -to the height of the chosen copper wire pair increases, the electrical circuit from the battery through the wire 7 to the electromagnetic relay 18, through the wire 8 to the contact e, through which of the mercury 6 connected copper wire pair to contact d and then through the Wire 31 closed back to the battery.

As explained above, when the pressure at point a increases, the pressure drop tends to increase between points a and c and a decrease in | Pressure at point b, i.e. narrowing the opening of the neck 1. However, such a process is prevented by the method and the device according to the invention. If the If the pressure between points a and c rises, the level of mercury 6 in the connecting leg 25 also rises leading leg of the pressure gauge 5 and thereby closes the Contacts of the electrical circuit, resulting in a feed 'of the electromagnetic. Rel; ai & 18 - leadsC; -The · electromagnetic Relay 18 pulls-then the. ; Efede-rfeügel ^ -l-9 · southward, causing the needle valve 20 from my 'Si ^^^ b ^ hoto ^ n'iwilrd and compressed air from> the source of compressed air: via the 'flow supply 22' into the ' Dru-ckd if ferenzühert rager 17 And then ^ düzjch'-the line; IFzIi the Valve device 11 arrives. The pressurized air in.

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the connecting line 15 pumps up the hose 14- and presses as a result, the shut-off arm 13 in front of the line 10. The vacuum source V connected to the valve device 11 thus sucks Air from the space enclosed by the rigid jacket 4 and thus equalizes the pressure between this space and the pressure in the valve neck at point b. With equal pressure the flexible neck 1 no longer tends to narrow. When the space enclosed by the rigid jacket is sufficiently evacuated, the pressure drop reaches from point a to Point c again the desired height and the electrical contact through the mercury 6 is broken. When this occurs, results The same happens in the device shown as with a decrease in pressure at point a.

• When the pressure, and consequently the speed, is on Drop point a, there is a tendency for a decrease in the pressure difference between points a and c and an increase in the Pressure at point b, i.e. to widen the opening of the Neck 1. Such a process is avoided by the method and the device according to the invention. If the If the pressure is between points a and e, the level of mercury falls 6 in the leg leading to the connecting leg 2 5 of the pressure gauge -5 so that the contacts d and e of the electrical Open the circuit for the supply of the electromagnetic relay 1.8. The electromagnetic relay 18 is thus the Spring clip 19 free and this returns to its normal position, whereby the needle valve 20 closes and prevents Compressed air from the compressed air source through the air supply line, 2-2 in. The ones under pressure stagnant air, which * previously inflated the hose 14, can through the pressure relief valve 2 9, and the spring 16 pulls the shut-off arm 13 away from the line 10. Analogously, it sucks the valve device 11 connected vacuum source in a correspondingly large amount of air from the atmosphere through the line.10 on ,, instead of suction from that of the solid jacket. %around-

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given chamber. The resulting increase in pressure in the Inside the chamber, which of the jacket 4, the inlet piece 2, the Ausläßstück 3 and the flexible neck 1 made of rubber or the like. limited if j causes a radial inward pushing of the middle section ' 3 3 of the flexible neck 1, whereby the pressure drop increases from point a to point c, until this pressure drop is the desired level achieved. If the pressure difference between a and c is too great increases, the same results in the device shown as in the case of the previously explained increase in the pressure at point a.

The following example is provided for further illustration the invention.

• Example

A flexible neck of a venturi tube of variable cross-sectional area with a radially movable central part was surrounded by a rigid jacket "which was hermetically sealed against the venturi tube on both sides of the neck." ■■ ·.

The nominal cross-sectional area of the neck was a Quarter of that of both the inlet and the outlet. It Air flowed through the Venturi tube at a speed of about 60 m / sec, the density of this air was 1.44 kg / m. Under under these conditions the pressure drop between the inlets was and the outlet of the venturi about 38.1 mm of water and the throat pressure was below atmospheric pressure. Upon acceptance of the Inlet gas flow, with a concomitant decrease in gas * speed, became - as explained - a tendency to decrease also the pressure difference between the inlet and outlet and observed the increase in pressure on the neck. However, this tendency could be easily overcome by applying the invention by sensing the pressure prevailing on the venturi Pressure difference and reduction in the degree of evacuation of the

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Space between the rigid jacket and the Venturi tube in accordance with and in response to the pressure difference decrease over the venturi. The pressure within the enclosed space was kept higher in this way by partially allowing atmospheric pressure and thereby a radial expansion of the neck to the outside. . .

When the gas flow rate increased again, as explained, a tendency to increase the pressure drop observed between the inlet and the outlet and to further close the throat. By evacuating the room more strongly around the neck according to and in response to the increase in the pressure difference across the venturi, however, the Neck properly prevented from such a narrowing and thus the pressure drop between the inlet and the outlet can be maintained.

Claims (1)

Claims Method for changing the .querschpitt.sfJ.äqh.e of a flexible neck piece of a Venturi tube, marked by dadureX ;. _l __ characterized in that senses the pressure drop across the _venturi. . and a gas-tight surrounding the flexible neck piece. Chamber after. Evacuated in response to the sensed pressure drop. - - - - '■ 2. Device for changing the cross-sectional area. before a flexible neck piece of a venturi tube, characterized by. '-' ■ χ a limited) a rigid casing ⁽¹ O, of the throat (1) surrounds the throat and a surrounding gas-tight chamber, b) a vacuum source (V), c) a valve device (11) connected to the vacuum source and a gas flow channel coming from the gas-tight chamber (Connection pipe 9) is connected and so designed and arranged that it changes the gas-tight chamber • Measures in response to a control signal of the action of the The vacuum source fails, d) a differential pressure sensing device (24- _s 25, 5) which is connected to: the inlet (2) and the outlet (3) of the venturi tube (23); and i V- e) a differential pressure regulator (17) which is connected to the differential ^{pressure discharge device (2 ι} Γ, 25, 5) and the valves (11) and is designed and arranged so that the control signal depends on the pressure difference prevailing at the venturi tube (23) is produced. 3i device according to claim 2 ^ thereby kehnÄeiehnet, that the control signal is an electrical signal * 4. Apparatus according to claim 2! <, dadürdh gekerinzeichhet, that the control signal is a pneumatic Sigiiai Γ 0 9 8 8 4 / Ö ill BAD ORIGINAL 5. Device according to one of claims 1-4, characterized characterized in that the valve device (11) has an outlet (10) to the atmosphere (A) which is so constructed and arranged is that he is adjustable in the manufacture -. a connection between the vacuum source (V) and the atmosphere (A) permitted. 6. Device according to one of claims 1-5, since characterized in that the flexible neck (1) of the Venturi tube (23) consists of rubber. 90988 4/0402 Read more