GB1576208A

GB1576208A - Sensing the level of a flowable material in a container

Info

Publication number: GB1576208A
Application number: GB4420475A
Authority: GB
Original assignee: Barton W B
Current assignee: Barton W B
Priority date: 1975-10-27
Filing date: 1975-10-27
Publication date: 1980-10-01

Description

(54) SENSING THE LEVEL OF A FLOWABLE MATERIAL IN A CONTAINER (71) I, WILFRED BRIAN BARTON, of St. David's Cottage, Codrington, Chipping Sodbury, Bristol, a British Subject, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to sensing the level of a flowable material in a container, The present invention provides in one aspect a method for sensing the level of flowable material in a container, which comprises: applying a fluid under pressure from a common supply to a series of orifices which are exposed at different levels with respect to the container to the pressure of said material above their respective levels such that said pressure of material opposes the escape of fluid through the orifices below the level of material, and sensing the overall resistance to the flow of fluid through the orifices by detecting consequent variations in the back-pressure of the fluid in the supply to the orifices caused by variations of the level of material in the container.

Thus, if the orifices open directly into the container and the fluid is directed under pressure along the supply line towards the orifices, then the fSowable material disposed in the vicinity of or above an orifice offers a resistance to the flow of fluid through that orifice, which resistance manifests itself in an increased back-pressure produced in the flow line which back-pressure can be sensed by conventional means. Instead of opening directly into the container, each orifice may be part of a valve and is obturated by a valve member which is urged towards the orifice by said pressure of material.

The back-pressure can be caused to operate a device for controlling the passage of flowable material into or out of the container so that when the level of material in the container falls below or rises above a predetermined desired level, the supply of material to or passage of material from the container is adjusted to bring the level of material back to the desired level.

The present invention in another aspect provides a container with apparatus for sensing the level of flowable material therein in the manner described above.

The back-pressure preferably operates a pressure-sensitive switch which can be used to control any desired function, for example a valve at the outlet of the container.

The fluid is preferably air, suitably at a pressure of 0 - 10 psig, for example 6 psig.

In order that the invention may be more clearly understood, two embodiments will now be described with reference to the accompanying drawings, wherein: Figure 1 illustrates diagrammatically one arrangement of a hopper and pressure system for sensing the level of material therein; and Figure 2 represents diagrammatically part of another embodiment suitable for sensing liquid levels.

Referring to Figure 1; a hopper 1 contains flowable material 2, such as grain or powder at a level 4. Means (not shown) are provided for supplying material 2 to hopper 1 and an outlet valve controls the passage of material 2 from hopper 1 to a pipe.

High pressure air is supplied along a line 12 at a pressure of, for example 100 psig from a conventional industrial air supply, through a filter 14 and thence to an adjustable pressure reducer 16, where the air pressure is reduced to, for example 6 psig.

The air at 6 psig is then supplied along a common supply line 18 to a series of bleed-our orifices 20 vertically spaced apart down a side wall of hopper 1. A tap 30 can be provided in line 18 so that the air supply to the hopper can be switched off when the hopper is not in use.

When the hopper 1 is filled with flowable material 2 to a level above that of an orifice 20, the resistance to the flow of air through that orifice by the material in the vicinity of and above the orifice produces a backpressure in line 18, and this can be detected, for example, by a pressure gauge 21, or a pressure sensitive switching arrangement.

Such a switching arrangement, if provided, may take the form of a branch line 23 from the line 18 leading to a pressure-sensitive switch 24 in, for example a high pressure air supply line 25. When the back-pressure drops below a predetermined value, indicating that the material level in the hopper is below a predetermined level, the switch 24 operates to allow high pressure air from a supply line 25 (which can be a branch from line 12) to flow through line 26 to a high pressure switch 28. The switch 28 may operate means (not shown) for controlling the supply of material to the hopper. Alternatively or additionally, however, switch 28 can be set to operate the outlet valve to control flow of material from the hopper.

As a further alternative, switch 28 can merely operate an alarm for the material supply means of the outlet valve to be operated manually.

Alternatively, the level sensing device, or an additional level sensing device, can be arranged so as to prevent overfilling of the container by detecting a predetermined upper limit to the material level and controlling the material supply accordingly.

The valve 24 can be an air valve having a spring-loaded valve member held in one condition against the spring by a preset low pressure in line 23 or say 5 psig, so that when the pressure in lines 18 and 23 decreases to this value, valve 24 changes to the other condition, thus affecting the supply of air to line 26 and switch 28.

Alternatively, switch 24 may be a proximity switch, for example having a diaphragm or hinged flap which forms one plate of an electrical capacitance, the movement of the flap or diaphragm under varying air pressure causing a variation in capacitance which is detected at the other, fixed, plate, and operates an electronic switching circuit when the capacitance exceeds a predetermined value. The switching circuit can be used directly to control the desired function so that the lines 25, 26 and switch 28 can be dispensed with.

Another form of switch uses a plunger in a tube exposed to the pressure of the air line. The plunger could be a slidable sealing fit in the tube and be moved by the air pressure against a light spring. Alternatively, the plunger could be located in a tapering tube, or a tube with an enlarged internal diameter or leak opening at one point, whereby the air pressure will move the plunger to a point at which the leakage of air past the plunger relieves the pressure to an extent which prevents further movement of the plunger. The plunger, if made of a magnetic material, could operate a magnetic reed switch for control purposes as described above.

If a pressure gauge 21 is provided it can be located in the line 18 either before or after the tap 30. The pressure in the line 18, as recorded on the gauge 21, will vary according to the number of orifices 20 which are uncovered. Hence the gauge can have divisions corresponding to the various orifices, so that the gauge reading will show how many orifices are uncovered, and hence the approximate level of the material in the hopper. The accuracy of this- method of determining the level will depend on the number of orifices provided, and this number can therefore be selected to meet the accuracy requirements. The gauge reading will tend to give some indication of the level of the material between two orifices as a result of the resistance provided by the material to the leakage of air from a covered orifice.However, the height of material above a covered orifice will vary for a given gauge reading according to the density and nature of the material, so that the reading is only qualitative unless the gauge is cablibrated for the particular material. The device provides however a definite indication of the material level within known limits. The position of the gauge on one side or other of the tap 30 makes a different in that, if it is upstream of the tap, the gauge will give a full hopper reading when the tap is turned off and the device is not functioning, whereas if the gauge is downstream of the tap it will read empty when the tap is turned off.Since a failure of the gas supply will be equivalent to turning off the tap, since there willthen be no supply to the orifices, the gauge position can be selected according to whichever of these gauge conditions is preferred for a particular installation. For example in some situations, it may be important not to let the hopper become empty so the gauge is located downstream of the tap; in other situations it may be important not to overfill it, so the gauge is located upstream of the tap. Similarly the pressure-sensitive switching device could be located downstream of the tap instead of upstream as shown.

Provision may also be made for cleaning the orifices 20. In the arrangement of Figure 1, this can be achieved by means of a high pressure by-pass line 31 which supplies high pressure air to the orifices 20 to clear any blockages. A tap 32 is being linked with the tap 30, for example mechanically, or electrically through operating solenoids, so that when the tap 32 is opened the tap 30 is closed, thereby preventing high pressure air from being connected with the low pressure switches 24, 28. However, if the gauge 21 is located after the tap 30, an isolating tap 33, also linked with the tap 32, will be required to prevent its being exposed to high pressure. Separate independently operable valves 34 may be provided with each orifice 20 so that, during cleaning, one orifice at a time can be opened, thereby ensuring that each orifice is exposed to the maximum available pressure.Removable caps 35 may additionally or alternatively be provided at the ends of the short branch lines leading to the orifices 20, so that a cap can be removed and a cleaning instrument inserted along the line and into the orifice 20.

As a modification, hinged flaps may be located over the inner ends of the orifices where they open into the container. This would give a more positive open/closed effect, and would also lessen the risk of blockage of the orifice by the material.

Figure 2 shows a modification of the invention which does not require air to escape into the flowable material. A rigid tube 36 extends down through the flowable material. At intervals along the tube a number of sensing heads 37 are located (only one is shown in the drawing). Each sensing head comprises a flexible diaphragm 38 sealed across an opening in the wall of the tube. A chamber 39 is provided behind the diaphragm, the various chambers being interconnected by a conduit 40 which vents to air at the top end of the tube 36. Within the chamber 39 is a valve provided by a needle 41 mounted to the centre of the diaphragm which co-operates with a valve seating 42 at the end of a branch line 43 leading from a common low pressure air line 44 (similar to the line 18 in Figure 1). A compression spring 45 around the needle 41 may be provided to urge the needle away from its seating.A gauge 46 (similar to the gauge 21 in Figure 1) is provided in the line 44.

In use, the flowable material bears upon the diaphragm 38, and if its pressure is sufficently great it will close the needle valve in the chamber 39. If the pressure is insufficient the valve will be open and air will leak out to atmosphere through the conduit 40. These two situations will be reflected by different pressures occurring in the line 44, as with the embodiment of Figure 1. The device can thus be arranged to indicate the approximate level of the flowable material. If the needle or the orifice is tapered the resistance to the flow of air through the orifice will vary over a range of positions of the needle, and thus will produce useful intermediate pressure when the material level is between two sensing heads.

This embodiment is likely to be more useful with liquids or other flowable materials where it may be undesirable to have an open orifice or the continuous flow of air through the material.

The tube 36 could be omitted and the arrangement of sensing heads and air lines and conduits left in skeletal form, either mounted inside the container or mounted externally to the wall of the container, as in Figure 1. Likewise the embodiment of Figure 1 could be constructed as a selfcontained unit for insertion into the flowable material in an existing container.

The pressure sensing head of Figure 2 forms the subject of dimensional patent application No. 22069/79 (Serial No.

1576210), and the orifice cleaning arrangement of Figure 1 forms the subject of dimensional patent application No. 22068/ 79 (Serial No. 1576209).

WHAT I CLAIM IS: 1. A method for sensing the level of flowable material in a container, which comprises: applying a fluid under pressure from a common supply to a series of orifices which are exposed at different levels with respect to the container to the pressure of said material above their respective levels such that said pressure of material opposes the escape of fluid through the orifices below the level of material, and sensing the overall resistance to the flow of fluid through the orifices by detecting consequent variations in the back-pressure of the fluid in the supply to the orifices caused by variations of the level of material in the container.

2. A method according to claim 1, wherein the orifices open into the container at said predetermined levels, so that the fluid escaping from an orifice flows through the material in the container if the level of material is above the level of the orifice.

3. A method according to claim 2 wherein the fluid is supplied from a relatively high pressure source and the pressure is reduced before applying it to the orifices.

4. A method according to claim 3 wherein a by-pass is provided from said high pressure source so that, when required, high pressure fluid can be applied directly to the orifices to assist in clearing them.

5. A method according to claim 1 wherein said orifice is part of a valve, and is obturated by a movable valve member which is urged towards the orifice by said pressure of material.

6. A method according to claim 5 wherein the valve member is connected to a flexible diaphragm which is exposed on one surface to the material in the container.

7. A method according to any one of the preceding claims wherein the variations in pressure of the fluid resulting from the

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Claims

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when the tap 32 is opened the tap 30 is closed, thereby preventing high pressure air from being connected with the low pressure switches 24, 28. However, if the gauge 21 is located after the tap 30, an isolating tap 33, also linked with the tap 32, will be required to prevent its being exposed to high pressure. Separate independently operable valves 34 may be provided with each orifice 20 so that, during cleaning, one orifice at a time can be opened, thereby ensuring that each orifice is exposed to the maximum available pressure. Removable caps 35 may additionally or alternatively be provided at the ends of the short branch lines leading to the orifices 20, so that a cap can be removed and a cleaning instrument inserted along the line and into the orifice 20.

As a modification, hinged flaps may be located over the inner ends of the orifices where they open into the container. This would give a more positive open/closed effect, and would also lessen the risk of blockage of the orifice by the material.

Figure 2 shows a modification of the invention which does not require air to escape into the flowable material. A rigid tube 36 extends down through the flowable material. At intervals along the tube a number of sensing heads 37 are located (only one is shown in the drawing). Each sensing head comprises a flexible diaphragm 38 sealed across an opening in the wall of the tube. A chamber 39 is provided behind the diaphragm, the various chambers being interconnected by a conduit 40 which vents to air at the top end of the tube 36. Within the chamber 39 is a valve provided by a needle 41 mounted to the centre of the diaphragm which co-operates with a valve seating 42 at the end of a branch line 43 leading from a common low pressure air line 44 (similar to the line 18 in Figure 1). A compression spring 45 around the needle 41 may be provided to urge the needle away from its seating.A gauge 46 (similar to the gauge 21 in Figure 1) is provided in the line 44.

In use, the flowable material bears upon the diaphragm 38, and if its pressure is sufficently great it will close the needle valve in the chamber 39. If the pressure is insufficient the valve will be open and air will leak out to atmosphere through the conduit 40. These two situations will be reflected by different pressures occurring in the line 44, as with the embodiment of Figure 1. The device can thus be arranged to indicate the approximate level of the flowable material. If the needle or the orifice is tapered the resistance to the flow of air through the orifice will vary over a range of positions of the needle, and thus will produce useful intermediate pressure when the material level is between two sensing heads.

This embodiment is likely to be more useful with liquids or other flowable materials where it may be undesirable to have an open orifice or the continuous flow of air through the material.

The tube 36 could be omitted and the arrangement of sensing heads and air lines and conduits left in skeletal form, either mounted inside the container or mounted externally to the wall of the container, as in Figure 1. Likewise the embodiment of Figure 1 could be constructed as a selfcontained unit for insertion into the flowable material in an existing container.

The pressure sensing head of Figure 2 forms the subject of dimensional patent application No. 22069/79 (Serial No.

1576210), and the orifice cleaning arrangement of Figure 1 forms the subject of dimensional patent application No. 22068/ 79 (Serial No. 1576209).

WHAT I CLAIM IS: 1. A method for sensing the level of flowable material in a container, which comprises: applying a fluid under pressure from a common supply to a series of orifices which are exposed at different levels with respect to the container to the pressure of said material above their respective levels such that said pressure of material opposes the escape of fluid through the orifices below the level of material, and sensing the overall resistance to the flow of fluid through the orifices by detecting consequent variations in the back-pressure of the fluid in the supply to the orifices caused by variations of the level of material in the container.

2. A method according to claim 1, wherein the orifices open into the container at said predetermined levels, so that the fluid escaping from an orifice flows through the material in the container if the level of material is above the level of the orifice.

3. A method according to claim 2 wherein the fluid is supplied from a relatively high pressure source and the pressure is reduced before applying it to the orifices.

4. A method according to claim 3 wherein a by-pass is provided from said high pressure source so that, when required, high pressure fluid can be applied directly to the orifices to assist in clearing them.

5. A method according to claim 1 wherein said orifice is part of a valve, and is obturated by a movable valve member which is urged towards the orifice by said pressure of material.

6. A method according to claim 5 wherein the valve member is connected to a flexible diaphragm which is exposed on one surface to the material in the container.

7. A method according to any one of the preceding claims wherein the variations in pressure of the fluid resulting from the

resistance to flow through said orifices is used to operate a signal or to control charging of material into or discharging of material from the container when the level of material is below or above a predetermined level.

8. A method for sensing the level of flowable material in a container, substantially as described herein with reference to Figure 1 of the accompanying drawings.

9. A method for sensing the level of flowable material in a container, substantially as described herein with reference to Figure 2 of the accompanying drawings.

10. A container comprising apparatus for sensing the level of flowable material therein, comprising a common supply line supplying fluid under pressure to a series of orifices exposed at different levels with respect to the container to the pressure of material above their respective levels, and means for detecting variations in the backpressure of said fluid in the supply line to the orifices resulting from variations in overall resistance provided by said material to the escape of fluid through the orifices.

11. Container according to claim 10 wherein the orifices open into the container at said predetermined levels, so that the fluid escaping from an orifice flows through the material in the container if the level of material is above the level of the orifice.

12. Container according to claim 10 or claim 11 wherein said common supply line includes a fluid supply conduit mounted substantially upright within the container a plurality of said orifices being spaced apart along the conduit.

13. Container according to claim 11 or claim 12 including means for reducing a relatively high pressure source of said fluid to a lower pressure for supply to said orifices.

14. Container according to claim 13 including a controllable by-pass line for supplying high pressure fluid directly to said orifices when required.

14. Container according to claim 10 including a plurality of sensing heads exposed at said predetermined levels to the material in the container, each sensing head comprising a valve having a said orifice and obturating movable valve member, the valve member being arranged so as to be urged towards the orifice against the flow of said fluid therethrough by the pressure of material in the container when the material is above its respective level.

16. Container according to claim 15 wherein each valve member is mounted to a flexible diaphragm, one surface of which is exposed to the material in the container.

17. Container according to claim 16 wherein the sensing heads are carried by an elongate tube, a number of apertures being provided in the wall of the tube corresponding to the number of sensing heads, at which apertures the movable valve members are exposed to the pressure of material in the container.

18. Container according to any one of claims 10 to 17 including a device responsive to said variations of fluid pressure for operating a signal or controlling charging of material into or discharging of material from the container when the level of material is below or above a predetermined level.