GB1576210A - Detecting the level of a flowable material in a conntainer - Google Patents

Description

(54) DETECTING 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 a container comprising apparatus for sensing the level of flowable material therein, comprising a sensing head exposed at a predetermined level to the material in the container, the sensing head comprising a valve having an orifice and an obturating movable valve member, means for supplying fluid under pressure to said orifice, the valve member being arranged so as to be urged towards the orifice by the pressure of material in the container when the material is above said predetermined level, and means for detecting a change in the back pressure of the fluid supplied to the orifice resulting from the valve being open or closed.

In order that thc invention may be more clearly understood, two embodiments will now be described with reference to the accompanying drawings, wherein: Figures 1 and 2 illustrate diagrammatically alternative arrangements of a hopper and pressure system for sensing the level of material therein; and Figure 3 represents diagrammatically a suitable sensing head.

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 valve 6 controls the passage of material 2 from hopper 1 through inlet 8 to a pipe 10.

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 line 18 to a bleed-out orifice in a sensing head 37 in a side wall 22 of hopper 1. The orifice is exposed to the pressure of material in the hopper in the manner described later. When the hopper 1 is filled with flowable material 1 to a level above that of the orifice, the resistance to the flow of air through the orifice by the pressure of the material in the vicinity of and above the orifice produces a back-pressure in line 18, and in branch line 23 which leads 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 valve 6 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 valve 6 to be operated manually. 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.

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 of 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 finction 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 in 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.

In a modification shown in Figure 2, instead of a single sensing head 37, a number of sensing heads are vertically spaced apart down the side of the hopper wall. These heads 37 receive air under pressure from a common line 18. A pressure gauge 21 is provided in the line 18, either before or after the tap 30. The pressuresensitive switching arrangement of Figure 1 can also be provided in the line 18, if desired, but this is optional. The pressure in the line 18, as recorded on the gauge 21 will vary according to the number of sensing heads which are uncovered. Hence the gauge can have divisions corresponding to the various sensing heads so that the gauge reading will show how many heads 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 sensing heads provided. and this number can therefore be selected to meet the accuracy requirements.

In the embodiment of Figure 2 the position of the auge on one side or other of the taps 3v makes a difference in that, if it is upstream of the tap, the gauge will give a full hopper reading when the tap is turned offend the device 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, 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, in other situations it may be important not to overfill it.Similarly, in the embodiment of Figure 1, the tap 30 could be located upstream of the pressure-sensitive switching device, instead of downstream as shown.

A form of sensing head in shown in Figure 3. At intervals along a rigid tube 36 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 18. A compression spring 45 around the needle 41 may be provided to urge the needle away from its seating. A gauge 21 is provided in the line 18.

In use, the tube 36 can be arranged to extend down through the flowable material in the container. The flowable material bears upon the diaphragm 38 of a sensing head below the level of the material, and if the pressure of the material is sufficiently 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 back-pressures occurring in the line 18, as with the embodiment of Figure 2. 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 pressures when the material level is between two sensing heads. This embodiment is likely to be useful with liquids or other flowable materials in the container where it may be undesirable to have an orifice opening into the container 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 2. Instead of a series of sensing heads 37, a single such head is provided in the embodiment of Figure 1.

The use of a series of such sensing heads is inter alia the subject of my Patent Application No. 44204/75 (Serial No. 1576208).

WHAT I CLAIM IS: 1. A container comprising apparatus for sensing the level of flowable material therein comprising a sensing head exposed at a predetermined level to the material in the container, the sensing head comprising a valve having an orifice and an obturating movable valve member, means for supplying fluid under pressure to said orifice, the valve member being arranged so as to be urged towards the orifice by the pressure of material in the container when the material is above said predetermined level, and means for detecting a change in the back pressure of the fluid supplied to the orifice resulting from the valve being open or closed.

2. A container according to claim 1 wherein the valve member is mounted to a flexible diaphragm, one surface of which is exposed to the material in the container.

3. A container substantially as described herein with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. The use of a series of such sensing heads is inter alia the subject of my Patent Application No. 44204/75 (Serial No. 1576208). WHAT I CLAIM IS:

1. A container comprising apparatus for sensing the level of flowable material therein comprising a sensing head exposed at a predetermined level to the material in the container, the sensing head comprising a valve having an orifice and an obturating movable valve member, means for supplying fluid under pressure to said orifice, the valve member being arranged so as to be urged towards the orifice by the pressure of material in the container when the material is above said predetermined level, and means for detecting a change in the back pressure of the fluid supplied to the orifice resulting from the valve being open or closed.

2. A container according to claim 1 wherein the valve member is mounted to a flexible diaphragm, one surface of which is exposed to the material in the container.

3. A container substantially as described herein with reference to the accompanying drawings.