GB2162316A - Liquid level sensing systems - Google Patents

Abstract

A liquid level sensing system employs a tube 2 which is used to draw liquid from a container through an opening 4, near the lower end of the tube. A float valve 1,7, partially seals the opening in the tube when the liquid in the container has dropped to a predetermined level and the resulting reduction in flow rate is sensed by a remote flow rate sensor. <IMAGE>

Description

SPECIFICATION Liquid level sensing systems The present invention relates to devices for controlling liquid flow rates and to systems employing such devices for detecting liquid levels in a container.

When drawing liquids from containers it is frequently necessary to determine when the container is empty or nearly empty. This can be done by fitting float switches, conductivity probes or other level sensors, however this is not very convenient when drawing liquids from disposable containers such as plastic bottles.

According to the invention a liquid level and flow rate sensing system comprises a tube or the like insertable within a vessel and serving to draw liquid from the vessel via an opening in the tube, or valve adapted to partially seal the opening when the level of the liquid falls to a predetermind level to reduce the flow rate through the tube and a flow rate sensor for sensing when the flow rate is reduced.

The valve which acts as a liquid level and flow rate controller can take a variety of forms. For example a sleeve carrying a float may move along the tube or a spherical float can be constrained to move in relation to the opening. The valve seals, or partially seals, the tube when the liquid level falls to near the level of the float.

If advance warning of the container emptying is required, the valve is arranged to only partially seal the tube, so that liquid can continue to be drawn out of the container.

Alternatively the valve can be arranged completely to seal the tube, thus acting as a shutoff valve which stops air being drawn into the system.

The effect of sealing or partially sealing the tube will be to shut off or reduce the flow of liquid through the tube and the sensor, which can sense this remotely can provide a signal indicating that the vessel is nearly empty.

Specific embodiments of the invention will now be described by way of examples with reference to the accompanying drawings; in which: Figure 1 is a sectional side view of one embodiment of a controller device constructed in accordance with the invention mounted in a typical container.

Figures 2 to 4 depict the device shown in Fig. 1 with the container contents at different levels.

Figure 5 depicts the device shown in Fig. 1 with the float thereof in a different position.

Figures 6A and 6B are elevational and sectional plan views of another embodiment of a controller device constructed in accordance with the invention.

Figures 7 and 8 are side views of the device shown in Figs. 6A and 6B with the container contents at different levels.

Figure 9 is a block schematic diagram depicting a liquid level and flow rate sensing system constructed in accordance with the invention.

Referring initially to Fig. 9, a liquid level and flow rate sensing system is associated with a vessel or container 5 containing liquid which is dispensed therefrom. A controller device 20 serves to extract liquid from the container 5 by suction through the tube 2 for example, and the liquid passes along a flow path 22. The flow rate of liquid along the path is controlled in accordance with the level 9 of the liquid in the container 5 so that the lower the level and the less liquid stored, the lower the flow rate. A flow rate sensor 21 monitors the flow rate and provides a signal or indication when this signifies that the vessel 5 is nearly empty.

Referring now to Fig. 1, a liquid level and flow rate controller 20 for use in the system is in the form of a float valve comprising a sleeve 1 sliding on a tube 2. The lower end of the tube 2 is covered with a blanking plug 3 and an opening 4 in the tube 2 allows liquid to be drawn into the tube 2. The tube 2 is mounted and retained in the container 5 by a cap 6. Attached to the sleeve 1 is a float 7 which is small enough to pass through the neck 8 of the container 5. The height of the lower part of the sleeve 1, can be set relative to the liquid level 9 in the container 5 by selecting a suitable float 7 and by adjusting the position of the float 7 on the sleeve 1.

Liquid is withdrawn from the container 5 via the tube 5 by suction and the flow rate of liquid withdrawn is monitored by any suitable sensor 21.

When the liquid level 9 is high as shown in Fig. 2 this raises the float 7 and the sleeve 1 away from the opening 4. Hence the flow of liquid is restricted only by the size of the opening 4 and the flow rate sensor 21 detects only a normal flow rate. As the liquid level falls, the float 7 and thus the lower part of the sleeve 1 fall to partially cover the opening 4.

Then, as shown in Fig. 3, the lower part of the sleeve 1 will obstruct sufficient area of the opening 4 to be drawn by suction towards the opening 4. The sleeve 1 will not slide down the tube any further and thus the -Feduced size of the opening 4 will remain constant while the suction continues. The flow rate sensor now detects a reduced flow rate signifying the contents of the container 5 is low.

When the sleeve 1 falls to its lower position, as shown in Fig. 4, the flowrate will be that permitted by the clearance between the sleeve 1 and the tube 2 at and above the liquid level 9. The sensor 21, senses a minimal flow rate and action can be taken to prevent air from being drawn into the tube 2 through the opening 4.

By adjusting the position of the float 7 on the sleeve 1, as represented in Fig. 5 the liquid level 9 at which the opening 4 is closed or partially closed may be adjusted. In the example shown in Fig. 5, closure takes place at a higher liquid level 9 than in Fig. 4.

A liquid sensing system composed of the flow rate sensor 21 in conjunction with the controller 20, as described can be used in apparatus for mixing chemicals described in U.K. application No. 8319296. In such an application the container 5 would contain a chemical concentrate and suction could be applied to the tube 2 by an oscillating bellows pump and the flow rate is then sensed by counting the number of oscillations of the pump, and hence a measure of the time, required to fill a chamber of known size.

The chamber, not shown in the drawings, can periodically be emptied by opening a solenoid operated valve and its state of fill is determined by conductivity level sensing probes. When the opening is partially sealed the number of pump oscillations to fill the chamber increases substantially and this provides a signal that the liquid level has fallen to near that of the valve seating.

In other embodiments of this invention the flow rate sensor 21 is of the type which gives a continuous output such as a turbine, Pelton wheel or venturi flowmeter.

Another embodiment a liquid level and flow rate controller 20 is shown in Figs. 6A, 6B, 7 and 8 and like reference numerals denote like parts to Figs. 1 to 5. As shown in Figs. 6A-8 a spherical float 1 2 is free to move vertically between the blanking plug 3 and the top of a guide 11 but is constrained laterally by the tube 2 and the guide 11. An opening 10 in the tube 2 is defined by a frusto-conical valve seating with grooves 1 3 on which the float 1 2 can engage.Referring to Fig. 7, the float 1 2 is here buoyed up by the liquid level 9 and liquid flows freely through the opening 1 0. As the the liquid level 9 falls, as shown in Fig. 8, the flow of liquid draws the float into the opening 1 0. The flow is then restricted to the volume of liquid that will pass through the clearance between the float 1 2 and the radial grooves 1 3 formed on the lower half of the valve seating. The upper half of the valve seating is smooth so that the surface tension will form a seal between the seating 10 and the smooth ball 12, preventing air being sucked into the hole 1 0.

Further embodiments of controller 20, not shown in the drawings, which can be adopted are a pivoted flap valve or a variant of the sleeve valve shown in Figs. 1, 2, 3, 4 and 5, in which the float and sleeve slide inside the tube 2. These variants are particularly suitable for narrow necked containers.

Claims (9)

1. A liquid level and fow rate sensing system comprising a tube or the like insertable within vessel and serving to draw liquid from the vessel via an opening in the tube, or valve adapted to partially seal the opening when the level of the liquid falls to a predetermined level to reduce the flow rate through the tube and a flow rate sensor for sensing when the flow rate is reducqd.

2. A system according to claim 1, wherein the valve takes the form of å sleeve attached to a float and moving along the tube.

3. A system according to claim 2, wherein the sleeve is arranged to completly seal the opening in the tube when the level of the liquid falls to near that of the float attached to the sleeve to prevent air being drawn into the tube.

4. A system according to claim 1, wherein the valve is a spherical float guided and constrained to move up and down at the side of a tube in the region of the opening in sealing relationship.

5. A system according to claim 4, wherein the opening has grooves to permit a minimal liquid displacement therethrough when the float seats thereon.

6. A system according to claim 1, wherein the valve is flap valve.

7. A system according to any one of the claims 1 to 6, wherein the sensor utilises a chamber of known volume whose time of filling is a measure of the flow rate.

8. A system according to any one of the claims 1 to 6, wherein the flow rate sensor is of the continuous type such as a turbine, Pelton wheel or venturi flowmeter.

9. A liquid level and flow rate sensing system or a liquid level and flow rate control ler substantially as described with reference to, and as illustrated in, any one or more of the Figures of the accompanying drawings.