GB2336210A - Sensing the presence of liquid of a predetermined specific gravity - Google Patents

Abstract

The apparatus comprises two liquid level detectors 16, 18 each comprising a float 30 and a pneumatic sensor 38 which responds to the rise and fall of it's corresponding float 30. The two floats are designed to respond to liquids of different specific gravities, e.g. one will float on water but not on petrol and the other will float on both water and petrol. The two sensors provide an indication, such as an audible or visible alarm, of firstly whether a liquid is present and secondly whether the liquid has a specific gravity above or below a predetermined value, e.g. they can indicate whether the liquid is water or a hydrocarbon. The apparatus is intended for use in sumps, such as those found in garage forecourts, to warn of the presence of a hazardous liquid before purging the sump. Sensing apparatus comprising a float mounted on a pivotal arm (see figure 4), and sensing apparatus comprising a float movable relative to a raft (see figures 6, 7 and 8) is also disclosed.

Description

2336210 SENSING SYSTEMS The present invention relates to sensing systems

for distinguishing between liquids having different specific gravities.

In garage forecourts and similar locations, there are located in the ground deep sumps housing pumps, valves and similar paraphernalia for controlling the movement of liquid hydrocarbons, such as petrol and diesel, between different tanks and locations. These sumps, over a period of time, accumulate ground-water entering as a result of seepage and sometime hydrocarbon liquids resulting from such effects as faulty valves and pipe fractures.

In order to maintain the equipment in the sump functioning properly, it is important to purge the sump periodically. However, while ground-water can be safely pumped out and discharged, problems arise when the sump contains liquid hydrocarbons when special equipment and precautions need to be taken.

Currently, to determine the contents of the sump, liquid needs to be extracted and analysed.

is It is an object of the invention to provide an improved sensing system.

According to the present invention there is provided a sensing system for sensing liquids in a container comprising first and second float devices to be located in the container, the first float device having a first float which responds only to a liquid having a specific gravity equal to or greater than a first predetermined specific gravity to move from a lower to a higher position, the second float cc having a float which responds only to liquid having a specific gravity equal to or greater than a second predetermined specific gravity to move from a lower to a higher position, the second predetermined specific gravity being lower than the first predetermined specific gravity, the first float device having a first pneumatic sensor providing an indication when the first float has risen and the second float device having second pneumatic sensor providing an indication when the second float has risen, said indications enabling a determination to be made as to whether there is liquid in said container and whether said liquid has a specific gravity equal to or greater than said first predetermined specific gravity or less.

Sensing systems for sensing the contents of sumps and embodying the present invention, will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 is a section through a sump containing the system; Figure 2 is a longitudinal section through one of the float devices of the system; Figure 3 is circuit diagram of the system; Figure 4 is a longitudinal section through a second embodiment of a sensing system; Figure 5 is a pneumatic circuit diagram for the system of Figure 4; and Figures 6 to 8 are side elevations of a further embodiment of the system respectively showing the relative positions when the sump contains water, a water/oil mixture and just oil respectively.

The sump shown in Figure 1 is a typical sump at a petrol station forecourt located below ground and containing pumps 4 and valve 6 (only one of each being shown).

An aperture 8 in the floor of the sump leads to a conduit 10 which extends to ground level and is connected to a discharge pump 12. Alternately, the pump may be located adjacent the aperture 8 or even lowered into the sump on a flexible hose if and when the sump is to be purged of liquids.

Mounted on the wall of the sump just above the base is the sensing system 14. The system 14 comprises a pair of float devices 16 and 18 located in side by side relationship. One of the float devices 16 is shown in more detail in Figure 2.

As shown, the device 16 has a cylindrical housing 20 containing a pair of axially spaced annular guides 22 and 24. The guides 22 and 24, which may be of brass, support a brass rod 26 for freely slidable axial movement.

The upper end of the rod 26 carries a radially outwardly extending upper flange 28 which, when it abuts the upper face of the guide 22, limits the downward movement of the rod 26. Just above the lower end of the rod 26, there is a radially outwardly extending lower flange 40 which limits the upward movement of the rod when it abuts the lower guide 40. The lower end of the rod carries a bulbous hollow float 30. Between the guides 22 and 24, the rod 26 carries a permanent magnet 32. Mounted on the outer wall of the cylinder 20 is an encapsulated reed relay 38 which has a pair of contacts which close when the rod is raised to bring the lower flange into abutment with the lower face of the lower guide 24 and at the same time bring the magnet 32 to a position immediately opposite the reed relay 38.

The float 30 is arranged to respond to a liquid having a specific gravity of 1.0 (eg water) or more entering the sump and will rise with the liquid. As the float rises it will cause the magnet 32 to rise and when the flange 40 abuts the guide 24, the magnet will trigger the reed relay 38 to close. The float 30 will not rise in response to liquids lighter than water eg petrol or diesel fuel.

The other float device 18 is of similar construction to the float device 16 but its float 30A is arranged to respond to liquids having a specific gravity of substantially below 1.0 eg a specific gravity of 0.50. Thus, the float 30A will rise in response to water as well as liquids having a specific gravity lower than water. Parts of the float device 18 similar to those of the float device 16 are similarly referenced but with the suffix A.

The floats 30 and 30A, when in the lower position, are arranged to lie below 2 to 5 cm above the base of the sump. Also, the relative positions of the reed relays and the magnets of the two float devices are so positioned that if both floats are rising at the same time in response to a liquid entering the sump. The float 30 will cause the reed relay 38 to operate before the float 30A causes its relay 38A to operate. Thus, for example, the float 30A may need to rise at least 2 em more than the float 30 before operating its corresponding reed relay 38A.

The circuit diagram is shown in Figure 3.

As can be seen, the reed relay contacts 38, connected in series with the parallel combination of a lamp 46 and the coil of a relay 44 across a battery 52. The reed relay contacts 38A are connected in series with the normally closed contact set 44A of the relay 44 and the parallel combination of a lamp 48 and alarm 50 across the battery 52.

In operation, with the sump empty and starting to fill up with water, the float 30 win rise and cause the contacts 38 to close. This will energise the lamp 46 to issue a warning that the sump contains water. At the same time, the relay 44 is energised and the contact set 44A is opened. When subsequently the float 30A rises to close the contacts 38A, the open contacts 44A will prevent the alarm 50 being energised.

If instead of water a liquid having a lower specific gravity enters the tank, the float 30 will not rise and so the contacts 39 remain open. The float 30A will, however, rise and cause the contacts 38A to close. Since the contact set 44A remains closed, the lamp 48 and the alarm 50 will be triggered to indicate that a hazardous condition exits.

It will be appreciated that while the two float devices use reed relays and magnets, other forms of sensors can be used for example photo electric, capacitive or pneumatic.

Where magnetically operated pneumatic sensors are used the control, alarm and pumping systems may also be pneumatic to avoid electrical activity in any area which may be exposed to combustible gases or other combustible materials.

The modified sensor system shown in Figure 4 comprises two sensor devices 60 and mounted one above the other in a tank or chamber which may collect a liquid.

The lower sensor device 60 comprises an arm 62 carrying a float 64 at a distal end thereof. The other end of the arm 62 supports a magnet 66. The arm is pivotally supported on a wall 58, by a pivot 68 at a point between the magnet 66 and float 64 which lies close to the magnet 66. A pair of stops 70,72 on opposite sides of the magnet 66 limit the angular movement of the arm 62 between a first position of rest in which the arm extends horizontally and a second position in which the arm is inclined to the horizontal with the float 64 lying above the pivot 68 (which position is achieved by the arm turning in an anticlockwise sense from the rest position).

A magnetically operated pneumatic switch 74 is mounted on the wall 58. The switch 74 incorporates a valve rigid with a magnetic member. The magnetic member can be displaced to open and close the valve in response to the presence or absence of a magnetic field. In this case, the magnetic field is supplied by the magnet 66. When the arm 62 is horizontal, the magnetic flux of the magnet 66 couples with the magnetic member to establish a first position of the valve. When the arm 62 is pivoted towards the stop 72, the magnetic member and the magnet become magnetically decoupled and the switch 74 is caused to adopt a second position.

When rising fluid encounters the float, it must not only overcome the weight of the float but also the strength of the magnetic coupling in order to cause the arm 62 to move about the pivot 68.

The point at which the pivot 68 is mounted on the wall 58 is horizontally adjustable (by means not shown) so that the magnet 66 can be moved closer to or further away from the sensor 58 and so vary the strength of magnetic coupling between the magnet 64 and the magnetic member. In a modification, the position of the magnet 66 may be moved along the arm 62 (by means not shown) to achieve the same effect.

The upper sensor device 80 is generally similar in construction to the device 60 having an arm 82 supporting a float 64 at one end and a magnetic 86 at the other end and supported on the wall 58 by a pivot 88. In this case, the two stops 90 and 92 are so positioned that, when at rest, the arm 82 slopes downwardly with respect to the horizontal so that the float 84 lies below the pivot 86. When the arm 82 is pivoted in an anticlockwise manner about the pivot 66, the stop 92 limits the displacement to a position in which the arm 82 extends horizontally.

A pneumatic switch 94 is mounted on the wall 58. The switch 94 has a magnetic valve member which is positioned to be magnetically coupled with the magnet 86 when the arm 82 is brought into the horizontal position against the stop 90 and decoupled from the magnet 86 when the arm 82 abuts the stop 90.

The two floats 84 and 64 are normally equally buoyant and capable of floating in any liquid which is likely to enter the tank or chamber, for example water and petroleum.

The magnetic coupling between the magnet 66 and the switch 74 (when the arm 62 is at rest) is set to a strength at which it will prevent the float 64 rising in response to petroleum but not water.

In operation, therefore, when the tank progressively fills with a liquid, if the liquid is petroleum the float 66 will not rise but the float 84 will.

The two switches 94 and 74 will be in the same state and this will indicate the presence of petroleum in the tank. If the tanks fills progressively with water, both floats 64 and 84 will rise and so the state of the two switches will have reversed. This then indicates the presence of water.

As will be appreciated, the horizontal position of the pivot pin 68 is movable to an optimum position to enable the system to differentiate between liquids of two specific gravities.

It will be appreciated that in such environments as the sumps in petrol stations, it is important to keep the sumps empty. If the sumps are full of water, they can be readily pumped out using a pneumatic pump 100. If the sumps contain petroleum, this represents a hazard and so pumping should be inhibited. The circuit in Figure 5 shows how the sensor systems of Figure 4 can be used in this situation. As can be seen, the valves 74 and 94 are feed from a pneumatic source 102 and their outputs are connected to respective inputs of a NOT gate 104 and an AND gate 106. When water is sensed, the NOT gate 104 supplies an output to a valve 110 which in turns connects the source 102 to the pump 100 and so drives the pump 100.

When petroleum is sensed, the AND gate 106 provides an output which activates an alarm 108. Thus, pumping is automatically effected when the liquid level in the sump reaches the upper float but is automatically inhibited at the same time, if the liquid is petroleum and not water.

While the two floats 64 and 84 have the same buoyancy, they may be arranged to have different buoyancies.

The use of pneumatic power to feed control signals to and from the sensor system has the advantage of low fire risk. It will, of course, be appreciated that hydraulic power can be used instead or even electrical power in non-flammable environments.

The modified system shown in Figures 6 and 7 comprise a floating raft 120 carrying a float 122 constrained for vertical movement relative to the raft 120 by an elongate cage 124. A pneumatic magnetically operable switch 128 is secured to the lower end of the cage 124. The float 122 carries a magnetic 126 which can magnetically coupled with the switch when the float 122 is in the lower position and decouple from the switch 128 when in a raised position. The switch is supplied by a pneumatic cable 130 which also acts to tether the raft 128 to the wall of the tank.

In operation, if the tank fills with water, the float 120 floats on the surface of the water and the float 122 will remain in its lower position. If instead of water or on top of the water, petroleum enters the tank, the raft, which is heavier than the petroleum, will sink below the petroleum. The float 122, which is lighter than the petroleum, will start to float on the petroleum and in turn rise relative to the raft 120 to the position shown in Figure 2. The state of the switch 128 will thus indicate when petroleum is present.

Of course, the specific gravities of the raft 120 and float 128 may be adjusted as required to enable the switch to distinguish between two liquids of different specific gravity.

The raft 120 may be supplied with a ground sensing pneumatic switch (not shown) which is activated when the raft 120 rests on the bottom of the tank and so indicates that the tank is empty.

Claims (14)

1. A sensing system for sensing liquids in a container comprising first and second float devices to be located in the container, the first float device having a first float which responds only to a liquid having a specific gravity equal to or greater than a first predetermined specific gravity to move from a lower to a higher position, the second float device having a float which responds to liquid having a specific gravity equal to or greater than a second predetermined specific gravity to move from a lower to a higher position, the second predetermined specific gravity being lower than the first predetermined specific gravity, the first float device having a first pneumatic sensor providing an indication when the first float has risen and the second float device having second pneumatic sensor providing an indication when the second float has risen, said indications enabling a determination to be made as to whether there is liquid in said container and whether said liquid has a specific gravity equal to or greater than said first predetermined specific gravity or less.

2. A system according to Claim 1, wherein said first predetermined specific gravity is 1 and said second predetermined specific gravity is 0.5.

3. A system according to Claim 1 or to Claim 2, wherein said first and second sensors comprise magnetically operable pneumatically sensors.

4. A system according to Claim 1 or to Claim 2, wherein said first and second sensors each comprise a reed relay and a magnet with the float causing relative movement between the two.

5. A system according to Claim 1 or to Claim 2, wherein each said float device comprises a cylindrical housing supporting a rod for axial movement, the rod carrying said float.

6. A system according to Claim 5, wherein said housing has a pair of longitudinally spaced guides for slideably supporting said rod and wherein said rod has a pair of spaced flanges which cooperate with said guides to limit the range of axial displacement of the rod.

7. A system according to any preceding claim, including a control circuit responsive to said sensors for providing a visual or audible alarm in response to said sensors providing an indication.

8. A system according to Claim 7, wherein said control circuit includes a first alarm which is activated by said second sensor when said second sensor provides an indication and disabled by said first sensor when said first sensor provides an indication.

9. A sensing system including a raft supporting a float, constraining means for constraining the float for movement relative to the raft in a direction having a vertical component relative to the raft, the float having a different specific gravity to the combined raft and constraining means, whereby when subjected to liquids having different specific gravities, both the float and raft will float in one liquid and only the float will float in the other liquid, and sensing means for sensing relative movement of the raft and float.

10. A system according to Claim 9, wherein the sensing means comprises magnetically operated pneumatic switch supported on said raft and a cooperating magnet incorporated in said float.

11. A sensing system comprising a pivotal arm supporting a float and a magnet, means for constraining the float for movement between two vertical positions, and a magnetically operated switch mounted adjacent the locus of the magnet when the float moves between its two positions, the magnet magnetically coupling the switch when the float is in its lower position, whereby when the float is subjected to a rising liquid, the liquid must not only be of greater specific gravity than the float, but also must overcome the magnetic coupling between the magnet and the switch in order to displace the float.

12. A system according to Claim 11, wherein the pivotal point of the arm is adjustable towards or away from the switch to increase or decrease the coupling between the two and thereby enable the float to be used to sense liquids of different specific gravity.

13. A system according to Claim 11 or to Claim 12, wherein the switch is a magnetically operated pneumatic switch.

14. A sensing system substantially as hereinbefore described, with reference to Figures 1 to 3, or Figures 4 and 5 or Figures 6 and 7 of the accompanying drawings.