WO2009106902A1

WO2009106902A1 - Liquid gauge apparatus and method

Info

Publication number: WO2009106902A1
Application number: PCT/GB2009/050208
Authority: WO
Inventors: Trevor John Poulter
Original assignee: Mechtronic Ltd
Current assignee: Mechtronic Ltd
Priority date: 2008-02-28
Filing date: 2009-02-28
Publication date: 2009-09-03
Anticipated expiration: 2010-08-28
Also published as: GB0803673D0

Abstract

Liquid gauge apparatus comprising: an immersion member having a passageway provided therein; and a gas pressure signal device arranged to measure a pressure of gas in said passageway, the pressure signal device being configured to provide an output corresponding to a difference between a pressure of gas in the passageway and a reference pressure, wherein the immersion member is configured to be supported with at least a portion of the immersion member within a liquid containment volume of a liquid storage tank, said portion of the immersion member having an aperture therein whereby the passageway is provided in fluid communication with the storage tank, the apparatus being further configured such that an increase in a depth of immersion of the aperture in a liquid contained in the tank causes an increase in a gas pressure in the passageway, the apparatus further comprising means for forcing a gas into the passageway whereby liquid contained in the passageway substantially above the level of said aperture may be forced out from the immersion member through the aperture.

Description

LIQUID GAUGE APPARATUS AND METHOD

FIELD OF THE INVENTION

The present invention relates to liquid gauge apparatus and a method of gauging an amount of liquid. In particular, but not exclusively, the invention relates to apparatus for gauging a level of liquid in a liquid storage tank. More particularly, but not exclusively, the invention relates to apparatus and a method for gauging a level of liquid in a storage tank of a road tanker. Most particularly, but not exclusively, the invention relates to apparatus and a method for gauging a level of hydrocarbon based fuels and similarly flammable materials in a storage tank of a road tanker.

BACKGROUND

Conventional methods of determining a level of liquid in a storage tank include the use of a simple dipstick, which is dipped into a tank until an end of the dipstick contacts the bottom of the tank. When the dipstick is withdrawn, a determination of the length of the dipstick that has been wetted by liquid in the tank provides an indication of the liquid level in the tank, and hence of the quantity of liquid remaining in the tank.

The problem exists that, in the case of a road tanker, a person using the dipstick must climb on top of the tanker in order to dip the dipstick into the tank. Such activities are potentially dangerous, particularly in adverse weather conditions such as wind, rain or icy conditions.

An alternative method is the use of a sight, e.g. a glass or plastic tube, that is mounted outside the tank. The sight is connected to the tank at a lower region of the tank and is mounted in a generally upright orientation along an outer wall of the tank. The disadvantage of such devices is that, since the level of liquid in the sight corresponds to the level of liquid in the tank, it can be difficult for an operative to determine the level of the liquid from ground level. The problem is particularly acute in the case of transparent liquids such as petroleum.

One method of measuring liquid levels involves the use of one or more electrical sensors. However, particular care must be exercised if electrical sensors are to be used in proximity with flammable materials due to the risk of explosion. It is therefore desirable to provide liquid gauge apparatus that may be used by an operative standing on the ground next to the tanker, and which may safely be used in the vicinity of flammable or explosive liquids and gases.

SUMMARY OF THE INVENTION

In a first aspect of the invention there is provided liquid gauge apparatus comprising: an immersion member having a passageway provided therein; and a gas pressure signal device arranged to measure a pressure of gas in said passageway, the pressure signal device being configured to provide an output corresponding to a difference between a pressure of gas in the passageway and a reference pressure, wherein the immersion member is configured to be supported with at least a portion of the immersion member within a liquid containment volume of a liquid storage tank, said portion of the immersion member having an aperture therein whereby the passageway is provided in fluid communication with the storage tank, the apparatus being further configured such that an increase in a depth of immersion of the aperture in a liquid contained in the tank causes an increase in a gas pressure in the passageway, the apparatus further comprising means for forcing a gas into the passageway whereby liquid contained in the passageway substantially above the level of said aperture may be forced out from the immersion member through the aperture.

The apparatus has the advantage that a risk that a false reading of pressure will be provided by the liquid gauge apparatus due to the presence of liquid in the immersion member can be substantially eliminated. This is because liquid that might cause the false reading may be expelled from the immersion member through the aperture by forcing gas through the passageway of the immersion member.

By liquid containment volume is meant a region of the tank in which it is desirable to gauge the level of liquid in the tank.

Preferably the apparatus comprises display means coupled to the pressure signal device, the display means being configured to provide a display of a quantity of a liquid remaining in the storage tank based on the output of the pressure signal device. Some embodiments of the invention have the advantage that the level of liquid in the storage tank may be determined by inspection of a display that may be positioned at a height within the comfortable viewing range of an operative on the ground adjacent the storage tank. In some embodiments the gauge is positioned on a side of a road tanker having a liquid storage tank, where it may be inspected by a tanker operative standing on ground.

For the present purposes reference to 'gas' is understood to refer to a gaseous fluid medium and not to gasoline.

The reference pressure may correspond to ambient atmospheric pressure. Thus, the reference pressure will vary as atmospheric pressure varies.

Variations in liquid level determination due to fluctuations in atmospheric pressure can introduce significant errors into the determination of the quantity of liquid. This is because liquid storage tanks used by road tankers are generally elongate in a horizontal direction. Consequently, liquid stored in the tanker has a relatively large exposed surface area. Small variations in the depth of the liquid can therefore correspond to a significant volume of liquid.

Preferably a pressure of gas above liquid in the liquid storage tank, not being gas in the immersion member, is maintained at the same pressure as atmospheric pressure by means of a vent member whereby an inside of the tank may be provided in fluid communication with ambient atmosphere.

Preferably the immersion member comprises a tube member.

Preferably the immersion member has a free end arranged to be supported in said liquid storage volume of the storage tank.

The aperture may be provided in a sidewall of the immersion member.

The aperture may be provided at said free end of the immersion member.

A plurality of apertures may be provided in the immersion member. Preferably the immersion member is a substantially elongate member provided in a substantially upright orientation, the pressure signal device being arranged to measure a pressure of gas at a position of the immersion member above said aperture.

The apparatus may be operable upon a command by a user to force gas into the immersion member for a predetermined period of time, preferably between 1 and 30 seconds, more preferably between around 1 and around 2 seconds.

Alternatively or in addition the apparatus may be operable to force gas through the immersion member substantially continuously. The apparatus may be arranged to force the gas through the immersion member at a prescribed flow rate.

The apparatus may be arranged to measure the pressure of gas in the immersion member whilst gas is being forced through the immersion member.

Alternatively or in addition the apparatus may be arranged to measure the pressure of gas in the immersion member whilst gas is not being forced through the immersion member.

The apparatus may be arranged to measure a pressure of gas in the immersion member whilst gas is substantially under a static flow condition, i.e. conditions of substantially zero flow through the immersion member.

In some embodiments the immersion member comprises a tube member having an outer diameter of around 4mm and an inner diameter of around 2mm, the tube member having a length of around 2m. It is to be appreciated that the internal volume of the tube member of this embodiment is relatively small such that any liquid contained in the tube member can be expelled by pumping a gas under pressure through the tube member in a relatively short amount of time, of the order of 1 to 2 seconds.

Preferably said gas is drawn from said storage tank.

The gas may be a non-flammable gas.

The gas may be provided under pressure from a gas storage volume. In a second aspect of the invention there is provided liquid gauge apparatus comprising: an immersion member comprising a hose member having a passageway provided therethrough, the immersion member having an entrance aperture at a first position of the passageway, the entrance aperture being provided in fluid communication with a gas supply, and an exhaust aperture at a second position of the passageway axially displaced from the first position, a gas pressure signal device having a gas pressure sensor arranged to measure a pressure of gas at said entrance aperture, the pressure signal device being configured to provide an output corresponding to a difference between a gas pressure at the entrance aperture and a reference pressure, wherein the immersion member is configured to be supported with at least a portion of the immersion member within a liquid containment volume of a liquid storage tank, the apparatus being further configured to force a gas from said gas supply through the passageway from the entrance aperture to the exhaust aperture, the hose member being configured such that a dimension of the portion of the passageway provided by the hose member may be enlarged from a first value to a second value against a pressure of liquid in the liquid storage tank in which the immersion member is immersed by forcing gas from the gas supply through the entrance aperture.

Preferably a gas flow restrictor is provided between the gas supply and the gas pressure sensor of the pressure signal device.

Preferably the immersion member comprises a lay-flat hose member.

In the case where the immersion member comprises a lay-flat hose member, the first value of the dimension of the passageway may correspond to a value of substantially zero, i.e. to a substantially closed fluid passage.

For the present purposes, a lay-flat hose member is defined as a hose member that adopts a relatively flat condition in the absence of fluid pressure within the hose. The lay-flat hose member is considered to have a 'passageway' suitable for passage of fluid even when the hose is in a substantially flattened condition whereby fluid cannot be passed along the hose without deformation of the hose from the flattened condition.

As an amount of liquid in the tank above the level at which the lay-flat hose is provided increases, the pressure on walls of the hose increases. Thus a greater gas pressure at the entrance aperture of the immersion member is required in order to force gas along the immersion member from the entrance aperture to the exhaust aperture.

Preferably the immersion member comprises a polymeric material, such as polythene.

The immersion member may be arranged so that the entrance aperture is located below the exhaust aperture.

Alternatively the immersion member may be arranged so that the entrance aperture is located above the exhaust aperture.

Preferably the apparatus is arranged whereby at least a first portion of the immersion member is provided above a second portion of the immersion member, the first portion being axially spaced apart from the second portion.

The first portion may be substantially vertically above the second portion.

At least a portion of the immersion member may be provided in the liquid containment volume in a substantially horizontal plane.

The apparatus may be configured to discharge gas emerging from the exhaust aperture inside the liquid storage tank.

The apparatus may be configured to discharge the gas inside the liquid storage tank above an upper limit of the level of liquid in the storage tank.

Alternatively or in addition the apparatus may be configured to discharge gas emerging from the exhaust aperture outside the liquid storage tank.

This feature has the advantage that a risk that gas from the gas supply mixes with liquid in the liquid storage tank, or vapours generated by evaporation of liquid in the liquid storage tank, may be substantially reduced. For example, if the liquid is petroleum, and the gas is air, a highly explosive air/petroleum mix may be created if the air is discharged into the liquid storage tank. This feature has the advantage that in situations where it is desirable to use air as the gas, mixing of air with a liquid in the tank (such as liquid petroleum) may be avoided. For example, atmospheric gas may be compressed using a compressor, and then fed into the immersion member.

Preferably the gas comprises at least one selected from amongst a non-flammable gas, nitrogen, argon and air. In particular, it is generally preferred that the gas is substantially chemically inert with respect to the liquid in the tank.

Preferably the apparatus comprises a controller configured to receive and to store: a pressure data value corresponding to a pressure level input signal from said gas pressure signal device; and a quantity data value corresponding to an input by a user of a quantity of liquid contained in the liquid storage tank.

The apparatus may be configured to calculate a density value corresponding to the density of liquid contained in the liquid storage tank based on said pressure level input signal and said quantity value.

Preferably the apparatus is further configured to receive an input from a user of a liquid type corresponding to the type of liquid that has been added to the storage tank.

The apparatus may be configured to compare the density value with a density reference value corresponding to the liquid type input by the user, the apparatus being further configured to determine whether the density value corresponds to the density reference value.

This feature has the advantage that the apparatus can provide an alert in the event of a mismatch between data entered into the apparatus by a user, and measurements made by the apparatus.

The apparatus may be configured to request a user to re-enter at least one selected from amongst said quantity value and said liquid type if said density value does not correspond to the density reference value.

This feature has the advantage that a user is assisted in identifying the data that has been entered wrongly into the apparatus. Preferably if the density value does not correspond to the density reference value the apparatus is configured to determine a proposed liquid type being a type of liquid having a density corresponding to the density value and to request a user to input a confirmation whether or not the liquid added by the user corresponds to the proposed liquid type.

Alternatively the apparatus may be configured to determine whether the pressure data value and the quantity data value are consistent with one another based on the input by the user of the liquid type.

The apparatus may be configured to request a user to re-input at least one selected from amongst said quantity value and said liquid type if said particular values of pressure data value and quantity data value are not consistent with the input by the user of the liquid type.

If said particular values of pressure data value and quantity data value are not consistent with the input by the user of the liquid type the apparatus may be configured to determine a proposed liquid type being a type of liquid for which the pressure data value and quantity data value are consistent and to request a user to input a confirmation whether or not the liquid added by the user corresponds to the proposed liquid type.

The controller may be provided with a lookup table comprising a plurality of respective different quantity data values and corresponding pressure data values for each of a plurality of liquids that are to be stored in the storage tank.

This feature has the advantage that an accurate assessment of the quantity of liquid remaining in the tank can be made based on the output of the pressure signal device.

The liquid storage tank may be provided with a pressure release valve arranged to prevent a pressure in the tank exceeding a critical value.

The liquid may be a liquid fuel.

In a third aspect of the invention there is provided a liquid storage tank comprising apparatus according to the first or second aspects of the invention. In a fourth aspect of the invention there is provided a road vehicle having a liquid storage tank according to the third aspect of the invention.

The vehicle may be a road tanker.

In a fifth aspect of the invention there is provided a tanker for transporting hydrocarbon based liquid comprising apparatus according to the first or second aspects of the invention.

In a sixth aspect of the invention there is provided a method of measuring a level of liquid comprising: providing liquid gauge apparatus comprising: an immersion member having a passageway provided therein; and a gas pressure signal device having a gas pressure sensor in fluid communication with said passageway, the pressure signal device being configured to provide an output corresponding to a difference between a gas pressure at the sensor and a reference pressure; wherein the immersion member is configured to be supported with at least a portion of the immersion member within a liquid containment volume of a liquid storage tank, said portion of the immersion member having an aperture therein whereby the passageway is provided in fluid communication with the storage tank, the apparatus being further configured such that an increase in a depth of immersion of the immersion member in a liquid contained in the tank causes an increase in a gas pressure in the immersion member, the apparatus comprising means for forcing a gaseous fluid into the passageway of said immersion member whereby liquid contained in the passageway substantially above the level of said aperture may be forced out from the immersion member through the aperture; immersing at least a portion of the immersion member in a liquid; and measuring a pressure of gas in the immersion member.

In a seventh aspect of the invention there is provided a method of measuring a level of liquid comprising: providing liquid gauge apparatus comprising: an immersion member comprising a hose member having a passageway provided therethrough, the immersion member having an entrance aperture at a first position of the passageway, the entrance aperture being provided in fluid communication with a gas supply, and an exhaust aperture at a second position of the passageway axially distal the first position, a gas pressure signal device having a gas pressure sensor arranged to measure a pressure of gas at said entrance aperture, the pressure signal device being configured to provide an output corresponding to a difference between a gas pressure at the entrance aperture and a reference pressure, wherein the immersion member is configured to be supported with at least a portion of the immersion member within a liquid containment volume of a liquid storage tank, the apparatus being further configured to force a gas from said gas supply through the passageway from the entrance aperture to the exhaust aperture, the hose member being configured such that a dimension of the portion of the passageway provided by the hose member may be enlarged from a first value to a second value against a pressure of liquid in the liquid storage tank in which the immersion member is immersed by forcing gas from the gas supply through the entrance aperture; immersing at least a portion of the immersion member in a liquid; and measuring a pressure of gas in the immersion member.

The method according the sixth or seventh aspects may further comprise the step of providing the liquid gauge apparatus in a liquid storage tank.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 shows liquid gauge apparatus according to an embodiment of the invention;

FIGURE 2 shows liquid gauge apparatus according to a further embodiment of the invention; and

FIGURE 3 shows liquid gauge apparatus according to a variation of the embodiment of FIG. 2.

DETAILED DESCRIPTION

In an embodiment of the invention, liquid gauge apparatus 100 is provided as shown generally in FIG. 1. The apparatus 100 has an immersion member 120 in the form of a rigid hollow tube, connected at a first end 121 to a pressure transducer 1 10. The pressure transducer 1 10 is configured to measure a pressure of gas contained within an inner volume 125 of the immersion member 120. Internal walls of the immersion member 120 define the inner volume 125.

It is to be understood that throughout the specification the word 'gas' is used to refer to a gaseous fluid and not to liquid gasoline.

A second end 122 of the immersion member 120 opposite the first end is open to allow liquid to pass from a liquid storage tank 150 in which the immersion member 120 is placed, and into the inner volume 125.

The immersion member 120 is mounted to the liquid storage tank 150 such that the second end 122 of the immersion member 120 is contained within a liquid containment volume of the liquid storage tank 150.

The pressure transducer 1 10 is coupled to a controller 140 having a user-interpretable display unit 142. The display unit 142 is configured to provide a display of a liquid level in the liquid storage tank 150. The controller 140 includes processing means to receive a signal from the transducer 1 10 and provide a corresponding output via the display unit 142.

In the embodiment of FIG. 1 the display is of an LED ladder type having a series of LED elements. The display unit 142 is configured to illuminate an increasing number of LED elements as the pressure detected by the pressure transducer 1 10 increases thereby to provide an indication of the quantity of liquid stored in the storage tank 150.

A gas pump 160 is provided, the pump 160 being arranged to pump gas from an upper region of the storage tank 150 into the immersion member 120. The purpose of the pump 160 is to force any liquid contained within the immersion member 120 out from the immersion member 120. When the pump 160 is turned off, liquid is substantially prevented from re-entering the immersion member 120 via the opening 122 due to the pressure of gas in the immersion member 120.

Other arrangements are also useful. For example, the pump 160 may be arranged to pump gas from an outside of the storage tank 150 or from a gas supply tank or other supply into the immersion member 120. As a consequence of the presence of pump 160, a measurement of head of pressure by pressure transducer 1 10 provides a more accurate indication of a quantity of liquid in the storage tank 150 compared with a system without such a pump 160.

It is to be appreciated that if further liquid is subsequently added to the storage tank after purging the liquid from immersion member 120 by means of gas, a resulting increasing in head of pressure may cause some liquid to enter the immersion member 120.

The embodiment of FIG. 1 has the advantage that excess liquid that becomes trapped in the immersion member 120 may be removed and the system returned to a condition in which a correct reading of a level of liquid in the storage tank 150 may be obtained.

Excess liquid may become trapped in the immersion member 120 for example in the circumstances in which liquid is pumped into the storage tank 150 at a first temperature during a relatively warm period of a day, and the liquid subsequently cooled to a second temperature lower than the first temperature overnight. The temperature of gas trapped in the immersion member 120 will decrease and consequently the gas will contract. This may have the effect that further liquid is drawn into the immersion member 120. Consequently, the head of pressure measured by the pressure sensor 1 10 may not correspond correctly to the amount of liquid in the storage tank 150.

In the embodiment of FIG. 1 , prior to performing a measurement of a pressure of gas in the immersion member 120 the apparatus 100 is configured to pump a prescribed amount of gas through the immersion member 120 in order to expel any liquid contained in the immersion member 120.

Other arrangements are also useful. For example, in some embodiments the apparatus is arranged to provide a flow of gas substantially constantly through the immersion member 120.

A flow of gas through the immersion member 120 may be provided at a substantially constant flow rate.

In some embodiments a pressure of gas in the immersion member 120 is measured whilst gas is flowing through the immersion member 120. In some embodiments a pressure of gas is measured whilst gas is in a substantially static no-flow condition in the immersion member 120.

The presence of the gas pump 160 has the further advantage that liquid present in the immersion member 120 due to turbulence or 'sloshing' during pumping of liquid into the storage tank 150 can be removed.

One manner of operation of apparatus 100 of the embodiment of FIG. 1 is described below.

Prior to delivering liquid from a storage tank 150, gas pump 160 is activated and gas is drawn from an upper region of the storage tank 150 through the pump 160 and into the immersion member 120. The pump 160 is activated for a period sufficient to expel liquid from the immersion member 120 such that the immersion member 120 is substantially free of liquid. In some embodiments the pump 160 is activated for a period of from around 1 second to around 5 seconds before being deactivated.

When the gas pump 160 is deactivated, the gas pressure in the immersion member 120 is measured once the pressure has stabilised.

Road tanker liquid storage tanks are generally filled at a depot by an operative. In some cases, the operative empties the storage tank before refilling with fresh liquid. In some cases, the operative fills a storage tank that already contains a significant quantity of liquid with further liquid (of the same or similar type).

Some embodiments of the invention are configured to allow an operative to input to the apparatus 100 (e.g. via controller 140) an indication of the amount of liquid that has been added to the storage tank 150. In some embodiments the apparatus 100 is also configured to request a user to further input an indication of the type of liquid that has been added to the tank (e.g. 'Diesel Oil', 'Fuel Oil', 'Paraffin', 'Spirit' etc).

In some embodiments, liquid gauge apparatus 100 is configured to calculate a density of the liquid that has been added, based on the indication of the amount of liquid that has been added by the user and the pressure of gas in the immersion member 120 as measured by the pressure sensor 1 10. In some embodiments in which a user also inputs an indication of the type of liquid that has been added, the apparatus 100 is configured to calculate a density value of the liquid as described above. If the density value calculated by the apparatus 100 is within an expected range of density values of the particular liquid indicated by the user, the apparatus 100 is configured to accept that the liquid that has been added is the liquid that the user/operator has indicated has been added.

However, if the density value calculated by the apparatus 100 is not within the expected range of density values, the apparatus 100 is configured to determine the most likely type of liquid that has been added based on the calculated density value. The apparatus 100 is configured to provide to the user an indication of the type of liquid that the apparatus 100 considers has been added.

In some embodiments of the invention, in the event that the density of the liquid input to the storage tank 150 as calculated by the apparatus 100 is not consistent with the density of the liquid that the operator has indicated has been added, the apparatus 100 is configured to request the user to re-enter the indication of the quantity of liquid added, and/or the type of liquid that has been added.

In order to determine the density of liquid that has been added based on the pressure reading, in some embodiments of the invention the apparatus 100 is provided with data corresponding to a strapping table (or 'look up' table), comprising expected pressure values for prescribed quantities of a given liquid. Thus, in some embodiments the table is provided with pressure values corresponding to quantities of a given liquid of from (say) 100 litres to 4000 litres in 10 litre increments (i.e. 100, 1 10, 120, ... 4000).

If a user inputs to the apparatus 100 that 4000 litres of gas oil have been added to the storage tank, the apparatus 100 is configured to determine from the strapping table that a pressure reading of (say) 200mbar (2OkPa) above atmospheric pressure is expected to be output by the pressure sensor 1 10 if 4000 litres of gas oil have in fact been added. Gas oil typically has a relative density (compared with water) in the range 0.81 to 0.87.

If however a pressure reading of (say) 165mbar (16.5kPa) is output by the pressure sensor 1 10, the apparatus 100 is configured to determine that in fact a different liquid may have been added. In some embodiments, if the apparatus 100 determines that the density of liquid in fact falls within the range corresponding to a different liquid, the apparatus 100 is configured to output an indication of the type of liquid that the apparatus 100 considers has been added.

In some cases, two or more liquids have identical or similar values of relative density such that it is difficult or impossible to distinguish between the two based on density values. Thus, in some embodiments of the invention, in the event that the apparatus

100 determines that the actual density of the liquid added to a tank 150 does not correspond to that of the liquid the user has indicated has been added, and the density of the liquid the apparatus 100 determines has been added corresponds to more than one liquid from a list of two or more liquids, the apparatus 100 is configured to request a user to confirm the type of liquid that has been added to the storage tank 150 from a list of the two or more liquids.

Some embodiments of the invention such as that of FIG. 2 have the advantage that the apparatus 100 'self calibrates' every time a new load of liquid is added to the storage tank 150, since the user inputs to the apparatus 100 the amount of liquid present in the tank 150 following loading of the tank 150 with the liquid.

This is in contrast to prior art gauge apparatus in which the apparatus is pre-calibrated. Any discrepancy between a gauge of a known system used to fill a storage tank and known gauging apparatus of the storage tank 150 can lead to problems.

For example a liquid fuel gantry system for filling one or more storage tanks 150 of a road tanker may indicate that 4,000 litres of liquid has been dispensed into a tanker's storage tank 150. However the tanker's own prior art gauging system may indicate that only 3,900 litres have been delivered. A discrepancy of 100 litres therefore exists.

If the liquid is delivered to a customer by a seller by means of the road tanker, and the contents of the storage tank 150 delivered, the tanker's gauging system will indicate that only 3,900 litres have been delivered to the customer. Revenue in respect of 100 litres of fuel will therefore be lost by the seller since the seller originally paid monies in respect of 4000 litres of liquid.

In the case of some embodiments of the present invention, liquid gauge apparatus 100 is configured to accept that the pressure reading of pressure gauge 1 10 corresponds to the quantity of liquid that the user inputs to the apparatus 100 by means of the controller 140 as having been added. The apparatus 100 therefore calculates the quantity of liquid remaining in the tank at any given time based on a consideration that the pressure measured by pressure sensor 1 10 at the time following the filling operation corresponds to the presence of 4,000 litres of liquid in the case of the above example, being the amount of liquid indicated on the gantry system used to deliver liquid to the tank 150 in that example.

Some embodiments of the invention have the advantage that the apparatus 100 can compensate for fluctuations in volume of a liquid due to variations in temperature and/or pressure.

Thus, if a tank 150 of a road tanker is filled with hot liquid fresh from a fuel refinery, apparatus 100 according to some embodiments of the invention is configured to flush (or 'purge') liquid from the immersion member 120 by means of a flow of gas through the immersion member 120 when it is required to measure a quantity of liquid in the tank 150. This is in order to allow a more accurate measurement to be made of the amount of liquid present in the storage tank 150 before (say) delivery of the liquid commences.

This is because cooling of gas trapped in the immersion member 120 may result in liquid being drawn into the immersion member 120. Consequently, liquid gauge apparatus 100 may indicate that an amount of liquid in the tank 150 following cooling of the liquid is less than the amount of hot liquid originally dispensed into the tank 150.

It is to be understood that some embodiments of the invention are not configured to meter liquid output from the storage tank 150. Rather, some embodiments are configured to gauge the amount of liquid input to the storage tank 150, and to provide an indication of the quantity of liquid remaining in the storage tank 150 at a given moment in time based on a measurement by pressure sensor 1 10 of the pressure of gas trapped in the immersion member 120.

In some embodiments, an indication is provided of the type of liquid in the liquid storage tank 150. In some embodiments the indication is provided by means of a colour provided on a display panel, or any other suitable indication. In some embodiments, when a liquid storage tank 150 is empty, an indication is provided that the tank is empty, together with an indication of the type of liquid that was most recently present in the tank.

In a further embodiment of the invention, liquid gauge apparatus 200 is provided as shown generally in FIG. 2.

The apparatus 200 of FIG. 2 has an immersion member 220 having a length of hose of the 'lay-flat' type. The lay-flat hose has a relatively low resistance to deformation in a radial direction. The hose is positioned such that a first (lower) end 221 is located close to a lowest region of the liquid storage tank 250. In the embodiment of FIG. 2, the immersion member 220 is made of polythene or other readily deformable material resistant to attack by liquid to be stored in the storage tank 250.

The first end 221 of the immersion member 220 is connected to a feed tube 215 that is in turn connected to a gas supply 260. In the second embodiment, the gas supply is a pressurised air supply. In alternative embodiments the gas supply 260 is arranged to supply another gas instead of air. For example, the gas supply 260 may be arranged to supply pressurised nitrogen, argon, or any other kind of gas which may safely be used in any given application. In some embodiments the gas is drawn from the liquid storage tank 250.

A flow restrictor 270 is provided at a location of the feed tube 215 between the gas supply 260 and the first end 221 of the immersion member 220 (see below).

In the embodiment of FIG. 2 a pressure gauge 208 is coupled to the feed tube 215 to provide an indication of a pressure of gas in the feed tube 215. The pressure gauge 208 is arranged to measure pressure in the feed tube 215 at a location between the flow restrictor 270 and the first end 221 of the immersion member 220.

A second end 222 of the immersion member 220 opposite the first end protrudes above an upper limit of a liquid level in the tank 250.

In some alternative embodiments the second end 222 is below the upper limit of the liquid level of the tank 250. In the embodiment of FIG. 2 the second end 222 of the immersion member is desirably positioned to protrude out from and above the tank 250.

In some embodiments the second end 222 is connected to an exhaust member 280 in the form of an exhaust pipe that is vented to atmosphere at a suitable location. The tank 250 is itself vented to atmosphere via a vent arrangement shown schematically at 295.

In use, gas is supplied to the feed tube 215 from the gas supply 260. The gas passes along the feed tube 215, through the flow restrictor 270, to the lay-flat hose 220.

The gas is then forced along the length of the immersion member 220 before being vented to atmosphere through the exhaust member 280. The immersion member 220 and/or exhaust member 280 may or may not be of a length sufficient to protrude above an upper limit of the level of liquid of the tank 250.

In the absence of liquid in the tank 250, the pressure on walls of the lay-flat hose 220 within the tank 250 is the same as ambient atmospheric pressure assuming the gas pressure in the tank 250 is atmospheric. However, when liquid is introduced into the tank 250, an increase in pressure on walls of the immersion member 220 occurs. Consequently, a pressure of gas in the feed tube 215 that is required in order to force gas through the lay-flat hose 220 and out from the exhaust member 280 is increased relative to that required when the tank 250 is empty of liquid.

The flow restrictor 270 is arranged such that the pressure of gas upstream from the flow restrictor 270 is greater than the pressure of gas downstream from the flow restrictor

270. It is to be understood that in designing apparatus according to some embodiments of the invention the pressure of gas supplied by the gas supply 260 must be greater than or equal to the pressure required to force gas through the immersion member 220 when the tank 250 is filled to a maximum level.

In some embodiments an electronic pressure regulator is provided to control a pressure of gas supplied by the gas supply 260.

The embodiment of FIG. 3 is similar to that of FIG. 2 and similar features are labelled with the same reference numerals. In the embodiment of FIG. 3 an electrical pressure transducer 210 is coupled to the feed tube 215. The transducer 210 is also coupled to an electronic controller 240 having a display 242. The transducer 210 is arranged to measure pressure in the feed tube 215 at a location between the flow restrictor 270 and the first end 221 of the immersion member 220.

In the embodiment of FIG. 3 the display 242 has an LED ladder element arranged to provide a display of a level of liquid in the storage tank 250. An increasing number of LEDs of the element are illuminated as the pressure in the feed tube 215 increases, indicating an increase in liquid level in the tank 250.

The apparatus 200 is typically installed into a tank 250 when the tank 250 is empty. Once installed, with no liquid in the tank 250 and a pressure in the tank 250 of a prescribed value (such as that of ambient atmosphere), the apparatus 200 is calibrated such that a reading of the display 242 corresponds to an empty tank 250. This is performed by forcing gas through the flow restrictor and through the immersion member 220 and measuring an output of the pressure transducer 210 thereby obtaining a measure of the pressure of gas in the feed tube 215.

When liquid is introduced into the tank 250, a level of liquid in the tank 250 increases and in the embodiment of FIG. 3 the first end 221 of the immersion member 220 becomes immersed in liquid. As the level of liquid in the tank 250 continues to rise, a head of pressure exerted by the liquid on a wall of the immersion member 220 increases. The pressure of gas in the feed tube 215 therefore increases and the controller 240 registers this increase.

It will be appreciated that apparatus 200 according to some embodiments of the invention may be used with a wide variety of liquids including liquid gases. For example, apparatus according to some embodiments of the invention may be used with water, beverage liquids, dairy liquids such as milk, oils, petroleum, liquid petroleum gas (LPG) etc.

It is to be understood that apparatus 200 according to FIG. 2 and FIG. 3 may be provided with a similar controller 240 to the controller 140 described above in respect of the embodiment of FIG. 1.

In some embodiments apparatus 200 as shown in FIG. 2 and FIG. 3 is provided with a controller 240 arranged to request an operative to input an amount of liquid that is present in the storage tank 250, and the type of liquid that is present. For example, this information may be requested by the controller 240 following a filling operation. In some embodiments an operative responsible for filling the tank 250 with liquid configures the controller 240 to receive this information.

In some embodiments including some embodiments similar to that shown in FIG. 1 , the controller is configured to determine whether the pressure of gas measured by pressure transducer 210 corresponds to that expected based on the type of liquid input by the operative to the controller 240 as being present in the tank 250 and the amount of liquid indicated by the operative as being present in the tank 250 without calculating a density of the liquid. In some embodiments, the apparatus 200 is configured to refer to a strapping table or 'look up' table to determine the pressure of gas expected under these circumstances.

As discussed in respect of the embodiment of FIG. 1 , in some embodiments the apparatus 100, 200 is configured to calculate a density of the liquid in the tank based on the amount of liquid in the tank and the pressure measured by the transducer 1 10, 210 in the feed tube 1 15, 215.

If some embodiments, if the pressure of gas measured by transducer 1 10, 210 does not correspond to that expected, the apparatus 100, 200 may be configured to query the operative, requesting confirmation of liquid type and quantity added.

It is to be understood that reference herein to addition or adding of liquid to a tank 150, 250 includes addition or adding of liquid to a tank 150, 250 that is initially empty of liquid, as well as to a tank 150, 250 that already contains some liquid.

In some embodiments, when an operative has topped up a tank 150, 250 that already contains liquid, and the operator is requested to input an amount of the liquid in the tank 150, 250, the operative is required to input a value of the total amount of liquid contained in the tank 150, 250, and not just the amount that has been added. In some embodiments the apparatus 100, 200 is configured to allow the operator to input an amount of liquid added, the apparatus 100, 200 adding this amount to the amount determined to be present in the tank 150, 250 by the controller 140, 240 before the further liquid was added. Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

CLAIMS:

1. Liquid gauge apparatus comprising: an immersion member having a passageway provided therein; and a gas pressure signal device arranged to measure a pressure of gas in said passageway, the pressure signal device being configured to provide an output corresponding to a difference between a pressure of gas in the passageway and a reference pressure, wherein the immersion member is configured to be supported with at least a portion of the immersion member within a liquid containment volume of a liquid storage tank, said portion of the immersion member having an aperture therein whereby the passageway is provided in fluid communication with the storage tank, the apparatus being further configured such that an increase in a depth of immersion of the aperture in a liquid contained in the tank causes an increase in a gas pressure in the passageway, the apparatus further comprising means for forcing a gas into the passageway whereby liquid contained in the passageway substantially above the level of said aperture may be forced out from the immersion member through the aperture.

2. Apparatus as claimed in claim 1 comprising display means coupled to the pressure signal device, the display means being configured to provide a display of a quantity of a liquid remaining in the storage tank based on the output of the pressure signal device.

3. Apparatus as claimed in claim 1 or claim 2 wherein the reference pressure corresponds to ambient atmospheric pressure.

4. Apparatus as claimed in any preceding claim wherein a pressure of gas above liquid in the liquid storage tank, not being gas in the immersion member, is maintained at the same pressure as atmospheric pressure by means of a vent member, whereby an inside of the tank may be provided in fluid communication with ambient atmosphere.

5. Apparatus as claimed in any preceding claim wherein the immersion member comprises a tube member.

6. Apparatus as claimed in any preceding claim wherein the immersion member has a free end arranged to be supported in said liquid storage volume of the storage tank.

Claims

7. Apparatus as claimed in any preceding claim wherein said aperture is provided in a sidewall of the immersion member.

8. Apparatus as claimed in claim 6 or claim 7 wherein said aperture is provided at said free end of the immersion member.

9. Apparatus as claimed in any preceding claim wherein a plurality of apertures are provided in the immersion member.

10. Apparatus as claimed in any preceding claim wherein the immersion member is provided in a generally upright orientation, the pressure signal device being arranged to measure a pressure of gas at a position of the immersion member above said aperture.

1 1 . Apparatus as claimed in any preceding claim operable upon a command by a user to force gas into the immersion member for a predetermined period of time.

12. Apparatus as claimed in any preceding claim operable to force gas through the immersion member substantially continuously.

13. Apparatus as claimed in any preceding claim arranged to force the gas through the immersion member at a prescribed flow rate.

14. Apparatus as claimed in any preceding claim arranged to measure the pressure of gas in the immersion member whilst gas is being forced through the immersion member.

15. Apparatus as claimed in any preceding claim arranged to measure the pressure of gas in the immersion member whilst gas is not being forced through the immersion member.

16. Apparatus as claimed in any preceding claim arranged to measure a pressure of gas in the immersion member whilst gas is substantially static in the immersion member.

17. Apparatus as claimed in any preceding claim wherein said gas is a gas drawn from said storage tank.

18. Apparatus as claimed in any one of claims 1 to 16 wherein said gas is drawn from an outside of the storage tank.

19. Apparatus as claimed in any preceding claim wherein said gas comprises a nonflammable gas.

20. Apparatus as claimed in any preceding claim wherein said gas is provided under pressure from a gas storage volume.

21 . Liquid gauge apparatus comprising: an immersion member comprising a hose member having a passageway provided therethrough, the immersion member having an entrance aperture at a first position of the passageway, the entrance aperture being provided in fluid communication with a gas supply, and an exhaust aperture at a second position of the passageway axially displaced from the first position, a gas pressure signal device having a gas pressure sensor arranged to measure a pressure of gas at said entrance aperture, the pressure signal device being configured to provide an output corresponding to a difference between a gas pressure at the entrance aperture and a reference pressure, wherein the immersion member is configured to be supported with at least a portion of the immersion member within a liquid containment volume of a liquid storage tank, the apparatus being further configured to force a gas from said gas supply through the passageway from the entrance aperture to the exhaust aperture, the hose member being configured such that a dimension of the portion of the passageway provided by the hose member may be enlarged from a first value to a second value against a pressure of liquid in the liquid storage tank in which the immersion member is immersed by forcing gas from the gas supply through the entrance aperture.

22. Apparatus as claimed in claim 21 wherein a gas flow restrictor is provided between the gas supply and the entrance aperture of the immersion member.

23. Apparatus as claimed in claim 21 or 22 wherein the immersion member comprises a lay-flat hose member.

24. Apparatus as claimed in any one of claims claim 21 to 23 wherein the immersion member comprises a polymeric material, preferably polythene.

25. Apparatus as claimed in any one of claims 21 to 24 wherein the immersion member is arranged such that the entrance aperture is located below the exhaust aperture.

26. Apparatus as claimed in any one of claims 21 to 24 wherein the immersion member is arranged such that the entrance aperture is located above the exhaust aperture.

27. Apparatus as claimed in any one of claims 21 to 26 arranged whereby at least a first portion of the immersion member is provided above a second portion of the immersion member, the first portion being axially spaced apart from the second portion.

28. Apparatus as claimed in claim 27 wherein the first portion is substantially vertically above the second portion.

29. Apparatus as claimed in any one of claims 21 to 28 whereby at least a portion of the immersion member is provided in the liquid containment volume in a substantially horizontal plane.

30. Apparatus as claimed in any one of claims 21 to 29 configured to discharge gas emerging from the exhaust aperture inside the liquid storage tank.

31 . Apparatus as claimed in claim 30 configured to discharge gas emerging from the exhaust aperture inside the liquid storage tank above an upper limit of the level of liquid in the storage tank.

32. Apparatus as claimed in any one of claims 21 to 29 configured to discharge gas emerging from the exhaust aperture outside the liquid storage tank.

33. Apparatus as claimed in any preceding claim wherein the gas comprises at least one selected from amongst a non-flammable gas, nitrogen, argon and air.

34. Apparatus as claimed in any preceding claim wherein the apparatus comprises a controller configured to receive and to store: a pressure data value corresponding to a pressure level input signal from said gas pressure signal device; and a quantity data value corresponding to an input by a user of a quantity of liquid contained in the liquid storage tank.

35. Apparatus as claimed in claim 34 configured to calculate a density value corresponding to the density of liquid contained in the liquid storage tank based on said pressure level input signal and said quantity value.

36. Apparatus as claimed in claim 35 further configured to receive an input from a user of a liquid type corresponding to the type of liquid that has been added to the storage tank.

37. Apparatus as claimed in claim 36 further configured to compare the density value with a density reference value corresponding to the liquid type input by the user, the apparatus being further configured to determine whether the density value corresponds to the density reference value.

38. Apparatus as claimed in claim 37 configured to request a user to re-enter at least one selected from amongst said quantity value and said liquid type if said density value does not correspond to the density reference value.

39. Apparatus as claimed in claim 37 or 38 wherein if the density value does not correspond to the density reference value the apparatus is configured to determine a proposed liquid type being a type of liquid having a density corresponding to the density value and to request a user to input a confirmation whether or not the liquid added by the user corresponds to the proposed liquid type.

40. Apparatus as claimed in any one of claims 36 to 39 configured to determine whether the pressure data value and the quantity data value are consistent with one another based on the input by the user of the liquid type.

41 . Apparatus as claimed in claim 40 configured to request a user to re-input at least one selected from amongst said quantity value and said liquid type if said particular values of pressure data value and quantity data value are not consistent with the input by the user of the liquid type.

42. Apparatus as claimed in claim 40 or 41 wherein if said particular values of pressure data value and quantity data value are not consistent with the input by the user of the liquid type the apparatus is configured to determine a proposed liquid type being a type of liquid for which the pressure data value and quantity data value are consistent and to request a user to input a confirmation whether or not the liquid added by the user corresponds to the proposed liquid type.

43. Apparatus as claimed in any one of claims 34 to 42 wherein the controller is provided with a lookup table comprising a plurality of respective different quantity data values and corresponding pressure data values for each of a plurality of liquids that are to be stored in the storage tank.

44. Apparatus as claimed in any preceding claim wherein said tank is provided with a pressure release valve arranged to prevent a pressure of gaseous fluid in the tank exceeding a critical value.

45. Apparatus as claimed in any preceding claim wherein the liquid is a liquid fuel.

46. A liquid storage tank comprising apparatus as claimed in any preceding claim.

47. A vehicle comprising a liquid storage tank as claimed in claim 46.

48. A vehicle as claimed in claim 46 wherein the vehicle is a road tanker.

49. A tanker for transporting hydrocarbon based liquid comprising apparatus as claimed in any one of claims 1 to 45.

50. A method of measuring a level of liquid in a storage tank comprising: providing liquid gauge apparatus according to any one of claims 1 to 45; immersing at least a portion of the immersion member in a liquid; and measuring a pressure of gas in the immersion member.

51 . Apparatus substantially as hereinbefore described with reference to the accompanying drawings.

52. A liquid storage tank substantially as hereinbefore described with reference to the accompanying drawings.

53. A vehicle substantially as hereinbefore described with reference to the accompanying drawings.

54. A tanker substantially as hereinbefore described with reference to the accompanying drawings.

55. A method substantially as hereinbefore described with reference to the accompanying drawings.