IES990837A2 - Improved method and apparatus for securely adding an additive to a fluid - Google Patents

Abstract

The method and apparatus of the invention may be used to add additive, such as dye, to a fluid such as fuel, by means of a pump (8) and a duct (4,5) through which the fuel flows. The pump (8) is operable to add dye to the fuel in discrete or regularly varying amounts. A light beam is generated by light emitter (16), enters inspection chamber (12) where the dye is added and exits the chamber (12) where it is received by external receiver (17). The light emitter (16) and receiver (17) are connected to a light sensor (15) which is operable to detect one or more types of change in a characteristic of the light beam when it is passed through the fuel. <Figure 1>

Description

IMPROVED METHOD AND APPARATUS FOR SECURELY ADDING AM ADDITIVE TO A FLUID The present invention relates to an improved method and apparatus for adding an additive to a fluid in a secure manner. The invention relates particularly, but not exclusively, to a method and apparatus for adding dye additive or marker, henceforth referred to as dye, to a fluid in a secure manner where fluid is dispensed from a delivery means which is required to deliver fluid with and without the dye.

Adding in a secure manner refers to the prevention or detection of errors in the way the dye is added to the fluid, including errors such as malfunction of the apparatus or of deliberate op accidental unauthorised interference, or of matters which might allow the intended purpose of the dye to be circumvented '· The invention also relates particularly, but not exclusively, to a delivery means which is a tanker truck and to a method for securely adding dye to fuel oil by apparatus on the truck. Fuel oil includes heating oil, diesel and gasoline and is henceforth referred to as fuel.

Many authorities charge different rates of tax on fuel depending on the purpose for which it is used, typically fuel for road use is taxed while fuel for heating or agricultural use is not taxed. Where the authorities specify that untaxed fuel be dyed with a coloured dye additive, it is important that the dyeing process is carried out in a secure manner which prevents the possibility of the intended taxation being avoided, either deliberately or accidentally, and which facilitates the system being monitored to ensure accurate and consistent dyeing of the fuel.

CA 2,168,149 discloses a method and apparatus intended for secure adding and dispensing of dyed and undyed fuel from a tanker truck where the fuel is dyed by apparatus on the truck. Dye is added at the end of the delivery hose through an inner hose within the delivery pipe and hose. The inner hose is fitted with a check valve at its end. This allows the system to deliver dyed or clear fuel without introducing dyed fuel into the delivery pipe or hose and thereby overcomes the problem of cross contamination when the delivery is changed from dyed to undyed fuel or vice versa. Dye is steadily pumped into the delivery system when a dyed delivery is carried out and the relative proportion of dye to fuel is regulated by a metering block which is manually set by trial and error and then sealed. No means is disclosed for monitoring the dye adding process or the flow of fuel.

W097/30930 also discloses a method and apparatus intended for secure adding and dispensing of dyed and undyed fuel from a tanker truck where the fuel is dyed by apparatus on the truck. In this instance dye is introduced by means of a piston injection pump and its output is mixed into the fuel flow by a blending device. The dye adding process is monitored by a flow sensor on the pipe connecting the injection pump to the blending device. The sensor relies on detection of the movement of a member in a close bore being lifted by the pulse from the injection pump and falling back under gravity. The dye tank is provided with an anti flush section and anti draining means to inhibit substitution of dye by a spurious fluid which would not be detected by the flow sensor. No means is disclosed for monitoring the flow of fuel through the apparatus.

The present invention provides a method of securely adding an additive to a fluid characterised by adding an additive to the fluid in discrete or regularly varying amounts; passing a light beam through the fluid; a characteristic of the light beam being altered by the relative proportion of additive in the fluid, one or more types of change in the characteristic of the light beam being sensed and used to indicate that additive is being added to the fluid in a secure manner, and where a detection of a change in the characteristic of the light beam is used to indicate the relative condition of the fluid and additive.

The relative condition of the fluid and the additive includes but is not limited to the following: additive has been added to the fluid and/or flow is taking place in the fluid and/or the fluid has not already had additive added and/or additive has been added to the fluid and a detection of an opposite change in the characteristic of the light beam is used to indicate that flow is taking place in the fluid and/or that the fluid has not already had additive added.

Optionally all or a portion of the discrete or varying amount of added additive is added into an inspection region of the fluid through which fluid is flowing and the additive added to the inspection region is transported from the inspection region by the flow of fluid.

Optionally the additive is dye.

Optionally adding of the discrete or varying amount of additive is repeated in a cycle Optionally adding of the discrete or varying amount of additive is repeated in a cycle corresponding to pulses from an injection pump.

Optionally the characteristic is light intensity.

Optionally the characteristic is light intensity and a detected decrease in intensity is used to indicate that additive has been added and a detected increase in intensity is used to indicate that flow is taking place in the fluid and/or that the fluid has not already had additive added.

Optionally the characteristic is light intensity and light of a colour which will be absorbed by the additive is used. Advantageously, the additive is of a substantially subtractive complementary colour to the colour of the light used.

Optionally the characteristic is light colour.

Optionally the characteristic is light colour and a detected increase in colour is used to indicate that additive has been added and a detected decrease in colour is used to indicate that flow is taking place in the fluid and/or that the fluid has not already had additive added.

Optionally all or substantially all of the portion of additive added into the inspection region is transported from the inspection region before the next portion of additive is added into the inspection region.

Optionally fluid enters the inspection region from opposing directions, one substantially in the direction of the entry of the light beam and the other substantially in the opposite direction to the exit of the light beam, such that fluid flow is away from the entry and exit of the light beam.

Optionally the light path is substantially horizontal.

Optionally the light path is relatively long or several times the length of the exit path of fluid from the inspection region.

Optionally a comparison measurement is made between two events, one being a known time and the other being a time when a change is detected in the characteristic of the light beam and the comparison measurement is compared to a reference measurement.

Optionally the reference measurement is derived from some average of previous measurements.

Optionally a comparison measurement is made of the length of time between two events, one being a known time and the other being a time when a change is detected in the characteristic of the light beam and the comparison measurement is compared to a reference measurement.

Optionally a comparison measurement is made of the amount of fluid flowing between two events, one being a known time and the other being a time when a change is detected in the characteristic of the light beam and the comparison measurement is compared to a reference measurement.

Optionally adding of the additive to the fluid is monitored to detect breaches of security and detection of such breaches activates responses such as warnings, creation of records or prevention of further adding of additive to the fluid.

The present invention also provides an apparatus for securely adding additive to a fluid in a secure maimer, the apparatus comprising an adding means and a duct through which the fluid flows, characterised in that the adding means is operable to add additive to the fluid in discrete or regularly varying amounts and a sensing means is provided which is operable to detect one or more types of change in a characteristic of a light beam when the light beam is passed through the fluid, Optionally an inspection chamber is provided on the duct, and the apparatus is provided with means to add all or a portion of the discrete or varying amount of added additive into the inspection chamber.

Optionally the additive is dye.

Optionally additive is added to the inspection chamber through a check valve.

Optinally the check valve comprises an elastic tube sleeved over a tube with an opening, where the opening conveys dye into the inspection chamber, and where the elastic tube is operable to lift off the opening under the action of higher liquid pressure within the tube.

Optionally the elastic tube covers the opening in the tube and one of its ends is adjacent to the opening in the tube.

Optionally the adding means is an injection pump which delivers discrete pulses of additive.

Optionally the duct comprises part of a delivery means.

Optionally the apparatus additionally comprises a controller, such as a PLC, which is operable to control or monitor the operation of the adding means and/or the sensing means.

Optionally the controller and sensing means are operable to detect breaches of security and on detection of such breaches the controller is operable to activate responses such as warnings, creation of records or prevention of further adding of additive to the fluid.

Optionally the sensing means comprises a light emitter, a light receiver and an electronic light sensing means, such as a photodiode, and optionally optic fibres connect the light emitter and light receiver to the light sensing means.

Optionally the light sensing means senses changes in light intensity or alternatively, the light sensing means senses changes in colour.

Optionally the light sensing means includes a photodiode.

Optionally the light emitter emits light of a colour which is absorbed by the additive.

Optionally, the light emitter is arranged such that the dye is of substantially subtractive complementary colour to that of the light emitted.

Optionally the light sensor is of the type where a target or threshold switching level can be set.

Optionally the inspection chamber is provided with one or more windows through which the light beam enters and exits.

Optionally the volume of the inspection chamber is less or significantly less than the volume of fluid which flows through it over the period of time between successive occurrences of additive being added.

Optionally the inspection chamber is internally arranged to avoid stagnant regions of fluid flow or alternatively, the inspection chamber is internally arranged to give differential flow.

Optionally the duct conveying fluid into the inspection chamber is divided into two inflow ducts which flow into substantially opposing ends of the inspection chamber and fluid is conveyed through a single exit out of the inspection chamber.

Optionally the light path in the inspection chamber is substantially horizontal.

Optionally the distance between windows in the inspection chamber is relatively long or several times the length of the exit path of fluid from the light path to the exit from the inspection chamber.

Optionally the apparatus includes a fluid flow meter which provides electronic pulses at a rate in proportion to fluid flow and the controller determines the amount of fluid which has flowed between two events by counting the number of these pulses.

The apparatus also provides a means for blending additive into the fluid where additive is added in discrete or regularly varying amounts, comprising an elongate main chamber through which fluid passes, a manifold extends along the main chamber and delivers additive into the fluid by delivering it along the length of the main chamber through a plurality of openings, the volume of the main chamber being at least equal to the volume of fluid flowing between the events of additive being added characterised in that the manifold communicates with an apparatus operable to detect one or more types of change in a characteristic of a light beam when the light beam is passed through fluid in an inspection chamber and/or all or part of the manifold comprises a tube and one or more of the openings in the manifold is provided with a check valve which comprises an elastic tube sleeved over the manifold tube in the region of the opening and which is operable to lift the elastic sleeve off the opening under the action of higher liquid pressure within the manifold Optionally the elastic tube covers the opening in the manifold and one of its ends is adjacent to the opening in the manifold.

Optionally the fluid is dye.

The invention will now be described more particularly with reference to the accompanying drawings, which show by way of example only, an embodiment of an apparatus according to the invention which securely adds dye to fuel when required. The apparatus is shown connected to the delivery system of a tanker truck which is required to deliver fuel with and without dye added.

Figure 1 and Figure 2 show sectional views of the apparatus in diagrammatic form. The dashed lines represent electronic, electrical or pneumatic connections The following is an index of the reference numerals used in Figure 1 :- 1. Fuel flow meter. 2. Fuel delivery pipe. 3. Fuel delivery nozzle. 4. Local flow inlet duct.

. Local flow outlet duct. 6. Isolating valve. 7. Dye tank. 8. Injection pump. 9. Dye line.

. Controller. 11. Sealed cabinet. 12. Inspection chamber. 13. Inspection chamber dye outlet. 14. Local flow duct division.

. Light sensor. 16. Light emitter. 17. Light receiver. 18. Blender. 19. Blender main chamber.

. Blender manifold. 21. Manifold outlets.

Referring to Figure 1, there is shown part of the delivery system of a fuel tanker truck, including the fuel flow meter 1, a section of the fuel delivery pipe 2 downstream of the flow meter 1 and the fuel delivery nozzle 3. Undyed fuel is stored in the truck tank compartments and is pumped to the delivery nozzle 3 via the fuel flow meter 1 and delivery pipe 2. The delivery system also comprises a flexible hose and reel between the nozzle 3 and section of delivery pipe 2 which is not shown in the figure. Some delivery systems, again not shown in the figure, comprise two nozzles and two flexible hoses and reels, one set being dedicated to dyed fuel and the other to undyed fuel.

Dye is pumped into the delivery system in a two stage process when dyed fuel is required. In the first stage, the dye is added to a flow of fuel in a duct, comprising a parallel flow of the delivered fuel, in precise direct ratio to the flow measured by the main truck delivery meter. In the second stage, the duct or parallel flow rejoins the main flow to give the correctly blended dyed product. The flow of fuel into which the dye is added is termed the local flow of fuel. In the preferred embodiment, the parallel flow is the local flow. In alternative applications, the parallel circuit is omitted and dye is added directly into the main flow of fluid.

Local flow takes place in a parallel circuit duct comprising an inlet pipe 4 and outlet pipe 5. Flow in the delivery pipe gives rise to a pressure drop between the inlet and outlet points on the delivery pipe 2 and promotes flow in the local flow duct 4,5 when an isolating valve 6 on the circuit is open. The isolating valve 6 is opened or closed when a delivery is required as dyed or undyed, respectively.

The first stage comprises a dye tank 7 for storing the dye and an injection pump 9 which injects discrete quantities of dye into the local flow. The injection pump 8 is an air -driven piston and plunger type with inlet and outlet non-retum valves. The system uses dye in a highly concentrated formulation. A blender 18 mixes the dye with the fuel in the local flow.

The system is provided with an electronic controller, such as a PLC (programmed logic controller), computer or microprocessor 10, henceforth referred to as the controller, which monitors and controls the operation and security of the dye adding process. The fuel flow meter 1 is provided with an electronic pulse output which delivers pulses to the controller 10 in proportion to the flow of fuel passing through it.

The principal components of the apparatus are located in a secure sealed cabinet 11 which can only be accessed by authorised personnel.

An aspect of the invention is that when dye is added to the fluid it is deliberately added in discrete or varying amounts in order that changes in light transmitting characteristics can be detected in the resulting mixture of dye and fluid. A piston plunger type injection pump delivering discrete amounts of dye in a repeating cycle is conveniently used to provide the required changes. The process of dye addition can then be verified by checking that the light characteristics are appropriately altered when dye is added and that flow is taking place by checking that the light characteristics are restored to the status they had prior to dye being added. The method continuously checks its own ability to detect the dyed and undyed characteristics. The check related to fuel flow also checks against the possibility of dye being injected into a stationery mass of fuel while undyed fuel was being diverted elsewhere.

The operation of the dye adding process is sensed by an apparatus comprising an inspection region of the fluid within an inspection chamber 12 positioned on the local flow and an inspection means comprising a light sensor. The apparatus allows a light beam to be emitted and received through a path in the fuel flowing through the inspection chamber 12.

A portion of the dye pulse from the injection pump 8 and dye line 9 is ducted into the inspection chamber 12 and enters the light path of the light beam, either directly or mixed with the flowing fuel. The dye is then carried out of the inspection chamber by the local flow of fuel, causing the strength of the mixture of dye and fuel in the inspection chamber to revert to fuel without dye.

In a preferred embodiment, a light beam is generated by an emitter 16 which is external to the chamber 12 and enters it through a small window at one end. The beam exits through a second small window where it is received by an external receiver 17. The emitter 16 and receiver 17 are connected to a light sensor 15 by means of optic fibres.

In an alternative arrangement, the light beam is reflected by a target or by a reflector within the inspection chamber and exits back out through the same window through which it entered the inspection chamber. This arrangement doubles the length of the light path for a given length of inspection chamber and makes both optic fibre ends accessible from the same end of the apparatus. However, the received light beam may become too weak where a target or multiple faceted reflector is used. A stronger reflected beam can be achieved by using a simple reflecting surface, but alignment of the beam to the receiver may become more difficult.

The inspection chamber is arranged such that dye is introduced into the light path when an injection stroke occurs and is rapidly removed from the chamber following the injection stroke. This is achieved by arranging the inspection chamber to be such that its volume is less or significantly less than the volume which flows through the inspection chamber over the period of time between injection pump strokes and by arranging the geometry to avoid stagnant regions in the chamber where dye might remain trapped from one injection stroke to the next.

In a variation of the invention, the geometry is arranged to give some degree of differential flow in the inspection chamber, with some regions flowing faster than others. The reason for this is to allow a more gradual removal of dye from the inspection chamber and thereby allow a qualitative measure of the process to be carried out. This is discussed in greater detail later in the specification.

In the preferred embodiment, the apparatus is provided with a fuel inlet division 14 where the inflow of fuel is divided into two inflow channels which flow into opposite ends of the inspection chamber 12, are reunited in the chamber 12 and exit from one point. The light path enters at one inflow channel, substantially in the direction of flow, and exits at the other inflow channel, substantially against the direction of flow. This arrangement provides several advantages.

Firstly, it keeps dye away from the lenses or windows through which the light beam is emitted and received, and thereby reduces the possibility of staining or contamination or any other undesirable effect which might arise from direct contact with the dye.

Secondly, it allows the dye outlet 13 to be positioned close to the exit from the light path, thereby allowing the dye to clear rapidly from the light path following the injection stroke. Thirdly, it prevents the possibility of dye being temporarily retained in regions of slow or stagnant fluid movement, such as at regions or crevices close to the lenses or windows, Fourthly, it allows a relatively long light path through the inflowing base fluid without compromising the need to rapidly clear dye from the light path, and thereby allows the possibility of improved inspection of the incoming fuel.

In the preferred embodiment, the light path is arranged to be substantially horizontal. This has the following advantages. Firstly, it reduces the risk of contamination of the windows by debris or settlement of suspended matter under the influence of gravity. Secondly, it reduces the risk of air or gas pockets arising or being trapped adjacent the windows. Such pockets could affect the light path or could promote contamination of the windows by allowing drying out, filming or other reaction to occur which would not take place if the window remained submerged.

The apparatus further comprises a means for emitting and receiving the light beam. The apparatus is operable to detect a change in the received light beam which has passed through the inspection chamber when the fuel is uncoloured and when it is coloured by the dye.

The detected change may be a change in the intensity or energy of the light or a change in the colour or hue of the light. The dye alters the light passing through the dyed fuel by absorption and by reflection. These changes can be detected or measured with electronic light sensors. Light sensors which detect changes in light intensity tend to be simpler and less expensive than those which detect changes in colour. However, those which detect changes in colour have the relative advantage that they are less sensitive to contamination of the lens or windows required with optical equipment, and are less sensitive to changes in the colour or other characteristics of the fuel.

Light sensors are available in various forms, including photodiode and photoresitor types. Light sensors are also available in packaged form where a target or threshold value can be set for the light characteristic and where an on or off output is signalled when the target value is reached. A photodiode light sensor of this type is used in the preferred embodiment of the invention. These types are commonly used for solid object detection in industrial applications and are accordingly inexpensive. Alternatively, the output can be of the analogue type where the signal is proportional to the relative strength of the sensed characteristic of the right. This can have advantages when qualitative monitoring of the dye adding process is required. However, it has the relative disadvantage that many controllers are not capable of processing analogue signals without the addition of further equipment.

When the apparatus is in operation, the signals from the light sensor are monitored by the controller 10. The controller checks that dye injection has taken place by detecting a reduced or off signal immediately following the injection stroke. The controller checks that fuel is flowing in the inspection chamber by detecting the re-establishment of the signal following the reduced or off signal arising from the injection stroke. The controller can be programmed to take appropriate action if dye injection or the flow of fuel is not detected or is inadequate.

Detection of the injected dye pulse is relatively straightforward with the method of the invention because the pulse is highly concentrated and is quite opaque when injected before mixing with the undyed fuel. Detection of the absence of local flow is also straightforward because the opaque mixture will not clear between one injection stroke and the next if local flow is absent.

A local flow rate of inadequate magnitude can also be detected by the method of the invention by using the apparatus to measure the length of time taken for the opaque mixture to clear to a known state and by comparing its length of time to an expected value which has been predetermined by means such as trial and error.

Care must also he taken to ensure that false readings are not caused by discoloration or gradual build up of contaminants on the windows or the light sensor lenses.

The apparatus of the invention can also be used to check the incoming fuel, in particular to check that it has not already been dyed. The detection of possible double dyeing of fuel can be important where it is necessary to prevent a particular type of fraud related to recirculating the fuel through the dye adding apparatus. Accurate detection of the dyed status of the incoming fuel is more difficult than detection of the concentrated dye pulse because the mixture is not opaque and the differences to be measured are much less pronounced. In the preferred embodiment, the length of travel of the light beam through the fuel is deliberately elongated to increase the degree of absorption of the light by the dye. The degree of absorption of the light varies exponentially with the length of the light path and the concentration of the dye in the fuel. The length of the light path is defined as its length in the fuel or fuel and dye mixture. The light path is arranged relatively long in relation to the length of the exit path of fluid from the inspection region, its length being several times the length of the exit path. The controller is programmed to take appropriate action if a reduced or off signal is detected at times other than following the injection stroke.

Detection of double dying or colour in the incoming fuel can be facilitated in several ways One method is to use a light sensor which detects colour rather than light intensity. An alternative preferred method uses a light sensor which detects light intensity but with an emitter or light source of a colour which is preferentially absorbed by the dye. This is achieved by using a light source of a colour such that the dye is of a substantially subtractive, complementary colour, for example a green light source is ideally used with red dye, a blue light source with yellow dye and a red light source with blue dye. Where a green light source is used where the dyed fuel colour is red and the undyed fuel varies from clear to light amber, the green light source is more readily absorbed by a red than an amber medium and is thus more sensitive to dye in the fuel than it is to the degree of amber of the base fluid or to light contamination or yellowing of the window. Light other than visible light can also be used with the method of the invention As mentioned previously, the detection of a regularly changing characteristic has the additional advantage that the apparatus is continually checking itself. For example, if dedicated light sensors were used to detect the condition of fuel in a part of the apparatus where it was expected to be always dyed or always undyed, a steady false signal could readily occur which incorrectly indicated the fuel condition, either by deliberate misuse of the system or by accidental malfunction, such as contamination of the light sensor windows or lenses, blockage of the light emitter, or failure or override of the light sensor itself.

In addition to monitoring the discrete parameters mentioned above, the apparatus can also be used to qualitatively monitor the dye additive process by measuring the time taken or the amount of fuel passing through the fuel flow meter while the light sensor signal changes from one state to another and then comparing the result to a known value or to a running average value. This approach can be used to obtain comparative or qualitative information on the colour of the incoming fuel, the approximate volume of the injection stroke of the approximate rate of flow of fuel through the inspection chamber.

For example, the controller may count the number of electronic pulses received from the fuel flow meter over the interval between the injection stroke and the light sensor detecting the light intensity reverting to a value preset on the sensor. This preset value may be the chosen threshold value at which the sensor is set to distinguish between dyed and undyed incoming fuel. The controller may keep a running average of these numbers and identify any newly recorded number which significantly differs from the running average. By maintaining a record of this information, electronic or otherwise, a qualitative audit trail is created for the incoming fuel which can be readily cross referenced to customer deliveries. This could be used, for example, to determine a history of partial recirculation of fuel through the dye adding apparatus, where the partial recirculation resulted in a mixture which was sufficiently weak in colour not to have been detected by the normal threshold setting value on the light sensor.

Light sensors are sometimes provided with a separate output which indicates that the light intensity lies within a set range of the threshold value over a given period of time to give warning of a potential unstable output. This output may also be used to provide an alternative qualitative monitoring of the dye adding process similar to that already described. For example, the controller may count the number of electronic pulses received from the fuel flow meter whilst the unstable output is active. The number will increase as the average light intensity condition gets closer to the threshold value.

The use of a running average assists in eliminating the effect of gradually changing conditions which might otherwise cause misleading results, such as gradual build up of contamination on the windows, seasonal changes in operating conditions or wear in the apparatus.

The use of qualitative checks has the additional advantage that it further increases the difficulty of unauthorised interference, because manual simulation of the qualitative results would be more difficult than manual simulation of simpler on and off signals.

Usually, detection of the threshold value will cause a response such as a shut down of the apparatus and it is important that the threshold value is set sufficient high that the response is not unnecessarily activated, for example by the coincidence of several contributing factors such as an extreme in a normal operating condition, use of unusually dark but undyed fuel or minor contamination of the windows or lenses.

The controller is programmed to detect when breaches of security occur and on detection of such breaches it is additionally programmed to activate appropriate responses such as the prevention of further adding of dye to the fuel by shutting down the apparatus. The responses may also comprise the creation of records of the breaches and warnings to the operator or warnings communicated back to the fuel distributor's base. The appropriate level of responses will usually be determined by the authorities and the fuel distributor.

The invention presents many advantages over the prior art methods in addition to those already discussed.

The invention presents the additional advantage that it provides a direct confirmation that the fuel has been coloured. This contrasts with the prior art methods which disclose no means of providing such confirmation. However, one prior art method attempts to inhibit substitution of dye by a spurious uncoloured fluid by providing the dye tank with an anti flush section and an anti draining means.

The invention also presents the advantage that it provides a direct confirmation that dye has been delivered into the fuel. This again contrasts with the prior art method which only provides an indirect confirmation by checking that a liquid pulse has taken place in the pump. There remains the uncertainty that the pulse might be deliberately or accidentally diverted before reaching the flow of fuel.

The invention presents the further advantage that it checks the flow of dye independently of temperature induced viscosity effects, This contrasts with the prior art which relies on detection of the movement of a member in a close bore being lifted by the pulse and falling back under gravity. Changes in viscosity may affect whether the member is lifted or whether it returns under gravity.

The invention presents the additional advantage that it checks the flow of dye with equal reliability for pulses of large or small volume. This again contrasts with the prior art which relies on detection of the movement of a member in a close bore being lifted by the pulse and falling back under gravity. This method cannot be reliably used with very small pulses. The use of very small pulses is of considerable importance where it is desired to use a highly concentrated dye.

The invention also presents the advantage that it checks that local fuel flow is taking place when the flow rate is very low compared to the normal flow rate. The prior art discloses no method for detecting such low local fuel flow. The detection of the movement of a member in a close bore being lifted by the pulse and falling back under gravity, as disclosed for dye flow, would not work where flow was required to be measured at rates which are very low relative to the normal maximum flow rate. Such low rates are required, for example, when foaming takes place in a tank or when a fill is being completed and there is no ready indication of fuel level.

The invention presents the further advantage that the apparatus has no moving parts, In additional to general long term reliability, this also avoids the possibility of misreadings caused by movement such as truck engine vibrations.

The invention presents an additional advantage where safety reasons require that electrical or electronic components in contact with fuel or dye meet safety requirements, such as explosion proof requirements. Such requirements can restrict the types of components that can be used or can increase their cost. The optic fibre connections, used in the apparatus of the invention, permit the electrical and electronic components, including the light sensor, to be positioned remotely from the inspection chamber and all points of potential contact with the fuel or dye. The light emitting and light receiving ends of the optic fibres are not electrical or electronic devices.

The apparatus also includes a blender 18 which comprises an elongate blender main chamber 19 which is connected in line with the parallel circuit 4,5 and a blender manifold 20. Dye is pumped into the blender manifold 20 by the injection pump 9 which delivers discrete amounts of dye in a preset proportion to the amount of fuel passing through the fuel flow meter 1. The blender manifold 20 spreads the injection pulse along the length of the main chamber 19.

The cross sectional area of the main chamber 19 is arranged such that the average time for the flow of fuel to pass through it is greater that the interval between injections from the injection pump 8. This ensures that all of the fuel is dyed as it passes through the main chamber 19. In the preferred embodiment, the cross sectional area is arranged such that two or three injections take place over the average time for the fuel to pass to ensure overlap of the elongated injections from the blender manifold 20 and thereby promote more even mixing of the dye and fuel.

Referring again to Figure 1, the inspection chamber outlet 13 and the manifold outlets 21 are shown as holes in the dye line 9 and blender manifold 20. These holes are made relatively small to ensure reasonably even flow from them when injection takes place. The resistance to fluid flow through the holes should be relatively high compared to the resistance to fluid flow through the tube bores connecting the dye line to the holes. The openings in the manifold tube are arranged such that leakage into or out of them is prevented in the intervals between injections. Such leakage could be caused by the pressure gradient along the blender chamber caused by the flow of fuel. It could also be caused by differences in density between the dye and fuel.

Figure 2 shows a preferred embodiment of the invention, where the holes 100 are additionally provided with check valves 101 to prevent leakage. The check valves 101 comprise short lengths of elastic tube 102 fitted over the dye bearing tube or manifold 9,20 with one end of the elastic tube 102 covering the hole 100. The elastic tube is held in position by a clip 103 which is located away from the hole 100. Dye under pump pressure can readily lift the elastic tube and escape into the inspection chamber 12 or main chamber 19. However, dye under low pressure is retained. Reverse flow into the dye bearing tube 9 or manifold 20 is prevented by the elastic tube 102 covering the holes 100.

Referring again to Figure 1, the inspection chamber dye outlet 13 is shown in diagrammatic form located on a continuation of the dye line 9 connecting to the blender manifold 20. In practice, the dye outlet 13 may be located in alternative arrangements such as at the distal end of the connected dye line 9 and blender manifold 20 or on a separate tee-ed off branch line extension of the dye line 9 with its distal end closed. These alternative arrangements may be found more convenient for positioning the outlet 13 in the inspection chamber 12 or for checking or servicing the check valve.

The following arrangements provide an example of the apparatus of the invention where dye is to be added to fuel flow delivery rates varying over a range of 5-350 litres per minute and where fuel to dye concentration is 35,000:1 and the dyed fuel is coloured red.

The injection pump delivers a pulse of 1.4 ml of dye. The inspection chamber is 8 cm in length between the light sensor windows. The blender main chamber is 40 cm in length and 24 cm2 in cross sectional area. The manifold runs almost the full length of the mam chamber and comprises a tube which is 5 mm in outer diameter and 2-3 mm in internal diameter. The tube conveying dye into the inspection chamber is of the same profile.

There are three to four equally spaced apart holes in the manifold and one in the inspection chamber. The holes are 0.7 mm in diameter. The elastic tubes covering the holes have a free internal diameter slightly less than the outer diameter of the manifold and have a wall thickness of 1.5 mm and a length of 20 mm.

The light sensor is an electronic through beam photodiode type in packaged form with a settable target or threshold setting and an on or off type output. The emitter and receiver ends are connected to the sensor housing by optic fibres. The light source is an LED producing monochromatic visible green light. The emitter and receiver are provided with focusing lenses which are mounted adjacent glass windows in cavities sealed to prevent ingress of dust or contaminants. One side of each window makes contact with the fuel contents of the inspection chamber.

It is to be understood that the invention is not limited to the specific details described above which are given by way of example only, and that various modifications and alterations are possible without departing from the scope of the invention.