SECURITY DEVICE

TECHNICAL FIELD

This invention relates to a security device. BACKGROUND ART

Hydraulically operated machines are commonplace, especially in heavy construction machines and throughout industry. Construction machines in particular tend to be very large and often require specially adapted trailers in order to transport them from one place to another. As a consequence, despite their capital value, they are often left unattended on construction sites. Unauthorised operation of the machines, including theft, is a major concern.

It is therefore highly desirably to provide a tamper proof security device such that unauthorised operation or theft of these machines is severely limited if not completely prevented. A technique for rendering a hydraulic circuit inoperable is to install a valve which is capable of switching the flow of hydraulic fluid from a normal operating state into an inoperable state.

It is often convenient to place the valve in the pilot circuit of the machine. The pilot circuit consists of a pilot pump and filter which provides primary pressure to a pilot valve which in turn directs pressure to the main hydraulic circuit.

The pilot pump operates whenever the engine of the machine is going. For this reason immobilising the machine by blocking the pilot circuit is not an option as serious damage would occur due to a build up of pressure if the engine was started while the pilot circuit was blocked. By installing the security valve in the pilot circuit between the pilot pump and the pilot valve it is possible to divert flow away from the pilot valve and back to the tank, thus disabling the pilot circuit and consequently the main hydraulic circuit.

A disadvantage with this simple arrangement is that unauthorised operation may still be possible by switching the valve back into a normal operating position, or by bypassing the valve by removing it from the circuit followed by direct reconnection of the pilot circuit.

Various techniques have been suggested to overcome this problem. For example JP 09050584 A2 discloses a solenoid valve placed into a pilot circuit between the pilot pump and the pilot valve such that operation of the solenoid valve requires input of an identification number into a keypad in order to unlock the circuit. In a similar fashion JP 2003130010 A2 discloses a solenoid valve installed in a pilot circuit together with a device which measures the inclination of the machine. This combination is set such that the angle of inclination of the machine exceeds a preset value the solenoid switch is activated and cuts off the flow of primary pressure in the pilot circuit. The machine can be prevented from being loaded onto a trailer by setting the angle of inclination at less than that required to traverse the ramp onto the trailer.

The main disadvantage with these techniques is that they require an electrical connection to the solenoid valve installed as a security device. This allows the security device to be located by tracing the electrical circuit from the key pad back to the valve. This may lead to the valve being isolated or unlocked by other means.

JP 2003278187 A2 discloses a mechanical system consisting of a change over valve connecting several remote control valves to a number of hydraulic actuators, such that the change over valve may be moved, and locked into a plurality of switching positions. In each instance the change over valve may be switched from an operating mode into a non-operating mode.

The main disadvantage with this method is that the configuration of the valve is complex, and therefore adds to the cost of installation, and depends on the make and type of machine to which it is fitted. It therefore is unsuitable as a technique which is generally applicable to all hydraulically operated machines.

JP 2003091435 discloses a switchable valve which may be locked by a key. In this instance the valve is located inside a valve housing containing the switching valves of the hydraulic circuit. This arrangement has the disadvantage that the valve is factory fitted to the machine as part of the overall switching valve module. As such this method also is not capable of being used on all hydraulically operated machines.

A disadvantage of these systems is that their installation requires considerable technical skill.

It would be desirable if there could be provided a security device for installation in

hydraulic circuits that is cost effective, tamper-proof, does not require specialist skills for installation, and may be retrofitted to any hydraulically operated machine.

GB 2334768 discloses a brake system for motorcycles including a security device attached to a brake calliper. The system is operated by pressurising the hydraulic brake line to engage the brake before screwing down a screw in the security device to block the hydraulic circuit, thus preventing release of the pressure. This locks the brakes until the pressure is released by loosening the screw.

The device of GB 2334768 cannot be used in a pilot circuit as in operation it blocks the hydraulic circuit rather than diverting the flow. As discussed above, blocking the pilot circuit would lead to serious damage to the pilot circuit if the pilot pump is switched on (eg., when the engine is switched on) when the device is blocking flow.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising ¹ is used in relation to one or more steps in a method or process.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice. Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided a security

device for installation in a pilot circuit of a hydraulically operated machine, the security device having a housing containing a cavity and a head, in which the head, when rotated, diverts the hydraulic flow of the machine into one of at least two modes of operation, characterised in that the top of the head is recessed into the cavity at a depth below a rim of the cavity, and a wall of the cavity is positioned in sufficient proximity to an external side of the head, such that rotation of the head requires application of a key which engages with the external side of the head.

Throughout this specification a security device should be understood to refer to any device which is used to enhance safety or to protect property from unauthorised use or procurement.

Throughout this specification reference to the pilot circuit should be understood to refer to a hydraulic circuit having a pilot pump and filter connected to a pilot valve. The pilot pump provides primary pressure to the pilot valve which in turn directs pressure to operate the main hydraulic circuit.

Throughout this specification a housing should be understood to refer to a rigid casing for containing functional elements of a device. Similarly, a cavity should be understood to refer to a hollow within a solid body, such as a housing.

Reference to a head throughout this specification should be understood to mean the distal section of a connecting rod, and a key should be understood to refer to an instrument for grasping and turning a head. In a preferred embodiment the security device includes a switching mechanism connected to the head.

This invention may be applied to any security device which includes a switching mechanism activated by rotation of a head. A switching mechanism may be any part or parts of a machine working together in order to alter the operational status of the machine.

The security device may include a switching mechanism which changes the electrical or mechanical status of the device.

In a preferred embodiment the switching mechanism is a valve.

In a preferred embodiment the switching mechanism directs fluid flow into one of at least two different modes of operation.

One of the modes of operation may be associated with a normal operational flow of the fluid.

Reference throughout this specification to a mode of operation associated with the normal operational flow should be understood to refer to flow in any hydraulic circuit that may be used to operate the machine.

Another of the modes of operation may be associated with a non-operational flow of the fluid.

Reference throughout this specification to a mode of operation associated with a non-operational circuit should be understood to refer to flow in any hydraulic circuit that diverts fluid from operation of the machine.

A security device of this kind has the considerable advantage that it may be installed in any hydraulic or pneumatic circuit and used to divert fluid flow so as to render the circuit inoperable.

In a preferred embodiment the housing is formed from aluminium.

Reference throughout this specification will be made to the housing as formed from aluminium. However, those skilled in the art will recognise that housings may be made from a variety of materials, for example steel, and reference to aluminium only throughout this specification should in no way be seen as limiting.

The advantage of using an aluminium casing is that it is a strong material which is not readily deformed yet may be cast or machined to obtain a desired shape. Furthermore, it provides a secure casing for the components contained within the housing. A further advantage may apply when the security device is to be attached to a machine on which aluminium components are common, thus reducing the likelihood of the device being detected.

Application of this invention requires that a cavity be formed within the housing to enable access to the head of the switching mechanism. In a preferred embodiment the cavity is a cylinder.

Reference throughout this specification will be made to the cavity being a cylinder.

However, those skilled in the art will recognise that other shapes of cavity may be used and reference to cylindrical forms only throughout this specification should in no way be seen as limiting.

The advantage of a cylindrical cavity is that it may be readily formed in the housing by machining or casting, and has parallel walls which allow access directly down the cylinder but limit access at an angle from the top.

The function of the cavity is to enable key access to a head attached to a switching mechanism.

In a preferred embodiment the head is shaped so that the sides of the head may engage with a key. The switching mechanism may be operated by rotation of the key while engaged with the sides of the head.

A shaped head has the added advantage that a range of different shapes may be used, necessitating a corresponding range of keys. This provides additional security against unauthorised operation of the device. Preferably the head is recessed into the cavity at a depth below the rim of the cavity sufficient to limit access to the head with common implements, such as pliers and screw drivers.

Preferably the sides of the head are in close proximity to the sides of the cavity such that common implements cannot engage with the sides of the head. The advantage of this aspect of the invention over the prior art lies in the increased difficulty in accessing the head in order to switch the operational mode of the device. The increase in difficultly is a result of a combination of the depth of the head below the rim of the cavity and the narrowness of the space between the sides of the head and the sides of the cavity. According to another aspect of the present invention there is provided a method of installing a security device into a pilot circuit having an inlet end, and an outlet end, wherein the device has at least one inlet port, and at least one outlet port, such that the device cannot be isolated from the circuit by direct reconnection of

the inlet end and outlet end, characterised by the steps of

i) breaking the pilot circuit to form an inlet end and an outlet end of the pilot circuit, and

ii) attaching a type A connector to the outlet end, and

iii) attaching to the inlet end a type B connector that is incompatible with the type A connector, and

iv) connecting an inlet port of the device to the type A connector on the outlet end of the pilot circuit, and

v) connecting an outlet port of the device to the type B connector on the inlet end of the pilot circuit.

According to another aspect of the present invention there is provided a kit for connecting a security device into a pilot circuit having an inlet end, and an outlet end, wherein the security device has at least one inlet port, and at least one outlet port, such that the security device cannot be isolated from the pilot circuit by direct reconnection of the inlet end and outlet end, the kit including, a security device, a type A connector configured to connect to the outlet end, and a type B connector that is incompatible with the type A connector, the type B connector being configured to connect to the inlet end. Throughout this specification hydraulic circuit should be understood to refer to a

network containing a liquid moving in a confined space under pressure. Similarly a pneumatic circuit should be understood to refer to a network containing a gas moving in a confined space under pressure.

Reference throughout this specification will be made to hydraulic circuits. However, those skilled in the art will appreciate that other circuits, such as pneumatic circuits, may also be used and that reference to hydraulic circuits only should in no way be seen as limiting.

Reference throughout this specification to an inlet end should be understood to mean an end of a hydraulic circuit into which fluid flows and to an outlet end to mean an end of a hydraulic circuit from which fluid flows.

Throughout this specification an inlet port should be understood to refer to an opening into which fluid may flow and an outlet port to an opening from which fluid may flow.

Throughout this specification connector should be understood to refer to an attachment to an open end of a hydraulic circuit configured so as to effect a connection.

Reference to a connection throughout this specification should be understood to refer to a link between two components of a hydraulic circuit such that liquid is confined to flow across the link under pressure. Two connectors are referred to as incompatible if they cannot be linked directly together to form a connection.

Hydraulic circuits form part of the operating system of a wide variety of machines, particularly those with operating systems involving mechanical movement of machine parts. Common examples include, without limitation, construction machines, front-end loaders, diggers, forklifts and tree harvesters.

In some embodiments the present invention is used in a hydraulic circuit of a machine and includes a switching mechanism. The switching mechanism may have a valve which directs fluid flow from an operational state, in which the machine may be operated in a normal manner, to a non-operational state in which the machine is immobilised.

In some embodiments the security device is installed into a hydraulic circuit of a construction machine.

Reference throughout this specification will be made to a security device in accordance with the present invention being installed in a construction machine. However, those skilled in the art will recognise that the security device could be installed in any hydraulically operated machine, and reference to construction machines only throughout this specification should in no way be seen as limiting.

Preferably the security device as described above is installed in a manner such that the device cannot be readily isolated from the hydraulic circuit.

The advantage provided by the current invention is that, following removal of the security device the circuit cannot be reconnected using the existing connectors. A typical hydraulic circuit consists of a closed circuit in which a number of devices are connected by pipes or flexible hoses.

The security device of the present invention may be installed in the pilot circuit.

A pilot circuit may contain one or more devices which are activated by the pressure exerted by the hydraulic liquid. Hydraulic liquid is transferred between devices through pipes or hoses. The individual devices, hoses and or pipes form the components of a pilot circuit.

In a preferred embodiment the hydraulic liquid is transferred by a hose.

The advantages of using hoses in application of the current invention are that connections are more readily formed and the hoses are sufficiently flexible to allow inclusion of additional devices, such as a security device.

Reference throughout this specification will be made to the transfer of liquid through a hose. However, those skilled in the art will recognise that other forms, such as pipes, may be used and reference to hoses only throughout this specification should in no way be seen as limiting. Connections between the components of the pilot circuit are effected by, coupling suitably configured connectors.

Connectors may be formed in a wide variety of sizes and shapes depending on the application. They may be formed in complementary pairs, so that for every first connector there is a second complementary connector which is configured to form a connection with the first connector.

If two connectors are not complementary then they are incompatible and no direct connection between them is possible.

Throughout this specification a connector will be denoted by an upper case letter of the alphabet, e.g. A. A complementary connector to A will be denoted by a prime, i.e. A'. A connection between two complementary connectors A and A' will be denoted by a colon, i.e., A:A'. A direct connection between two connectors A and B, is only possible if B is the same as A'. In cases where B is not the same as A', no direct connection is possible and A and B are said to be incompatible.

An adaptor may be used to form a connection between a pair of incompatible connectors. Throughout this specification an adaptor should be understood to refer to a connecting device having at least one inlet end and one outlet end, the inlet end configured to form a connection with a connector and the outlet end configured to form a connection with another connector, in situations where the connector attached to the inlet end is incompatible with the connector attached to the outlet end.

An adaptor may be formed by linking two incompatible connectors, C and D together by attaching C and D to opposite ends of a hose. Alternatively the adaptor may be formed as a single composite unit such that one end is configured as a C connector and the opposite end as a D connector. An adaptor will be denoted by a hyphen, i.e., C-D.

The simplest connection is formed by coupling a pair of complementary connectors to each other. More complex connections may be formed by linking a chain of connectors and adaptors together.

In a preferred embodiment the connectors are screw-connectors. Throughout this specification a screw-connector should be understood to refer to a connector configured to form a connection by means of a screw thread.

Screw-connectors are commonly used to connect hydraulic circuits. They provide the advantage of forming robust connections by coupling two appropriately configured screw-connectors together using a spanner. Reference throughout this specification will be made to screw-connectors. However, those skilled in the art will recognise that other types of connectors may be used and reference to screw-connectors only throughout this specification should in no way be seen as limiting.

A screw-connector may have a screw thread on an outer surface (commonly referred to as a male connector) or on an inner surface (commonly referred to as a female connector).

A screw thread may be either right handed or left handed depending on whether it is configured to turn clockwise or anticlockwise in order to form a connection.

Screw-connectors are also characterised by their size and thread type. Size is measured by the outer diameter of the screw section of the male connector and the inner diameter of the screw section of the female connector. Thread pitch is a measure of the separation of consecutive windings of the screw thread. Reference throughout this specification to different thread types should be understood to include differences in size, thread pitch and/or left and right handedness.

Screw connectors may also be classified in terms of the shape of the distal end of the male connector and corresponding inner end of the female connector. Screw-connectors are normally configured to comply with one of a range of internationally recognised standards for thread pitch and shape. Examples of these standards include, without limitation, British Standard Pipe (BSP), Society Automotive Engineers (SAE) and National Pipe Taper (NPT). Those skilled in the art would appreciate that there is a range of these standard screw types and reference to any particular standard in this specification should not in any way be seen as limiting to that standard.

A connection between two screw connectors can only be formed by screwing together two complementary screw-connectors.

Reference throughout this specification to complementary screw-connectors should be understood to refer to a male connector and a female connector of the same size and thread type. Hence for example a three quarter inch BSP male connector will be complementary to a three quarter inch BSP female connector. Similarly a ten millimetre SAE female connector will be complementary to a ten millimetre SAE male connector. Two screw-connectors are incompatible with each other if they are both male or both female, if they are of different sizes, or if they belong to different standard thread types. Right handed screw thread connectors are incompatible with left handed screw thread connectors.

In a preferred application of the present method a security device is connected into the pilot circuit through connections formed by two or more screw-connectors and adaptors to the inlet and outlet ports of the device.

In a preferred application the security device is connected to the inlet connector on the housing of a filter.

Throughout this specification a filter should be understood to refer to a device in a hydraulic circuit containing porous material for removing solid particles from the hydraulic fluid.

Reference throughout this specification will be made to connection of the security device to the connector on the housing of the filter. However, those familiar with the art will understand that this position is chosen merely as a convenient place to attach the security device, and that the method of connection applies equally to attachment of the security device to any component of the circuit.

Preferably the outlet end of the hose is disconnected from the input connector on the filter housing. A suitable connector, denoted type A, is used to form a connection between the input port on the filter and the outlet port on the security device. Similarly a type B connector is used to form a connection between the output end of the disconnected hose and the input port of the security device.

In a preferred embodiment the input port of the security device has a left handed thread.

Right handed screw threads are by far the most common form of screw thread used in connectors. Left handed screw threads are normally only used on connectors attached to parts that rotate in an anticlockwise direction (when viewed from the top of the connector). In this situation a right handed screw thread may be loosened by the rotation, whereas the rotation tends to tighten a left handed thread.

Use of a left handed thread to connect to a fixed security device would therefore not be expected, thus adding to the security aspect of the installation. Anyone intending to remove the device would expect a right handed thread, thus tightening a left handed connector when attempting to undo it.

Furthermore, for the reasons given above, left handed screw adaptors are very uncommon. It is therefore unlikely that anyone intending to remove the device would have a left handed adaptor to use in reconnection of the circuit.

Both the type A connector and the type B connector may be formed by a sequence of individual connectors and adaptors as required.

In a preferred embodiment the type A connector is incompatible with the type B connector, so that isolation from the circuit by reconnection of the inlet end of the hose to the outlet port of the filter is not possible without introducing additional connectors and or adaptors.

The number of combinations of connectors and adaptors that may be used in connecting the device into the circuit is very large. This provides the considerable advantage of dramatically increasing the difficulty of circumventing the security device as it is highly unlikely that the adaptor required to reform the connection will be available on site.

According to another aspect of the present invention there is provided a machine having a device installed using any of the methods substantially as described above. The security device as described above provides considerable advantages over the prior art. It can be retrofitted into any hydraulic circuit. Therefore it may be used to render inoperable any hydraulically operated machine by diverting the flow from the normal operating circuit.

Additional advantages arise from the security features provided by the current invention in that access to the switching mechanism is restricted to a key and that the device may be connected into the circuit in a manner which prevents reconnection of the circuit following unauthorised disconnection of the security device.

BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a schematic view of a pilot circuit including a security device; and Figure 2 shows a cross section view of a security device; and

Figure 3 shows a plan view of a security device; and

Figure 4 shows a flowchart of the method of connection to the security

device; and

Figure 5 shows a schematic view of connections to a security device; and Figure 6 shows a typical connection in a hydraulic circuit; and

Figure 7 shows a schematic view of the components of the connections with the security device in place; and

BEST MODES FOR CARRYING OUT THE INVENTION

A schematic of a security device installed in a pilot circuit of a hydraulically operated machine is shown in Figure 1.

A security device, generally indicated by (1 ) is connected to a pilot pump (16), a filter (17) and a tank (18). The filter (17) is connected to a pilot valve (not shown) which is connnected to a main control valve (not shown) which directs pressure to the main hydraulic circuit of the machine.

The security device (1) includes a switching mechanism in the form of a valve (19) which diverts the hydraulic flow between two modes of operation of the machine. In a normal operating mode, the valve (19) is set such that hydraulic fluid is pumped from the pilot pump (16) through the security device (1) to the filter (17) and on to the pilot valve (not shown).

In a non-operational mode, the valve (19) is set to divert flow of hydraulic fluid from the pilot pump (16) into a tank (18). The circuit of the non-operational mode is normally completed by a connection (not shown) between the tank (18) and the pilot pump (16).

When the security device (1 ) is set to the non-operational mode no pressure is delivered to the pilot valve and consequently not to the main hydraulic circuit. It is therefore not possible to operate the machine in the non-operational mode. Figure 2 shows a cross section view of part of a security device (1) having a housing (2) in which a cavity (3) has been formed. The cavity (3) contains a head (4), being the distal end of a connecting rod (5), such that the head (4) is recessed into the cavity (3) at a depth such that access to the head (4) requires application of a suitably configured key which engages with the sides of the head. Figure 3 shows a plan view of part of a security device (1) having a housing (2). A cavity (3) has been formed in the housing to provide access to a head (4). The

dimensions of the cavity (3) and of the head (4) are such that the sides of the head (4) are close to the sides of the cavity (3).

The shapes of the head and corresponding key are formed by a broaching machine. The broaching technique uses a vibrating cutting tool that can be controlled so as to form a substantially straight edge by shaving small amounts from an initially circular hole.

In this way the profile (5) formed on the head (4) with which the key engages is so close to the outer edge of the head (4) that on visual inspection from outside the housing (2) (down the cavity (3)) the head (4) appears to be cylindrical. The spacing between the edge (6) of the cavity (3) and the sides of the head (4) is chosen to limit access to the head (4) other than through use of a key which engages with the profile of the edge (5) of the head (4). Using the broaching technique to form the profile of the edge (5) of the head and the corresponding key, the spacing between the sides of the cavity (3) and the sides of the head (4) can be limited to around 2mm.

The profile of the edge (5) of the head (4) is limited only by the requirement that the edge remain in close proximity to the edge (6) of the cavity (3).

The profile of the edge (5) of the head (4), and of the corresponding key, may be varied for each installation or application of the invention. This has the advantage that different keys may be required to activate security devices fitted to different machines. This reduces the probability of unauthorised access being gained to a security device fitted to one machine through use of a key for a security device fitted to a different machine.

Figure 4 shows the steps involved in the method of connecting a device into a break in a hydraulic circuit, such that the device cannot be isolated through direct recombination of the hoses.

Figure 5 shows an exploded view of the components of a typical configuration and application of the method.

In step i), a device (1) is installed in a break in the hydraulic circuit between an outlet end (8) and an inlet end (9) of the circuit.

In step ii) a connector (10) is attached to the outlet end (8) of the hydraulic circuit. In step iii) a connector (11) is attached to the inlet end (9) of the circuit, such that

connector (11) is incompatible with connector (10).

In step iv) a connection is formed between the connector (10) and the inlet port (12) of the device.

In step v) a connection is formed between the connector (11) and the outlet port (13) of the device (1).

In practice a number of the connectors are predetermined by the manufacture of the devices and hoses to be connected. For example, the connectors formed as inlet and outlet ports on a device will normally be set during manufacture of the device. The inlet and outlet ports are typically formed as female screw connectors as these are readily machined into the housing of the device.

In most applications involving current hydraulically operated machines the connections are formed by screw-connectors.

Figure 6 shows a representation of a typical initial situation prior to connection of the security device. The outlet port (8) on the filter housing (14) will be configured as a female screw connector, A. A complementary male screw-connector, A' will be screwed into the female to form a connection A:A\ The inlet end (9) of the hose (15) will be fitted with a female screw-connector, A, so that the complete connection of the filter housing (14) to the hose (15), prior to attaching the security device, is denoted A:A':A. Other combinations, making use of adaptors, are possible but unlikely in a standard machine as manufactured, due to the unnecessary increased complexity. However, the method of connection as outlined below may be applied whatever the initial state of the connection.

Figure 7 shows a representation of a typical installation of a security device (1) following the current method. The inlet port and outlet port of the device are denoted as connectors B and C respectively.

In the step i) of the current method the initial connection as shown in Figure 6 is broken by unscrewing the connection between the filter and the hose. The connector A is then removed from the inlet end (9) of the hose (15) and discarded. This is a necessary step to ensure that the initial connection cannot be reformed.

In step ii) an adaptor, A'-B' is attached to the A connector on the filter housing (14) forming a type A connector denoted A:A'-B'.

In step iii) a new connector D is attached to the inlet end (9) of the hose (15). An adaptor, C-D', is attached to D to form a type B connector, denoted C'-D':D.

In step iv) the inlet port of the security device is connected to the type A connector, forming a connection between the filter and the device denoted as A:A'-B':B In step v) the outlet port of the security device is connected to the type B connector, forming a connection between the device and the hose denoted as C:C'-D':D.

The purpose of this method is to ensure that the circuit cannot be reconnected following unauthorised disconnection of the security device. A number of conditions must be met to ensure that the hose cannot be directly reconnected to the filter housing using the connectors and adaptors available in the type A and type B connections after the security device has been disconnected from the circuit.

In order to prevent reconnection of the hose to the filter following disconnection of the security device (1) it is necessary that B' and C are incompatible (as otherwise a connection could be formed by coupling B' to C). This is the same as requiring B and C to be incompatible. This is readily achieved by the normal situation in which the inlet port and the outlet port of the security device are both female. Otherwise they would need to be of different sizes or thread types. Each of the two adaptors may also be disconnected in order to form a new connection.

If A'-B' is removed then it is necessary that A (on the filter housing (14)) and C (on the end of the type B connector) are incompatible. As C is compatible with C (the connector on the outlet port of the security device), this equates to the condition that C must be different from A. As in most instances both A and C will both be female connectors, this requires that C is either a different size or thread type from A.

If C-D' is removed then it is necessary that D (on the inlet end (9) of the hose (15)) and B' (on the end of the type A connector) are incompatible. As B' is compatible with B (the connector on the inlet port of the security device), this equates to the condition that D must be different from B. As B is normally a female connector this condition is met if D is a male connector. Alternatively, they need to be of different sizes and or thread types.

If both adaptors are removed then it is necessary that A and D are incompatible. This is achieved if both are female or both male adaptors, or if they differ in size or thread type.

In practice the method may be applied by first choosing a security device configured such that the inlet port connector (B) and outlet port connector (C) are the same and are different from the outlet on the filter housing (A). Assuming, as is the usual situation, that A, B and C are all female connectors, this requires that B and C are of a different size and/or thread type to A.

The connector to the inlet end of the hose (D) may then be chosen from any connector which is incompatible with A and different from B and C.

As the number of screw-connectors is very large there are numerous ways in which D may be selected. This provides the considerable advantage that unauthorised removal of the security device and reconnection of the circuit is not possible without access to an extensive range of adaptors. Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the appended claims.