The present invention relates generally to security devices serving as immobilisers.

In a first aspect, the present invention relates to the security of plant machinery, especially plant machinery including hydraulically-operated devices.

Items of plant machinery such as diggers, earth movers, dumper trucks and forklift trucks, which commonly include hydraulically-operated digging and lifting devices, are often left at night on site in an area which can be quite easily accessed by the public.

As a result, the theft and misuse of unattended plant machinery is a widespread occurrence.

It is an object of the first aspect of the present invention to provide enhanced security for plant machinery.

With this in mind, in accordance with the invention there is provided an hydraulic circuit of an item of plant machinery comprising: at least one hydraulically-operated device; a fluid tank; a pump for supplying fluid, at high pressure, from the tank to the at least one hydraulically-operated device; a lockable valve, the circuit providing, when the valve is in its locked condition, a low pressure return passage to the tank, through the valve, for the high pressure fluid supplied from the pump, whereby insufficient fluid pressure

is supplied to the least one hydraulically-operated device for it to operate, the valve blocking the return passage when in its unlocked condition.

The invention also provides: a valve comprising: a housing having an inlet and outlet port; a lock; a valve member coupled to the lock; and a valve seat, the valve member being moveable from a first position at which it rests upon the valve seat and thereby blocks the path from the inlet to the outlet port, when the lock is in its unlocked condition, to a second position at which the valve member is displaced from the valve seat in a direction generally towards the inlet port and thereby provides a passage from the inlet port to the outlet port, when the lock is in its locked condition.

Preferably, the valve member includes a spring which is operable to bias the valve member into its first position.

Preferably, the lock is movably mounted in the housing and moves in unison with the valve member. The movement of the valve member and lock may be linear and can be co-linear.

The valve in accordance with the first aspect of the invention is the preferred valve for use with the hydraulic circuit as previously defined.

Using the valve, as previously described, a determined criminal with a good knowledge of hydraulics could overcome and defeat the system by disconnecting the valve from the circuit and fitting a blanking

plug.

For this reason, the present invention also provides a device for protecting the coupling between a fluid conduit and an element of an hydraulic circuit, the element including a body, a port and a first adapter mountable to the port, the fluid conduit having a second adapter, which is disposed at one end thereof, and can be screwed to the first adapter to form the coupling, the device comprising a collar having an internal flange at one end thereof, the collar being adapted to be arranged, in use, such that it surrounds the coupling and the internal flange is retained between the body of the element and the first adapter, the dimensions of the collar being such that there exists a small gap between the inside surface of the collar and the outside surface of the first adapter.

In order to attach and detach the first and second adapters a spanner in accordance with the invention is provided. The spanner comprises a operating portion and a sleeve of generally C-shaped cross-section projecting from the operating portion, the sleeve being adapted to fit in the small gap between the inside surface of the collar and the outside surface of the second adapter, and engage the outside surface of the second adapter.

In a second aspect, the present invention relates to an hydraulic valve for use in an hydraulic braking circuit of a vehicle as an immobiliser.

In accordance with a second aspect, the present invention provides a valve for a hydraulic braking circuit of a vehicle comprising: a housing including a first port for connection to the master cylinder of a braking circuit; a second port for connection to at least one

wheel cylinder of the braking circuit; and a first major passage connecting the first and second ports; a first valve means disposed in the first major passage; a lock, the first valve means being operable when the lock is locked to block only liquid flowing along the first major passage from the second port to the first port, and when the lock is unlocked to permit bidirectional liquid flow along the first major passage, the valve further comprising; a first bleed-back means including a first minor passage which has both its end portions in communication with the first major passage, the first minor passage defining a path along which liquid can seep from the second port to the first port when the lock is locked.

In a third aspect, the present invention relates to a three port valve and to a parking brake system for a vehicle, which includes the three port valve.

Lorries are usually equipped with two independent braking systems: an hydraulic foot brake system for braking the lorry when it is in motion; and a pneumatic, parking brake system, activated by a handbrake, which once the lorry has stopped, maintains the lorry in a stationary state.

A known parking brake system for a lorry is shown in schematic form in Figure 13.

The system comprises a compressor (not shown) which supplies compressed air via conduit 410 to a reservoir 412. The reservoir 412 is connected via a conduit 414 to a handbrake unit 416. The handbrake unit 416 includes a control member 418 actuatable by an operator into ON and OFF positions; an outlet 420; and a vent 422. The outlet 420 of the handbrake unit 416 is connected via conduit 424 to an inlet of a parking

brake (not shown). The compressor and the handbrake unit together comprise a handbrake means.

The parking brake is a conventional pneumatic brake (and hence is not shown) in which a braking cylinder having a piston mounted therein is positioned at the inlet of the parking brake. The piston is coupled to braking blocks which can be brought into braking contact with the lorry wheels. The piston is biased by the applied pressure of a spring into a position at which the braking blocks are in braking contact with the lorry wheels. On application of air pressure to the inlet beyond a given super- atmospheric level, the biasing action of the spring can be overcome and the piston moved such that the braking blocks do not contact the lorry wheels.

In operation, when the control member 418 is in an OFF position, the handbrake unit 416 provides an open communication path 415 between the conduits 414, 424. This permits the compressed air from the compressor to flow directly to the inlet of the parking brake and, thereby, build-up the air pressure at the inlet of the park brake to a level at which the biasing of its spring is overcome and the brake blocks are released from engagement with the lorry wheels. On placing the control member 418 into an ON position, the handbrake unit 416 is operable to obstruct the communication path 415 and so isolate die conduits 414, 424 from one another, and then to vent the compressed air in conduit 424 to atmosphere through vent 422. This brings the air pressure in the conduit 424, and hence at the inlet of the parking brake, down to atmospheric pressure and, thus, causes the parking brake to effect braking, as previously explained.

It is an object of the third aspect of the present invention to modify the parking brake system shown in Figure 13 so as to provide a system of

greater security.

In accordance with a third aspect of the present invention, there is provided a parking brake system for a vehicle comprising: a handbrake means, which includes a source of compressed air; an oudet to which the compressed air is supplied; and a control member actuatable by an operator, the handbrake means being operable, when the control member is in an ON position, to isolate the source of compressed air from the outlet and vent the outlet to atmosphere and, when the control member is in an OFF position, to provide a flow path between the source of compressed air and the outlet; a parking brake having an inlet to which can be supplied compressed air from the outlet of the handbrake means, the parking brake being operable to effect braking when the air pressure at its inlet is below a given super- atmospheric level;

the system further comprising a lockable valve which is operable in a locked state to disable the parking brake.

Exemplary aspects of the invention are hereinafter described with reference to the accompanying drawings, in which:

Figure 1 shows a cross-sectional view of a valve in accordance with the first aspect of the present invention;

Figure 2 shows a cross-sectional view of an hydraulic circuit in accordance with the first aspect of the present invention incorporating the valve of Figure 1 in its unlocked or drive condition;

Figure 3 shows the hydraulic circuit of Figure 2 when the valve is in its locked or disabling condition;

Figure 4 shows a view in cross-section of one embodiment of a coupling protection device in accordance with the first aspect of the present invention;

Figure 5 shows a perspective view of the spanner forming part of Figure 4;

Figure 6 shows a view in cross-section of another embodiment of a coupling protection device in accordance with the first aspect of the present invention;

Figure 7 shows a valve in accordance with a second aspect of the present invention in cross-section in its unlocked state;

Figure 8 shows the valve of Figure 7 in its locked state;

Figure 9 shows a valve in accordance with a second aspect of the present invention, in use, in a vehicle braking system;

Figure 10 shows a valve of the third aspect of the present invention in its drive state;

Figure 11 shows a valve in Figure 10 in its locked state; and

Figure 12 shows a parking brake system in accordance with the third aspect of the present invention incorporating the valve of Figures 10 and 11.

Referring to Figure 1, a valve in accordance with the first aspect of the present invention is generally designated by the reference numeral 10.

The valve 10 includes a housing comprising a generally cylindrical body portion 12 having its longitudinal axis indicated by the dotted line A- A ¹ ; an end cap 13 disposed at a first end of the body portion 12; and a mouth portion 21 at the second end of the body portion 12. The end cap 13 is secured to the body portion 12 and defines a first port 14. An O- ring 23 provides a seal between the body portion 12 and the end cap 13. An outlet port 16 is formed in the side wall of the body portion 12.

The inlet and outlet ports communicate with one another via a passage which comprises two chambers, an outlet chamber 17 adjacent the outlet port 16 and a wider inlet chamber 15 adjacent the inlet port 14. The wall of the outlet chamber 17 which boarders on the inlet chamber 15 forms a valve seat 24. Each port 14, 16 includes threaded walls 19 for receiving a threaded male portion of a coupling.

The mouth portion 21 receives and provides for the axial movement of a barrel lock 25 along the axis A-A ¹ . When the lock 25 is in its locked condition as is shown in Figure 1 , a bar 27 projects from the barrel of the lock 25 and engages a recess 22 of the mouth portion 21. The end of the lock is coupled to a valve member 30 by means of a guide pin 29. The inlet chamber 17 is sealed from the mouth portion 21 by an 0-ring 34. The valve member 30 includes a spigot portion 31 which is attached to a spring 32. The spring 32 is operable to bias the valve member 30 towards the mouth portion 21 in the direction indicated by the arrow B.

It will be appreciated that when the valve 10 is in its locked

condition as illustrated in Figure 1, fluid entering the inlet port 14 is free to pass through the inlet and outlet chambers 15,17, past the valve member 30 and then to the outlet port 16.

When the valve 10 is put into its unlocked condition, the bar 27 of the lock 25 is retracted and the biasing action of the spring 32 comes into play, whereby the valve member 30 and the lock 25 move in unison along the axis A-A ¹ until the spigot portion 31 engages the valve seat 24. The valve 10 is shown in this condition in Figure 3. It will be appreciated that the flow from the inlet portion 14 to the outlet port 16 is prevented by the engagement of 0-rings 36 in the spigot portion 31 with the valve seat 24.

Figure 2 and 3 show the valve of Figure 1, in use, in an hydraulic circuit of an item of plant machinery, for example, a digger.

Referring to Figure 2 and 3, the hydraulic circuit comprises an oil tank 50 form which a pump 55 can draw oil and supply it at high pressure to hydraulically operated devices 100 in the circuit. For the sake of diagrammatic simplicity, these devices have not been illustrated, but might include, for example, the front and back buckets and the stabilizing legs of the digger.

In accordance with the invention, the hydraulic circuit also comprises a T-junction 60 at the outlet of the pump 55. The T-junction 60 provides a flow path from the pump 55 to the hydraulically-operated devices 100 (and then back to the tank 50) and also a flow path from the pump 55 straight back to the tank 50 via the valve 10 of Figure 1.

In use, when the valve 10 is in its unlocked or drive condition as shown in Figure 2 the valve 10 presents a closed circuit to the fluid

flowing to the valve 10 (see the arrow R), whereby the hydraulically- operated devices 100 are able to function normally. It will be noted that the higher the pressure in the circuit the more tightly the valve member 30 is urged against the valve seat 24.

When the valve 10 is put into its locked or disabling condition as shown in Figure 3, the valve 10 offers a low pressure return passage to the output of the pump (see the arrow R), whereby insufficient fluid pressure (see arrow C) is supplied to the hydraulically-operated devices 100 for them to operate so the hydraulic circuit is effectively disabled.

If, for example, prior to leaving a digger the operator dropped the front and back buckets, digging them into the earth, jacked the stabilizing legs down hard and then locked the plant lock into the disabled position as in Figure 3, thereby making it impossible to raise the hydraulic operated buckets and legs, it would be difficult for an unauthorised person to move the digger.

Using the lockable valve 10 as previously described a determined criminal with a good knowledge of hydraulics could overcome and defeat the system by disconnecting one of the couplings marked V in Figure 2 and fitting a blanking plug. For this reason, the present invention also provides devices for securing those couplings; the device, designated 101, is featured in Figures 4 to 6. In Figure 4 the device 101 is shown protecting the coupling to the inlet portion 14 of the valve 10.

It will be appreciated that the device 101 can be secured to the ports of any element of an hydraulic circuit, for example, the T-junction 60.

In this example, the coupling comprises a first adapter 110 having a nut 110a and two threaded male portions, one of which can engage the threaded walls 19 of the inlet port 16 and die other of which can engage the internal threads (not shown) of a second adapter 120, the second adapter also including a nut 120a and being connected to the end of a hose 95.

The device 101 itself comprises a cylindrical collar 102 having an internal flange 103 at one end thereof. The collar 102 is preferably made from case-hardened steel.

As will become apparent, hereinafter, a special spanner 130 is required to attach and detach the device 101. It comprises a operating portion 132 and a sleeve 134 of generally C-shaped cross-section projecting from the handle portion 132. The internal cross-section of the sleeve 134 is selected to match the external cross-section of the nuts 110a, 120a of the coupling. The operating portion 132 can include a handle portion.

In order to attached the hose 95 to d e inlet port 14, the first adapter 110 is positioned inside the collar 102 such that one of its threaded male portions projects through the aperture defined by die internal flange 103. The first adapter is then screwed into the first portion 14 using the spanner 130, the sleeve 134 of which, it will be noted, fits in a small gap between the inside surface of the collar 102 and the outside surface of the first adapter 110.

The sleeve 134 need not snugly fit into the gap between the collar

102 and the first adapter 110, although this arrangement is preferred. However, it is preferred that the gap is relatively small as this prevents the

use of other more conventional spanners.

Next the second adapter 120 is screwed onto die first adapter 110 again using the spanner 130. It will be appreciated tiiat as the second adapter 120 is screwed onto the first adapter 110, the sleeve 134 of d e spanner 130 will extend only partially into the collar 102 in order that die nut 120a can be rotated relative to the nut 110a.

Once the adaptors are connected as shown in Figure 4, die spanner 130 is removed.

The use of a case-hardened steel makes the collar 102 very difficult to cut away from the coupling 110, 120.

Once the spanner 130 is removed, die would-be tiiief is presented witii a coupling which is completely inaccessible to any conventional spanner.

Preferably, the adapter 110 is not screwed tight against the valve 10, but is slightly spaced therefrom, so that collar 102 can rotate relative to the coupling 110, 120. This makes tampering with the collar 102 even more difficult.

In another embodiment featured in Figure 6, die security device 101 also includes an insert 140 which is interposed between the first adapter 110 and the internal flange 103. The insert 140 comprises an annular ring 142 having an annular flange 144 upstanding dierefrom. The insert 140 and particularly the flange 144 is dimensioned such that when d e insert 140 contacts the flange 103 and die adaptor 110 as shown in Figure 6, die flange 144 projects through the aperture defined by the flange 103, and

can contact the valve 10. Thus, it may seem tiiat as the adaptor 110 is screwed into the inlet port 14, it is only the insert 140 which is held tightly between the nut 110a and the valve 10, the collar 102 being free to rotate in a gap 146 created by the flange 144.

An advantage of d e Figure 6 arrangement over that shown in Figure 4 is tiiat the operator is not required to create intentionally the gap between the collar 102 and the valve 10 (ie. by deciding not to screw die adapter 110 tight against d e valve 10), but is merely required to fit the security device 101 to the coupling 110, 120, an appropriate size gap arising from the structure of the security device 101 itself.

In odier embodiments, die first adapter 110 need not be screwable to die circuit element, but may be attached thereto in another way. In such an instance, it will be appreciated tiiat the sleeve 134 would not need to be substantially as long as die collar 102 and there would not necessarily be a small gap between the first adapter 110 and the collar 102.

An item of plant, such as a digger, fitted with both the valve 10 and die collar 102 would be very difficult to steal.

The preferred embodiments of die second aspect of the invention which are hereinafter described are either two or four port valves.

A two port valve of the present invention is generally denoted 210 and featured in Figures 7 and 8. The valve comprises a cylindrical housing 212 having first and second ports 214, 216 which are connected by a first major passage 218. In a central portion 219 of the first major passage 218, the housing is shaped such that the first major passage is

generally cylindrical shaped. The valve 210 further comprises a cylindrical body portion 220 which is mounted for rotation in die central portion 219 of the first major passage 218. The body portion 220 includes first and second intersecting channels 222, 224 and can be rotated by die locking or unlocking of a key-operated lock, which is not illustrated but forms part of the valve 210, such that eitiier, as in Figure 7, the first channel 222 is co-linear with the first major passage 218 or, as in Figure 8, the second channel 224 is co-linear with d e first major passage 218.

Within the second channel 224, a first valve means in the form of a one-way check valve comprising a spring 228 and associated ball 230. A seat 226 is provided to co-operate with die ball 230 as shown in Figure 8.

The valve 210 also includes a first bleed-back means 240. The bleed-back means includes a first minor passage 242 having both its end portions 242a, 242b in communication with the first major passage 218. The portion 242c of the passage intermediate the end portions 242a, 242b houses a bleed plug 244 having a conical nose 245. The bleed plug 244 is mounted for radial movement in the portion 242c of die passage 242 on screw threads 246. By adjusting die radial position of the plug 244 the extent of penetration of the nose 245 into die end portion 242a can be altered, whereby the amount of liquid which can seep between the nose 245 and the end portion 242a can be controlled.

The four port valve, mentioned earlier, effectively comprises two of die two port valves axially spaced from one another and housed in die same cylindrical housing 212. The housing 212 thus also includes tiiird and fourth ports; a second major passage connecting the third and fourth ports, the valve further comprising a second valve means disposed in d e

second major passage, the second valve means being operable when the lock is locked to block only liquid flowing along d e second major passage from the fourth port to the third port and when die lock is unlocked to permit bidirectional liquid flow along the second major passage, die valve further comprising a second bleed-back means including a second minor passage which has both its end portions in communication witii d e second major passage, the second minor passage defining a path along which liquid can seep from the forth port to die third port when the lock is locked. The first major and minor passages are isolated from the second major and minor passages using seals (not shown). In the four port valve, the single lock serves to rotate both the first and second body portions, each valve means being in its locked or unlocked position at the same time.

In order explain the operation of die second aspect of the present invention, Figure 9 shows a four port valve fitted into a conventional dual circuit braking system.

The system comprises a tandem master cylinder 300 including a pedal 302, each fluid output 304,306 being connected to two wheel cylinders 308,310,312,314 via an automatic braking system (ABS) 316, if one is fitted. The operation of such a system ( without the valve of the present invention ) is well known to the man skilled-in-the-art and so need not be described in detail here. However, by way of brief summary, when the pedal 302 is depressed, the two pistons within the master cylinder are actuated causing the fluid pressure in each fluid output

304,306 to increase, which pressurises the respective wheel cylinders

308,310,312,314 and activates the brakes. On releasing the pedal, the pressure in each fluid output 304,306 falls and the wheel cylinders are de- pressurised, thereby releasing the brakes.

The valve 210, in this case a four port valve, is fitted to the hydraulic braking system as shown in Figure 9, the first port being connected to the fluid outlet 304, the third port being connected to fluid outlet 310, the second port 216 being connected to die wheel cylinders 308,310 and the fourth port being connected to die wheel cylinders 312,314.

As the four port valve, as previously explained, effectively comprises two two port valves which operate in an identical manner, die operation of only one of die two port valves will be discussed in detail.

When the valve is unlocked, as shown in Figure 7, it will be appreciated that fluid from the master cylinder 300 can flow unhindered along the first major passage 218 and thus die operation of the wheel cylinders and hence the braking performance is completely normal.

When the lock is locked using the key, d e valve adopts die Figure 8 configuration. On depressing die pedal 302, it can be seen tiiat fluid from the master cylinder 300 passes along the first major passage 218 from the first port 214 to the second port 216, and thus through the first valve means 228,230, and pressurises die wheel cylinders 308,310 thereby locking the brakes. On releasing the pedal 302, fluid is blocked from passing along the first major passage 218 from die second port 216 to the first port 214 , keeping the wheel cylinders 308,310 pressurised and thus the brakes locked.

The only way fluid can then pass from the wheel cylinders 308, 310 back to the master cylinder 300 is through the first minor passage 242.

The fluid passes between the body portion 220 and the housing 212 into the end portion 242a of the first minor passage 242 and then seeps

between the very small gap between the bleed plug nose 245 and die end portion 242a, thence back to the master cylinder 300.

The time taken for sufficient fluid to seep past die bleed plug nose 245 in this manner to release the brakes is controlled by die position of the bleed plug 244. Screwing die plug inwardly reduces die fluid flow rate and increases the length of time die wheel cylinders remain underpressure and screwing die plug outwardly increases the flow rate, decreasing die time the wheel cylinders are pressurised.

From the foregoing, it will be appreciated tiiat once the valve is locked and die brake pedal 302 depressed, die brake cylinders remain pressurised for a time dependant on the setting of d e bleed plug 244. This means that for this pre-set time, die brakes are locked on thereby preventing any attempt to drive or tow the vehicle without first unlocking the valve 210. After this period, the brake cylinders are depressurised and die brakes released. However, while the valve remains locked, one actuation of the brakes will again lock on die brakes for the pre-set time period.

An advantage of the second aspect of the present invention is tiiat it immobilises a vehicle without continually applying the brakes, which is generally understood as being undesirable.

The pre-set time period can be, for example, one hour or as long as forty eight hours.

It is preferred that the pre-set time period is set and sealed in the manufacture's factory to prevent tampering.

In addition, the valve may incorporate an electrical device to cut the power to the starter circuit and set an LED flashing on the dashboard as a warning that the vehicle is immobilised when d e valve is locked. This has two functions (i) as an additional hurdle to be overcome by a would-be tiiief and (ii) as a means to prevent accidental attempts to drive away whilst the brakes are locked on by the autiiorised driver of d e vehicle.

The valve 210 may include additional electrical devices which allow it to be interfaced with any alarm and/or electrical immobiliser. Preferably, when the valve is set in either the locked or unlocked positions, the key is ejected and may not be left in the lock - in tins way preventing accidental switching.

Referring to Figure 10, the valve 450 of die third aspect of the present invention comprises a housing 455 having first, second, and tiiird ports 461, 462, 463, respectively, and an opening (not shown). A body portion 465 having first and second intersecting channels 471, 472 passing dierethrough is rotatably mounted in die housing 455.

A key operated lock (not shown) is disposed in d e opening and coupled to the body portion 465 such that on activation of the lock using a key, the body portion 465 is rotated within the housing 455 so that one of either the first or second channels 471, 472 provides a communication path between the first and second ports 461, 462, while the other channel is in communication with the tiiird port 463.

In Figure 10, the first channel 471 provides a communication patii between die first and second ports 461, 462 and the valve 450 can be said to be in its unlocked or drive state. Whereas in Figure 11, the second channel 472 provides a communication path between the first and second

ports 461, 462 and the valve can be said to be in its locked state.

The second channel 472 is provided witii a valve means comprising a spring 475 and a steel ball 476, which is biased to one end of the second channel 472.

Thus, it will be appreciated from Figures 10 and 11 that die end of die second channel 472 to which die steel ball 476 is biased can either be adjacent the second port 462 or the third port 463. Accordingly, in die housing 455, sealing means in the form of O-ring seals 477 have been provided at the second and third ports 472, 473. In this manner, when the ball 76 contact either of die O-ring seals 477, air is permitted to flow dirough the second channel 472 in only one direction.

The valve 450 has particular, but not exclusive, application to a parking brake system for a lorry. Such a system, in accordance witii d e present invention, is shown in Figure 12. This system is identical to die one described in the preamble of the application and shown in Figure 13 and (accordingly, similar parts have been given the same reference numeral), except that the valve 450, having an air horn 480 connected to its third port 463, is connected between the oudet of the handbrake unit 416 and the inlet of the parking brake. This connection is effected by means of conduits 424, 426, which connect the outlet of the handbrake unit 416 with the first port 561 of the valve 450, and die inlet of d e parking brake with the second port of the valve 450, respectively.

When the valve 450 is its unlocked or drive state, as depicted in

Figure 10, the operation of the system is identical to that described in relation to Figure 13, as the valve 450 merely presents an open communication path between the conduits 424, 426, as indicated by the

arrows A. In this state, the third port 473 is always sealed by the ball 476 which is biased into contact with the O-ring seal 477.

However, when the valve 450 is in its locked state, as depicted in Figure 11, the behaviour of die system is somewhat different, as the ball 476 blocks the passage of air from the first to second ports 461, 462, but permits the passage of air from the first to tiiird ports 461, 463 and from die second to tiiird ports 462, 463. Thus, when the control member 418 is in an OFF position, die compressed air from the compressor is vented to atmosphere as indicated by arrows B and die air in d e conduit 426 and die parking brake is vented to atmosphere as indicated by the arrows C, thereby locking die parking brakes on.

It will be understood, tiiat if an attempt is made to drive d e vehicle away with the valve 450 in the locked state, the air horn 480 is sounded continually by die compressed air from the compressor exiting the valve

450 via the third port 463, and the parking brakes remain locked on as no compressed air can pass die ball 76.

Furthermore, as an added measure of security, the system of the third aspect of die present invention can be provided with a further means which is responsive to the orientation of die body portion and operable to disable the ignition system of the vehicle when the valve 50 is in its locked state. This can be achieved using, for example, microswitches mounted on the body portion.