There are various types of known fluid leak detection systems. Generally these include the use of water meters to monitor the flow rate of the water at one or more locations in the water supply. The flow rates at different locations are compared over a period of time and a decision is made based on this information whether or not a leak is present in the system. The flow meters used in this type of system emit pulses at a rate indicative of the fluid flow rate. Systems of this kind require a relatively complex combination of flow meters, timers and processing software to evaluate the information. If the leak is significant a substantial amount of water can be lost (and therefore significant damage can be caused) in the timed comparison and the evaluation period before any alan signal is activated.

It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.

According to the present invention there is provided fluid leak detection apparatus for a fluid supply system comprising a fluid supply conduit and at least one fluid outlet conduit, the apparatus comprising a fluid supply shut-off valve connected in a fluid supply conduit, a first flow switch in the fluid supply conduit and which is actuated when the fluid flow exceeds a first pre-detennined value, a second fluid flow switch in said outlet conduit and which is actuated when the fluid flow exceeds a second pre-determined value, and control means that operates to close the shut-off valve when only the first fluid flow switch is actuated.

Preferably the control means incorporates a timer that provides a delay of a predetermined period between the actuation of one of said first and second flow switches and operation of the shut-off valve to check that the flow switch remains in the actuated condition for that predetermined period before operating the shut-off valve. This check ensures that the shut-oft valve is not closed flow a predetermined period of time, thereby allowing for errors caused by transient conditions.

An audio and/or visual alarm may be provided to indicate when a shut-off valve has been operated.

Preferably there is a plurality of outlet conduits each having a second fluid flow switch.

Preferably there is both a hot and cold supply conduit each having a shut-off valve and a first fluid flow switch.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a typical domestic water supply system fitted with the leak detector of the present invention; and Figure 2 is a block diagram of a control unit of the present invention showing input and output control signal paths.

Referring now to the drawings. figure 1 shows a typical domestic water supply layout comprising a main cold water supply conduit I with a plurality of branch conduits 2 that connect to household appliances such as bathroom and kitchen taps 3.

The main cold supply conduit 1 feeds into a hot water tank 4 the output of which is a main hot water supply conduit 5 with branch conduits 6 corresponding to those in the cold supply conduit 1. The main cold water supply conduit 1 additionally has a branch conduit to a WC which has no hot water supply.

The beginning of each main supply conduit 1,5 is fitted with a normally closed shut-off valve 7,8 and an adjacent flow switch 9,10. Each shut-off valve 7,8 is actuable via a microswitch in response to an electrical signal Ci, C2 from a control unit (described below) to close the respective supply conduit 1,5. The microswitch is activated to cut off the power supply to the shut-off valve thereby causing it to revert to its normally closed condition. Closure of each valve 7.8 may be effected by, for example, solenoid or motor operation. Each flow switch 9,10 comprises, for example, a reed switch plunger mechanism with an electrical output signal Sl, S2. The flow switch status as indicated by the output signal Sl, S2 2 toggles when the volumetric water flow rate in the conduit exceeds or falls below a predetermined value (for example 1.25 litres per minute). A flow switch of this type is commercially available from RS components under stock nos. 257-076 and 257-082.

Each branch conduit 2,6 is also fitted with a flow switch 11-17 at a location adjacent the appliance. These flow switches 11-17 are designed so that the switch status signal S3 to S9 toggles (between on and off) when the volumetric flow rate in the respective branch conduit 2,6 6 exceeds or falls below a predetermined value (for example 0.5 litres per minute). A flow switch 18 is also connected in the pipeline immediately prior to the hot water tank 4. This switch emits a signal Sl() when it is triggered by a predetermined flow rate.

Any electrical "on" signals Sl to Sl0 generated by the flow switches 9-1 8 are transmitted to a control unit (see figure 2) that monitors the status of the signals Sl to Slo and sends control signals Cl, C2 to the shut-off valves 7,8 to cause them to open or close as necessary. The control unit incorporates a timer (not shown).

With the shut-off valves 7,8 both open, water flows in the normal operative state along the main cold water supply conduit 1 to the hot water tank 4. If cold water is demanded by any appliance (e.g. by flushing the WC or turning on the tap in the kitchen) cold water is supplied along the respective branch pipe 2. Similarly hot water flows from the hot water tank 4 along the main hot water conduit 5 and into the branch pipes 6 associated with any appliances which are demanding hot water. In this normal operative state the flow rates of water in the various conduits will exceed the threshold of the flow switches 9 to 18 and any active signals Sl to Sl() will be transmitted to the control unit, the output signals C,, C2 of which will be inactive.

In the event that no appliances are in use the flow switches 9 to 1 8 transmit no signals to the control unit thereby representing their passive state and again the outputs C1, C2 of the control unit will both be inactive. However, in the event of a leak in either the hot or cold water supply and when appliances connected to that supply are not in use, only one or both of the flow switches 9 and 10 in the main supply conduit 1 or 5 will be active. When the signals SX, S2 received by the control unit represent this set of circumstances the control unit will transmit a control signal Cl or C2 to activate the relevant shut-off valve 7,8. The timer in the control unit will only permit transmission of this control signal if the condition is maintained for a predetermined period to allow for er r ors caused by transient conditions. For example, when an empty system is being charged with water it is necessary to avoid closure of the shut-off valves. The length of predetermined period can be set by the user.

When one or both valves have been shut down an alarm (visual, audible or both) will be activated.

Provision may be made for manual override of the system if one or both of the shut-off valves are activated. When a shut-off valve is closed it remains closed until it is manually opened. Since each shut-oft. valve is normally closed it is fail safe so in the event of power loss each valve will be closed.

The apparatus conveniently enables isolation of hot and cold water supplies separately.

In an alternative embodiment (not shown) a flow switch is provided in a supply pipe that is external to the domestic premises and interconnects the internal conduits to the water main. The switch may be positioned for example, adjacent an external stop tap. This arrangement permits the detection of leaks in the external water supply by making use of the same techniques described above. In normal use the external flow switch will generate a signal that is indicative of flowing water and this is compared to the signal S1 generated by the inlet flow switch 9. Provided both signals are active there is no leak. However should the external flow switch transmit a signal and the inlet flow switch 9 does not. there must be a leak in the external pipework. This condition is detected by the control unit and a visual and/or audible alarm is activated. The user can then inform the water switch to that in the inlet pipe (flow switch 9) may be provided if a lower rate of flow detection supply company. If necessary an additional flow is required.

It will be appreciated that the above described apparatus for leak detection may be applied to other water supply apparatus such as a central heating systems or an industrial water supply.