TECHNICAL FIELD OF THE INVENTION THIS INVENTION relates to a safety device and in particular but not limited to a safety device for use in conjunction with a pump circuit such as might be used to circulate an operating fluid in a swimming pool, spa bath, air conditioner or the like.

BACKGROUND ART

Pump circuits used in swimming pools and spa baths are used to recirculate water through a filter. An inlet is employed upstream of the pump which draws water into the pump circuit. Frequently, the inlet can be blocked, say with leaves or it has happened that small children can have limbs or other body parts drawn into the inlet. Where a blockage occurs, the pump can be damaged and/or in the case of a child, the child can be injured.

OUTLINE OF THE INVENTION It is an object of the present invention to alleviate at least to some degree the aforementioned problems associated with the prior art.

In one aspect, the present invention resides in a safety device including a power shut down unit for shutting down power to a pump in a pump circuit, the shut down unit having an electrical pressure sensor for sensing variations in pressure in the pump circuit and an electrical shut down circuit for shutting down power to the pump in the advent of the sensor detecting an adverse pressure condition in the pump circuit.

In another aspect, the invention resides in a pump circuit employing a safety device to shut down power to the pump in the advent of an adverse pressure condition existing in the pump circuit, the pump having an inlet and an outlet connected in the pump circuit so operating fluid can be pumped about the pump circuit, the safety device comprising an electrical pressure sensor for sensing pressure variations in the pump circuit and an electrical power shut down circuit for shutting down power to the pump

when an adverse pressure condition is sensed by the pressure sensor.

Preferably, the pressure sensor is located upstream of the pump. Advantageously, two pressure sensors are employed, one upstream and one downstream of the pump. It will also be appreciated that the sensor or other sensors can be located at other locations in the pump circuit.

A safety device preferably employs one or more time delay circuits to prevent inadvertent shut down of the power to the pump. Typically, a power-up time delay circuit is employed to account for initial pressure variations which might arise at initial power-up of the pump. Where a downstream pressure is employed, a pressure variation time delay circuit is preferably used to account for transit changes in pressure by say, an air bubble passing along the circuit.

Where the safety device is used in environments prone to temperature variation which might influence operation of the pressure sensor, it is preferable to employ a temperature compensation circuit to account for current variations brought about by changes in temperature.

The safety device is preferably configured for general purpose application inasfar as adjustability of sensed pressure bringing about shut down is concerned. To this end, the safety device typically includes high and low limit presettable circuits so that reference pressures can be preset for different applications.

BRIEF DESCRIPTION OF THE DRAWINGS Other advantages of the present invention will become apparent from a consideration of the following description of one preferred embodiment of the invention and wherein:- Figure 1 is a schematic diagram illustrating part of a pump circuit employing the teachings of the present invention; Figure 2 is a circuit diagram illustrating one preferred embodiment of a safety device according to the present invention;

Figures 3 and 4 are circuit diagrams illustrating a further embodiment of a safety device according to the invention; and

Figure 5 is a circuit diagram illustrating a further application of the present invention.

METHOD OF PERFORMANCE Referring to the drawings and initially to Figure 1, there is illustrated part of a pump circuit 10 employing a safety device 11 to shut down power to a pump 12 in the advent of adverse pressure conditions existing in the pump circuit. The pump circuit includes a pump inlet conduit 13 communicating with an inlet 14 of the pump 12 and an outlet conduit 15 communicating with an outlet 16 of the pump 12. In the illustrated embodiment, two pressure sensing lines are employed, namely a pump inlet pressure sensing line 17 and a pump outlet pressure sensing line 18.

The sensing lines 17 and 18 are coupled to a power shut down control unit 19 which is connected in series with the power supply to the pump along power lines 20 and 21. Thus, in the illustrated embodiment, pressure is sensed either upstream or downstream of the pump. As long as the pressure either upstream or downstream of the pump remains normal, power to the pump will be maintained by the control unit 19. Should the pressure sensed vary beyond predetermined limits, then power to the pump would be shut down by the control unit 19.

The control 19 employs a switching circuit and a typical circuit for a control unit 19 is given in Figure 2. Figure 2 illustrates a typical control unit 19 with a relay 22 in series with the active supply to the pump via plug 23 (see also Figure 1) and hence, power line 21. In Figure 2, relay 22 is shown in its normal operating position where power is being delivered to the pump. An SCR 24 fires when there is an adverse pressure condition in the pump circuit and as a consequence, the relay is operated to open the active circuit to shut down power to the pump. A reset switch 25 is used to commutate the SCR so power to the pump

can be restored after a shut down. In the illustrated embodiment, two pressure sensors 26 and 27 are employed to sense pressure along sensing lines 17 and 18 as depicted in Figure 1 with the sensor 26 sensing pressure upstream of the pump and the sensor 27 sensing pressure downstream of the pump. An RC circuit 28 creates a time delay of five seconds (in this case) to account for intermittent operation of the sensor 27 where say, a bubble passes through the pump. The other circuit elements employed in the control unit 19 include a 555 timer 29 which delivers clock pulses to a counter 30 so that an initial time delay after initial power up is brought into play, and after the initial time delay, the counter 30 delivers an enabling pulse to a solid state switch 31 so that the solid state switch 31 can respond to an open circuit condition at the pressure sensors 26 or 27 to gate the SCR 24 and thereby shut down power to the pump.

It will be appreciated that the present invention can be installed into an existing pump circuit for say, a swimming pool, spa bath or other similar water circulation systems and clearly has general application in situations where it may be desirable to monitor operation of a pump circuit and shut down power to the pump. This will be dealt with further below.

Referring to Figures 3 and 4, an embodiment of the present invention is illustrated which has greater flexibility in terms of application and adjustment when compared with the circuit of Figure 2. As can be seen, the output from the circuit of Figure 3 feeds the input of the circuit of Figure 4 which operates basically the same as the timer circuit portions of Figure 2 and this aspect need not be described further. The circuit of Figure 3 provides the sensor output and in this case employs dual solid state transducers, typically SENSYM SPX200DN transducers are used and these are illustrated at 31 and 32 with the transducer 31 being arranged to sense pressure variation above a

reference level and transducer 32 being arranged to sense vacuum, that is pressure variation below a reference level. Hence, transducer 31 would normally be located downstream while transducer 32 would normally be located upstream. Each transducer has a temperature compensation circuit 33 and an output amplifier 34 which feed respective comparator circuits 35 and 36. The vacuum reference level indicating an adverse condition is set at the potentiometer 37 while the comparator circuit 35 employs two branches which allow high and low pressure limits to be set for downstream sensing.

When an adverse condition is detected, a high output is generated at the output A and the circuit of Figure 4 is activated to shut down the pump and can be suitably configured to provide an indication of an adverse condition using an alarm or lighting indicators.

Figure 5 illustrates an application of the present invention to an outboard motor to bring about shut down of the water pump when a blockage occurs. An SPX200DN transducer is shown at 38 and three series connected diodes at 39 are used for temperature compensation. The transducer output is amplified at 40 and the output is inverted at 41 so that the switch at 42 will operate to trigger the time 43 when a blockage occurs thus lighting an LED 44 and sounding buzzer 45, the light and buzzer can be suitably positioned so that the driver of the boat initiates manual shut of the motor. Alternatively, an automatic shut down can be employed using the timer circuit of Figure 2 or Figure 3 suitably interfaced to the circuit of Figure 5.

It will be appreciated that the present invention has general application in both domestic and industrial environments and accordingly, whilst the above has been given by way of illustrative example of the present invention, there are many variations and modifications which will be apparent to those skilled in the art without

departing from the broad ambit and scope of the invention as set forth in the appended claims.