In the first case, particularly in the case of submersible pumps installed in wells, or in deep tanks, when the level of the liquid in the well or in the tank falls under the level at which the pump is installed, the pump can suffer damages, due in particular to overheating, if it continues to operate in the absence of the liquid. It is therefore important that devices are installed in the well, or the tank, for monitoring the level of the liquid and for stopping the pump, when the level of the fluid falls under a preestablished minimum level.

For this purpose, it is known to use of floating-type or resistive-type liquid level sensors, operatively connected to devices suitable to break off the electric supply of the motor that drives the pump, when the level of the liquid falls under a preestablished minimum level.

The floating sensors show the disadvantage that, due to rust, dirt, calcareous sediments or more else, they can be blocked and then be no more sensitive to the level variations of the fluid, becoming therefore absolutely ineffective. The resistive sensors are expensive and cause therefore an increase of the costs of pump safety systems.

The other above mentioned disadvantage, that is the idle working of the pump with outlet valve closed, may also result in a fast overheating of the pump motor, with consequent risks of damage and even explosion of the pump. Even though the pump can idle work without risks for its integrity, operation in such condition implies a waste of energy, with increase of the operating costs of the pump. In order to obviate this disadvantage, it is possible to provide the pump with a thermic probe, that detects the pump temperature, emitting a signal proportional thereto. This signal is sent to the control device, that provides to the stop the pump motor, when the temperature exceeds a preestablished value.

The use of the thermic probe implies a further heavier outlay, particularly in the case of submersible pumps installed in deep wells or tanks, because the thermic probe must be connected to the control device through long wires installed inside the well, or the tank.

It is a purpose of the present invention to provide a safety system for a hydraulic circuit that is reliable and inexpensive.

According to a first aspect of the present invention, there is provided a safety system for a hydraulic circuit in which a liquid is circulated by a pump, said system including a sensor for detecting the level of the liquid in a preestablished position of said hydraulic circuit and a control device operatively connected to said sensor and suitable to interact with the supply of a motor driving said pump, characterized in that, said sensor is an infrared ray sensor.

An infrared rays sensor is a robust and reliable sensor, with a low cost, that allows to improve the reliability and to reduce the cost of the safety systems for pumps.

In the case of a pump driven by an electric motor, the infrared ray sensor either can be powered by an electric circuit separate from the electric circuit that supplies the pump motor, or can be powered by the same electric circuit that supplies the pump motor.

In an advantageous version of the invention the sensor is directly installed on the pump and is powered through the connecting terminals of the electric motor that drives the pump.

That allows to simplify and make less expensive the installation of the control device.

In a further advantageous version of the present invention, a thermic sensor is integrated into the infrared ray sensor, suitable to detect a temperature representative of the temperature of the pump body, the motor driving the pump or the fluid inside the hydraulic circuit.

This allows to carry out, with a single device, whether the control of the level of the fluid in the hydraulic circuit in which the pump is installed, or the control of the operating temperature of the pump, or its motor, or the control of the temperature of the liquid in the hydraulic circuit, with saving of costs and constructive simplification of the control system.

In a further advantageous version of the present invention, the infrared ray sensor is powered intermittently, at preestablished intervals of time.

This allows, by suitably choosing the interval between two consecutive supply cycles and the duration of each sensor supply cycle, to effectively monitor the operation of the hydraulic circuit, minimizing the employment of the sensor, which makes possible to lengthen the life of the sensor significantly.

The invention could be better understood and carried out with reference to the following description and the enclosed drawings, that illustrate some ways for carrying out the invention, with merely indicative and not restrictive purpose, wherein: Figure 1 is a sketched section of a well, in which a pump and an infrared ray sensor according to the invention are inserted, in separate positions; Figure 2 is a sketched section as Figure 1, but with the infrared ray sensor mounted directly on the pump; Figure 3 is a schematic diagram of the control system: according to the invention, concerning a version in which the infrared ray sensor is powered independently of the pump.

Figure 4 is a schematic diagram as Figure 3, concerning a version of the invention in which the infrared ray sensor is powered by the same supply line that powers the pump.

In Figure 1, a well 1 is shown, inside which, near its bottom, a submersible electropump EP is inserted, powered from the outside of the well 1 by a supply line 2. Furthermore, inside the well 1, at a preestablished depth, under the level L of the liquid contained into the well, an infrared ray sensor S is inserted, powered by a second electric supply line 3, distinct from the electric supply line 2 of the electropump EP. The infrared ray sensor S (Figure 3) is d. c. powered by a feeder AL arranged outside the well, through a control device DC. In addition the feeder AL supplies a relay switch R connected to the supply circuit of the electropump EP. The relay switch can be either of normally-closed or normally- open type.

The sensor R includes an infrared ray emitter and an infrared ray receiver, for example a photo-transistor, enclosed in a case, for example of plastic material, that constitutes a separating means between the emitter, the receiver and the environment outside the sensor.

The infrared ray emitter is powered by the feeder AL, while the phototransistor is connected to the control device DC. The material that constitutes the case of the sensor S, has such properties that, when the sensor S is immersed in a liquid, for example water, in the well 1, a portion of the infrared radiation emitted by the infrared ray emitter passes through the case and scatters into the water, while the remaining portion of the infrared radiation is reflected by the case and is intercepted by the infrared ray receiver, that emits e signal, for example of electric type, that is transmitted to the control device DC. When, on the contrary, due to the lowering of the level of the liquid in the well 1, the sensor S lies above the level L of the liquid, there is a variation of the refraction index at the interface between the case and the outer environment, which causes almost the totality of the infrared radiation emitted by the emitter of infrared radiation to be reflected by the case and be intercepted by the infrared ray receiver. The increase of the amount of infrared radiation intercepted by the receiver produces an increase of the intensity of the signal generated by the receiver and transmitted to the control device DC.

This increase of the intensity of said signal activates the control device DC, suitably set, which, through the feeder AL, activates the relay switch R so as to open the supply circuit of the electropump, stopping it. When the water level in the well 1 rises again until the sensor S lies once again completely immersed in the water, the amount of infrared radiation reflected by the case decreases and, consequently, also the intensity of the signal decreases that the receiver of infrared radiation transmits to the control device DC, which, detecting the decrease of the signal intensity, causes, through the feeder AL, the relay switch R to be closed and reestablishes the power supplying of the electropump EP.

The Figure 4 shows a block diagram of a control system according to the invention, in which the sensor S is powered by the same supply line 2 that supplies the electropump EP. In this case, when, for example, the power line 2 of the electropump EP is a three-phase line, the feeder AL is connected to a single phase of the power line 2, for example at the terminal box of the pump.

This solution is particularly advantageous if the electropump is arranged in deep wells or tanks, because it is possible to eliminate the long wires for the supply of the sensor, with saving of costs and simplification of the installation of the control system. In this case, also the control device DC and the relay switch R are installed directly on the pump, together with the feeder AL and the sensor S. The control device DC, the relay switch R, the feeder AL and the sensor S can also be integrated in a single control unit of the pump.

In a further version of the present invention, the infrared ray sensor is associated with a temperature sensor element, preferably integrated in the infrared ray sensor so as to constitute a single sensor unit having a twofold function either of level and temperature sensor. The function of this temperature sensor element is to detect possible overheatings of the pump, that can be caused by a breakdown of the electric motor of the electropump or by anomalous working conditions, as for example an extended idle operation, that is with the outlet valve closed.

The temperature sensor element, for example, can be installed directly in contact with the body of the electropump, so as to have the highest sensibility to the temperature variations of the electropump EP body, but can be also installed closely near the body of the electropump EP. In this case, the temperature sensor element does not detect the actual temperature of the eiectropump EP body, but a temperature representative of the temperature of the electropump EP body. The temperature sensor element can be an active element such as, for example, a thermocouple, that generates a signal, for example of electric type, proportional to the detected temperature, or a passive element, such as for example a thermic resistor or a thermistor, having a physical property, in this case the electric resistance, that varies proportionally to the temperature. Also the temperature sensor element is operatively connected to the control device DC, that detects, through the variations of the signal emitted by the temperature sensor element or through the variations of the above mentioned physical property of the sensor element, the variations of the temperature detected by the temperature sensor element and operates the relay switch R, in order to break off the supply of the electropump when the detected temperature overcomes a preestablished value.

The infrared ray sensor, with the integrated temperature sensor element if necessary, can be installed into the outlet duct of the pump P, in order to signal the absence of fluid into the outlet duct, which indicates a suction deficiency of the pump, and, if required, anomalous variations of the temperature of the liquid in the pump, which indicate overheating of the pump or of the respective electric motor.

In a further advantageous version of the present invention, the supply of the infrared ray sensor is performed intermittently, at preestablished time intervals, through a timer element inserted in the control device DC. This is possible because the variation of the level of the liquid in the well or the tank, in which the electropump EP is installed, is always relatively slow, so that it is not necessary to monitor the fluid level continuously, but it is enough to monitor it at intervals of time, by properly choosing the duration of the interval between an activation of the sensor S and the subsequent activation, dependently on the maximum speed of variation of the level of the liquid.

Similarly, also the temperature detection of the electropump EP body, through the temperature sensor element, can be performed at preestablished time intervals.

When said timer element is used, the control device DC may be set in such a way as to activate or deactivate the relay switch R only when the sensor S detects the presence or the absence of the liquid at the preestablished depth, during a preestablished number of consecutive activations of the sensor S.

This in order to prevent oscillations of the level L of the liquid, caused by temporary and casual perturbations, when the level L is near said preestablished depth, from causing consecutive frequent activations and deactivations of the pump P, that could damage the pump P, or its motor.

The control system according to the invention does not apply obviously only to submersible pumps, as in the embodiment examples described above, but can be applied to any type of pumps, for examples to pumps installed into environments that can be subjected to inundation said pumps being activated only when a liquid is present in said environment, to pumps installed into autoclaves, to pumps for waste waters and to pumps used in general for drawing a liquid from a container and transferring it elsewhere.

Furthermore, the system according to the invention can be installed also in any hydraulic circuit, for example into a lubrication circuit or into a cooling circuit, by using the infrared ray sensor S and the temperature sensor element for monitoring fluid level and temperature in said circuit.

Furthermore, the signals generated by the infrared ray sensor S and the temperature sensor element can be used both to deactivate or activate a pump P that circulates a liquid into a hydraulic circuit and to activate or deactivate an alert signal, denoting anomalous operating conditions of the hydraulic circuit, as for example insufficient amount of liquid into the circuit or overheating of the liquid, which is particularly advantageous, for example, when lubricating and cooling circuits of general equipments, or motor-vehicles are concerned.

In the practical embodiments, the materials, the dimensions and the construction details can be different than indicated, but technically equivalent thereto, without leaving the juridical domain of the present invention.