It is known that in the oil burners, before the starting, it is necessary to carry out the prewashing and the preheating so as to establish the optimum conditions to start the combustion.

For this purpose in the preheating phase the petroleum naphtha is circulated and goes through the tank to the atomizers which, being of the mechanic operation type, are kept closed because of the push which is generated on the pins by a spring.

Once the preheating phase has ended, through the move of solenoid valves the circulation of the petroleum naphtha is interrupted, the circuit is put under pressure, the pins of the atomizers open and carry out the atomizing of the petroleum naphtha and the starting of the burner.

But the use of circuits of the descripted type presents the drawback that during the prewashing phase, since the return lines of the burner are cold, they offer a big resistance to the passage of the petroleum naphtha which can cause water hammering and the consequent opening of the atomizer pins and therefore false startings blocking the burner.

Moreover the circuits of the known type present also a certain structural complication since they imply the use of several solenoid valves and of complex petroleum naphtha paths, causing hot petroleum naphtha leaks because of the blow-by.

The present invention intends to overcome the said drawbacks.

Particularly one of the aims of the invention is to realize an improved hydraulic circuit for stoking, prewashing, preheating and atomizing the petroleum naphtha in a burner which on the structural side can be realized in a simpler manner as regards the equivalent circuits of the known type.

It is a further aim that the improved hydraulic circuit which is the object of the invention presents also a more reliable working as regards the equivalent cycuits of the known type.

The said aims are attained through the realization of an improved hydraulic

circuit for stoking, prewashing, preheating the petroleum naphtha in a burner which according to claim one includes: -a fuel pump which is provided with a suction pipe picking the petroleum naphtha contained in a tank; -a pressure regulator presenting the inlet which is connected through a first pipe to the delivery orifice of said pump; -a preheater presenting the inlet which is connected through a second pipe to the outlet of said pressure regulator; -a gasproof valve presenting the inlet which is connected through a third pipe to the outlet of said preheater; -a valve unit for the stoking of said bumer and the biow-by of the petroleum naphtha in said tank, which is connected through a fourth pipe to the outlet of said gasproof valve, and is characterized in that said valve unit includes at least a valve for the stoking of said burner the inlet whereof is connected to said fourth pipe deriving from said gasproof valve and is connected in series to at least one valve for the blow-by of said petroleum naphtha the outlet whereof is connected to a pipe for the return of said petroleum naphtha to said tank.

According to a preferred embodiment said valve unit includes: -two stoking valves of the usually closed type which are connected in parallel one to the other, each one being suitable for stoking one of the stages of said burner; -a blow-by valve of the usually open type which is connected in series to said stoking valves.

Said stoking valves and said blow-by valve are valves of the solenoid control type.

Advantageously the improved hydraulic circuit of the invention presents also a lower realization cost and higher working reliability, in addition to its simpler realization as regards equivalent circuits of the known type.

The said aims and advantages will be better underlined during the description of a preferred embodiment of the invention referring to the enclosed drawings where: -fig. 1 shows the circuit of the invention during the prewashing and preheating phase; -fig. 2 shows the improved hydraulic circuit of the invention at the end of the

prewashing and preheating phase; -fig. 3 shows the improved hydraulic circuit of the invention during the opening phase of one of the stoking valves; -fig. 4 shows the improved hydraulic circuit of the invention during the opening phase of both the stoking valves.

As it can be observed in fig. 1 the improved hydraulic circuit of the invention, marked with 1 as a whole, is formed by: -a stoking pump 3 connected to a suction pump 4 provided with a filter 5 picking in a tank, which is not represented in figure, containing petroleum naphtha; -a pressure regulator, marked with 6 as a whole, presenting the inlet 61 connected through a first pipe 62 to the delivery orifice 31 of said pump 3; -a preheater, marked with 7 as a whole, presenting the inlet 71 connected through a second pipe 72 to the outlet 63 of said pressure regulator 6; -a gasproof valve, marked with 8 as a whole, presenting the inlet 81 connected through a third pipe 82 to the outlet 72 of said preheater 7 with the interposition of a filter 73; -a valve unit marked with 9 as a whole realizing the stoking of a burner 2, and connected through a fourth pipe 83 to the outlet of said gasproof valve 8.

It can be observed that said pressure regulator 6 presents a third way 64 which is connected to a pipe 65 for the return of the petroleum naphtha in the tank.

More particularly said valve unit 9 is formed by a first stoking valve 91, by a second stoking valve 92 and by a blow-by valve 93 which, as it can be observed, are all connected in series one to the other so as to connect said fourth pipe 83 with said return pipe 65.

It can be observed that all these three valves are of the solenoid control type respectively 191,192,193 and whereas both the stoking valves 91 and 92 are of the usually closed type, the valve 93 is of the usually open type.

During the prewashing and preheating phase, the petroleum naphtha circulates as represented in fig. 1 where it can be observed that the suction caused by the pump 3 makes the petroleum naphtha deriving from the tank flow in the suction pipe 4 according to the direction 41 in order to make it go through the first pipe 62 with the direction 621.

Therefore the petroleum naphtha goes in the pressure regulator 6 going through the inlet 61 and it goes through the outlet 63 in the second pipe 72

running through it with the direction 721 toward the preheater 7.

The exceeding petroleum naphtha flow rate, through the third orifice 64 of the pressure regulator 6, flows with the direction 651 in the return pipe 65and goes again in the tank.

The petroleum naphtha goes through the second pipe 72, goes in the preheater 7 through the inlet 71 and comes out preheated through the outlet 72, therefore going in the gasproof valve 8 through the inlet 81 after having gone with the direction 821 through the third pipe 82 connecting said preheater 7 to said gasproof valve 8.

The petroleum naphtha comes out from the gasproof valve 8 through the outlet 84 and going through the fourth pipe 83 with the direction 831 it goes in the valve unit 9 and particularly in the inlet 291 of the first stoking valve 91.

The valves 91 and 92 being both of the usually closed type whereas the blow- by valve 93 is of the usually open type, a petroleum naphtha flow originates through the valve unit 9 with the direction 900 which, through the inlet 291 of the first stoking valve 91, goes in and through all the three valves which are placed in series one to the other and, through the outlet 293 of the blow-by valve 93 and the return pipe 65, it goes in the tank again.

Therefore the petroleum naphtha circulates in a closed circuit without coming to the burner 2 during the time which is needed so that the petroleum naphtha and the circuit pipes reach the suitable temperature to start the combustion.

After having reached said optimum temperature, the blow-by valve 93, as it can be observed in fig. 2, is closed operating the solenoid 193 controlling it so that it interrupts the petroleum naphtha flow through the direction 615 along the return pipe 65 which brings it back in the tank.

Therefore the petroleum naphtha flow jams against the stoking valves 91 and 92.

If from now on, as it can be observed in fig. 3, the solenoid 191 of the first stoking valve 91 is excited, the stoking valve 91 is opened and through it a flow 911 introducing the petroleum naphtha which is under pressure in the first stage of the bumer is produced. The combustion starts just now.

If the starting of the second stage of the burner is wanted, the solenoid 192 of the second stoking valve 92 should be excited so that, as it can be observed in fig. 4, the stoking valve 92 too is opened so that it produces a petroleum naphtha flow 921 stoking the second stage of the burner 2.

During the opening of one or of both said stoking valves 91 and 92, the petroleum naphtha circulation takes place, referring to fig. 3 and 4, along the directions 41,621,721,821,831,911 and 921, without any blow-by of the petroleum naphtha returning in the tank along the return pipe 65, leaving aside the possible amount which is blown-by through the third way 63 of the pressure regulator 6.

Closing both the stoking valves 91 and 92, the petroleum naphtha stoking to the bumer jams and the flame is extinguished.

It is understandable according to what has been said that the circuit of the invention attains actually all the established aims.

First of all the executive simplicity of the circuit limiting at the least the number of pipes which are used and therefore quickening the prewashing and preheating operations can be observed.

Moreover since stoking and blow-by valves which are provided with solenoid direct control are present, the system working as a whole is made even more reliable since the control of each one is entrusted only to the presence or the absence of a solenoid electric signal for the control of each valve.

In the executive phase the circuit of the invention can experience variations such as the presence of three stoking valves or only one instead of the two described valves, according to the installation of a three stages burner or a single-stage one instead of a two-stage one as in the descripted executive form.

As regerds the dimensions, the flow rates and the types of the used valves as well as the size of the circuit elements such as the pump, the pressure regulator, the preheater and the gasprrof valve, these ones can be of any type.

However it is stated that other variants which have not been quoted here, if they are based on the same described executive idea, are to be considered as protected by the present patent.