SAFETY VALVE FOR RELEASING GAS IN OVERPRESSURE, PARTICULARLY FOR LPG VEHICLES PROPULSION APPARATUS

The present invention relates to a safety valve for releasing gas in overpressure, particularly for LPG vehicles propulsion apparatus. As is known, in order to avoid the danger of explosion of the LPG tanks equipping motor vehicles, suitable safety devices have been devised which, in emergency conditions, such as a sudden increase in the internal pressure of the tank due to a fire, are capable of evacuating a large quantity of gas in a very short time.

The simplest safety device substantially consists of a spring-loaded valve, which is integrated in the multipurpose valve and is constituted by a chamber which is connected to the outside environment and to the inside of the tank and by a flow control element which is pushed by a spring.

While in normal pressure conditions the flow control element closes the connection between the inside of the tank and the outside environment, in case of overpressure the gas overcomes the action of the spring, moving the shutter so as to free the opening and evacuate externally.

Other conventional devices include a spring-loaded valve, of the type described above, and a fusible element which is inserted within the body of the multipurpose valve, so as to close the connection between the inside of the tank and the outside environment.

In case of overpressure caused by a fire, the gas is evacuated both through the spring-loaded valve and through the duct freed by the fusible element, which melts when a temperature of approximately 120 ⁰ C is reached.

Italian Patent No. 1315175 discloses a safety device constituted by a double spring- loaded valve which is integrated in the multipurpose valve. The valve is constituted by a chamber which is closed by a fusible plug and is connected both to the outside environment and to the inside of the tank. The valve also comprises a flow control element which is pushed by a first spring arranged inside the chamber and by a second spring located within the tank. In normal pressure conditions the flow control element closes the opening connecting the inside of the tank and the outside environment under

the thrust of both springs, while in case of fire the fusible plug melts, releasing the first spring, and the gas in overpressure moves the flow control element, overcoming the action of the second spring, and evacuates externally.

Italian Patent No. 1315578, discloses a safety device constituted by another type of spring-loaded valve integrated in the multipurpose valve. Such valve is constituted by a chamber which is connected to the outside environment and to the inside of the tank, by a flow control element, which is pushed by a spring located inside the chamber, and by a fusible insert, which is inserted in the side walls of the chamber. In normal pressure conditions, the flow control element closes the opening connecting the inside of the tank and the outside environment by way of the thrust of the spring; vice versa, in case of fire, the gas in overpressure evacuates externally both through the hole released by the melting of the fusible insert and by moving the flow control element after overcoming the action of the spring.

Although the above described devices are able to ensure the required safety conditions, they are not optimized from the structural standpoint and are therefore bulky and scarcely advantageous from a merely economical standpoint.

The above described device with the double spring-loaded valve necessarily entails the use of two springs and requires the installation of one of the two springs inside the tank, while the other devices, constituted by the single spring-loaded valve and by a separate fusible insert, appear particularly complicated to manufacture.

The aim of the present invention is to overcome the drawbacks of the cited prior art by, providing a safety valve which, in overpressure conditions, is capable of evacuating from a tank a large amount of gas in a very short time.

Within this aim, an object of the invention is to provide a safety valve which integrates, in a single structure, a fusible device and a spring-loaded valve, reducing space occupation and difficulties in production.

Another object of the invention is to provide a safety valve which can be integrated in a multipurpose valve.

Another object of the invention is to provide a safety valve which is suitable for current regulatory requirements.

Another object of the invention is to provide a safety valve which is simple to provide, quick to install, and is advantageous from a merely economical standpoint.

This aim and these and other objects, which will become better apparent hereinafter, are achieved by a safety valve for releasing gas in overpressure, comprising a cylindrical chamber provided with a plurality of lateral holes and with at least one opening which is provided on the bottom of said cylindrical chamber in order to be connected to the inside of a tank which contains said gas, said cylindrical chamber accommodating a flow control means which is kept in abutment against said opening by an elastic member, characterized that it comprises at least one fusible device which is joined to the top of said cylindrical chamber in order to keep said elastic member compressed and contrast the thrust of said gas exclusively in normal pressure and temperature conditions.

Further characteristics and advantages will become better apparent from the description of a preferred but not exclusive embodiment of a safety valve according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is an exploded sectional view of a safety valve according to the invention; Figure 2 is a sectional view of the safety valve according to the invention, in normal pressure and temperature conditions;

Figure 3 is a sectional view of the safety valve according to the invention in case of fire.

With reference to the figures, the safety valve, generally designated by the reference numeral 1 , comprises a cylindrical chamber 2, provided with lateral holes 3 which are connected to the outside environment, and with an opening 4 provided on the bottom of the cylindrical chamber 2 so as to be connected to the inside of a multipurpose valve 60, of which the safety valve 1 is an integral part.

The multipurpose valve 60 is connected to the inside of a tank, not shown in the figures, in which the gas 70 is stored.

A flow control means 5 is accommodated within the cylindrical chamber 2 and is kept in abutment to the opening 4 by an elastic member in order to prevent the exit of the gas 70 from the multipurpose valve 60 when in normal pressure and temperature conditions.

The elastic member is preferably constituted by a spring 6. The flow control means 5 comprises a bush 7 which has a square cross-section, provided with a sealing member which is preferably constituted by a pad of elastomer 8, and is provided with a receptacle

9 which is suitable to accommodate the spring 6. According to the invention, the safety valve 1 comprises a fusible device which is joined to the top of the cylindrical chamber 2 so as to keep the spring 6 compressed and contrast the thrust of the gas 70 only in normal pressure and temperature conditions.

In practice, the fusible device is constituted by a cylinder 10 made of a low-melting alloy, which is accommodated within an adjustment screw 11 which is associated with the top of the cylindrical chamber 2 so as to allow to adjust the compression of the spring 6.

The direct contact between the cylinder 10, made of low-melting alloy, and the spring 6 is prevented by a metal disk 12 which is interposed between them.

A plurality of through holes 13 are provided at the head of the adjustment screw 11 ; such through holes 13 allow the metal disk 12 and the spring 6 to extrude the cylinder 10 made of low-melting alloy if it melts due to an increase in temperature. Operation of the safety valve according to the invention is as follows. In normal pressure and temperature conditions, the flow control means 5 prevents the gas 70 from escaping from the multipurpose valve 60 through the opening 4, by virtue of the force applied by the spring 6.

If the pressure of the gas 70 increases until the level preset by regulatory requirements is reached, the flow control means 5 rises and frees the opening 4, allowing the gas 70 to exit from the multipurpose valve 60 and to disperse into the outside environment, passing laterally with respect to the bush 7 and flowing out through the lateral holes 3.

In case of fire, when a temperature of approximately 120°C is reached, the cylinder

10 made of low-melting alloy melts and, by virtue of the force applied by the spring 6 to the metal disk 12, which acts as a piston, is extruded through the through holes 13.

As a consequence, in practice the compression of the spring 6 is eliminated; by no longer contrasting the force applied by the gas 70 in overpressure, this allows the flow

control means 5 to rise freely and open the opening 4, so as to allow the rapid escape of all the gas 70 from the multipurpose valve 60 and therefore from the tank.

In practice it has been found that the safety valve according to the invention fully achieves the intended aim, since in overpressure conditions it is able to evacuate a large quantity of gas from a tank, in a very short time, in compliance with current regulatory requirements.

Also, the safety valve according to the invention can be an integral part of a multipurpose valve, and is simple to manufacture and quick to install. The present valve is capable of integrating a fusible device and a spring-loaded valve, reducing space occupations and difficulties in production.

This application claims the priority of Italian Patent Application No. VI2007A000204, filed on July 18, 2007, the subject matter of which is incorporated herein by reference.