Abstract:
A venting valve connected to the interior of the fuel tank has a sliding piston and a plurality of springs which hold the piston in different operative positions dependent upon the amount of pressure within the tank.

Description:
BACKGROUND OF THE INVENTION 
     This invention pertains to venting devices for diesel fuel tanks of the type having heated excess fuel returning to the tank. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an inexpensive fuel tank vent which will not leak fuel during impact spurts or overturning of the vehicle, will allow inward passage of air to replace consumed fuel and will vent high-pressure gases from within the tank during normal running operations and excessive pressure conditions. 
     Basically these objects are obtained by providing a main body having discharge ports and communicating with the interior of the fuel tank. Within the main body is a slidable piston having ports which will communicate with the discharge ports during different operative conditions. A pair of springs or a dual spring rate spring means holds the piston in different positions with the lighter spring aligning the ports during normal excess fuel conditions of the engine and the greater spring rate disaligning the ports during excessive fuel spurts to prevent leakage of fuel from the tank. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING 
     FIG. 1 is a diametrical section through the fuel tank vent embodying the principles of the invention. 
     FIG. 2 is a transverse section taken along the line 2--2 of FIG. 1. 
     FIGS. 3A-3D are schematic operational views of the fuel vent. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The fuel tank venting valve includes a main body 10 having flats 12 in which are provided discharge ports 14. The discharge ports communicate with a cylindrical interior wall or bore 16 that connects via passage 18 to the interior of the fuel tank 20. 
     Slidably positioned within the bore 16 is a cylindrical piston 22 having radial ports 24 that communicate with an internal passage 26. The passage 26 communicates with the passage 18 in the main body. 
     The piston is held in its positions by a pair of springs including a lightweight spring 30 and a heavier spring 31. As best seen in FIG. 1 the heavy spring is not engaging the end wall of a cap 32 which is threadably secured to the main body. The gap between the heavy spring 31 and the cap allows the lighter weight spring 30 to control the position of the piston during lighter internal pressures inside the tank 20. The amount of spring force applied can also be varied by the position of the cap 32 relative to the main body 10. 
     The operation of the valve is best shown in the schematic FIGS. 3A-3D. In FIG. 3A the piston is shown in a position in which there is no or little internal pressure within the tank. Air from the exterior of the tank can pass through the ports 14, pass between the piston and the cylindrical surface 16 and enter the tank to make up for the volume of fuel consumed by the engine. This assures that the tank is not subjected to excessive vacuum pressure. The volume of air required is very small (about 1 cu. ft. per hour) and is caused by less than 1/2 pound psig vacuum. This small amount of air can leak between the piston and the cylindrical surface whereas larger amounts of air or hot gases or fuel cannot readily pass between the piston and the cylindrical surface. 
     In FIG. 3B the piston is shown such that the ports 14 and 24 are in alignment and the spring 30 slightly compressed. This condition occurs during normal running operations of the vehicle. The diesel engine receives considerable more fuel than it consumes and returns the excess fuel to the tank. This excess fuel is heated in the engine and mixed with hot combustion gases so that the returning volume is about 0.5 cu. ft. per min. causing a pressure to the tank is in the vicinity of 2 to 3 psig. These expanded gases and combustion gases are thus free to be vented to the atmosphere. 
     FIG. 3C shows a condition where there is a transient high-pressure spike such as about 30 psig. This occurs from a crash or other impact against the fuel tank and shifts the piston upwardly compressing the heavier spring 31 so that liquid fuel cannot pass out of the discharge ports 14. 
     FIG. 3D shows a pop-off condition which occurs when the internal pressure in the tank approaches the structural strength capability of the tank approximately 50 psig. When the pressure reaches this amount, the larger spring 31 is compressed with the piston sliding past the ports 14 to completely relieve the fuel tank. 
     The remaining condition is an overturn situation with the small spring 30 being capable of holding the piston fully closed to withstand the pressure of the fuel in the tank which is approximately 2 psig. 
     As is readily apparent, the vent valve is very simple in construction but serves a multitude of safety functions. While the preferred embodiment of the valve has been illustrated and described, it should be understood that variations will be apparent to one skilled in the art without departing from the principles herein. Accordingly, the ininvention is not to be limited to the specific embodiment illustrated in the drawing.