Patent Application
20070102341
This invention relates to a wash flow filter for fuel filtration which utilizes plural parallel tubes.
Fuel systems, in particular for aircraft applications, require relatively clean fuel. Wash flow filters are commonly used in fuel systems to provide maintenance free systems for filtering contaminants from fuel. The filters are typically cylindrical or conical in shape. Fluid flow enters the cylinder at one end and flows out an opposing end. The cylinders are formed from a screen material to act as a filter. As the fluid flows through the cylinder some of the fluid passes radially out through the screen. Contaminants within the fuel are caught by the screen and remain within the cylinder. The fluid that has exited radially from the cylinders is filtered fuel. As other fluid flow continues to pass along the cylinder, it removes the contaminants from the screen to provide a self-cleaning filter.
The requirements of the fuel system determine the size of the wash flow filters. The surface area of the screen governs the amount of filtration obtained by the filter. Additionally, the velocity of the fluid passing through the filter is critical for washing the contaminants from the filtering material. Fluid velocity is controlled by the diameter of the cylinder. Therefore, the velocity required for flushing the contaminants dictates the diameter of the filter. Because the diameter of the tube is limited, the variable for controlling the amount of filtration is the length of the cylinder.
As fuel system become more complex the amount of filtration required increases. Higher levels of filtration cause the length of the cylinder the filters to increase. Fitting the required filter within the available system space becomes a problem as the filter lengthens.
A wash flow filter that does not require increasing length to maintain a desired fluid velocity and filtration level is needed.
The fuel filter assembly of the present invention includes multiple tubes within a wash flow filter. The filter is assembled within a bore. Multiple tubes run from a first header to a second header. A first seal is located in the first header to prevent fluid outside the bore and within the tubes from mixing with fluid inside the bore and outside of the tubes. The second header has a second seal similar to the first seal.
Fluid enters the filter at a first end and exits the filter at a second end. The tubes are manufactured of a mesh or filter material. Thus, as flow passes through the tubes some of the fluid exits radially through the sidewalls of the tubes. The sidewalls filter particles out of the fluid as the fluid passes through to obtain a filtered fluid. As more fluid flows along the fluid path the particles blocked by the sidewalls are washed out the second end of the tube. Thus, the filter is self-cleaning. The washed fluid that has exited the tubes sidewalls is directed to a device requiring filtered fluid, such as an engine.
The fuel filter assembly has two distinct operating modes a conventional wash flow mode and a barrier filter mode. In “barrier” mode the axial flow through the filter is shut off forcing all flow to pass through the screen radially. During this time period, the screen collects all the contaminant that is larger than the minimum screen opening and proceeds to become clogged until the axial motive flow is re-instated allowing the wash mode to be re-established. Within a short period of time the screen is washed fully clean again.
The requirements of the fuel system determine the size of the filter. The component packaging determines the maximum diameter of the filter. However, the velocity of the fluid passing through the filter is critical for washing the contaminants from the filter. Velocity of the fluid is controlled by the diameter of the individual tubes within the filter.
The surface area of the sidewalls of the tubes governs the amount of filtration obtained by the filter as a whole. Because the component packaging is somewhat fixed the use of additional tubes provides benefits in design freedom. By adding additional tubes to the filter additional surface area of sidewalls is obtained without requiring undesirable lengthening of the filter and increased contaminant capacity when operated in barrier mode. The tubes may have a constant diameter cross-section. Alternatively, the cross-section may be reduced in diameter over the length of the tubes, such that the fluid velocity within the tubes remains relatively constant relative to the draw of radial washed fluid.
The use of multiple wash tubes allows for increased filter surface area, which allows greater contaminant capacity with minimal pressure drop, during barrier mode operation, allows for optimum filter tube sizing to obtain ideal wash velocities which ensures effective cleaning of the filter element and a more compact filter package for the given screen area, allowing for less weight than conventional packaging.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
The fuel filter assembly 12 has two distinct operating modes a conventional wash flow mode and a barrier filter mode. In one embodiment of a fuel system 10, the axial motive flow through the filter 14 is periodically shut off forcing all flow to pass through the tube 24 radially, indicated by arrows R. The fluid path F is closed off at the second end 38 to prevent fluid from exiting filter 14 into the outlet return 35 and passing back to the storage tank 32. This puts the screen into a pure “barrier” mode. During this time period, the screen collects all the contaminant that is larger than the minimum screen opening and proceeds to become clogged until the axial motive flow is re-instated allowing the wash mode to be re-established. That is the fluid path F at the second end 38 is opened. Within a short period of time the screen is washed fully clean again.
The surface area of the sidewalls 40 governs the amount of filtration obtained by the filter 14 and its contaminant holding capacity in barrier mode. In order to decrease the pressure drop during barrier mode and increase the contaminant holding capacity, additional tubes may be utilized within the filter assembly. By adding additional tubes 24 to the filter 14 additional surface area of sidewalls 40 is obtained without requiring undesirable lengthening of the filter 14. Also, the plurality of tubes keeps their diameter small and helps to maintain the desirable high fluid velocity during wash mode. Although, in the embodiment shown, there are four tubes 24, one skilled in the art would realize the number of tubes may vary for each application. The tubes 24 shown have a constant diameter cross-section. Referring to
The filter 14 is assembled by placing the first end 36 of the tubes 24 into the first header 20 and the second end of the tubes 24 into the second header 22. The first header 20 and the second header 22 are manufactured to have the one hole 42 for each required tube 24. Alternatively, the first end 36 of each tube 24 could be inserted into the first header 20 and then the second end 38 of each tube 24 could be inserted into the second header 22 until all the holes within the first header 20 and the second header 24 have a corresponding tube 24.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
