Pumps – With condition responsive pumped fluid control – Pressure responsive relief or bypass valve
Reexamination Certificate
1999-11-16
2001-11-20
Freay, Charles G. (Department: 3746)
Pumps
With condition responsive pumped fluid control
Pressure responsive relief or bypass valve
C417S440000, C137S536000
Reexamination Certificate
active
06318973
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a fuel pump for supplying fuel to reciprocating aircraft engines and the like and more particularly to the configuration of the seals used to prevent overboard leakage of fuel at the interfaces between the valve housing and mating parts.
BACKGROUND OF THE INVENTION
Fuel pumps used to supply fuel to reciprocating aircraft engines are driven through suitable drive couplings between the pumping element and associated gear boxes inside the engines.
Because this type of pump is a positive displacement pump, the fuel output of the pump is usually greater than the fuel flow requirements of the engine or aircraft system downstream of the pump. Any excess flow is typically routed from the high pressure side of the pump back to the low pressure side through an integral bypass valve.
To prevent overboard leakage of fuel between the pump housing and mating valve housing, a flat elastomeric gasket is conventionally used to provide a seal at the pump housing/valve housing interface. In addition, a diaphragm seal is conventionally clamped between the valve housing and associated valve cover to prevent leakage at this interface.
Although such seal arrangements have generally performed quite satisfactorily over the years, their ability to prevent overboard leakage of fuel under all operating conditions is sensitive to assembly technique, compression set resistance of the elastomeric gasket and diaphragm seal, and operating temperatures. The gasket and diaphragm seal are susceptible to compression set when exposed to high thermal stresses with a corresponding reduction in the compressive pre-load on the gasket and diaphragm seal once the thermal stresses are relieved, resulting in a greater potential for a fuel leak path through the clamped joints.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, a novel seal arrangement is provided between the valve housing and mating pump parts for maintaining the necessary sealing function therebetween regardless of joint clamping forces.
In accordance with another aspect of the invention, an O-ring seal is used to provide sealing contact with a diaphragm seal between the valve housing and valve cover interface despite some loss of clamping load.
In accordance with another aspect of the invention, a molded O-ring type ladder seal is used in place of the usual gasket between the valve housing and pump housing interface to maintain seal integrity in the event of some loss of clamping load.
In accordance with another aspect of the invention, such O-ring type seals function as long as the gland clearances are maintained with a relatively loose tolerance band compared to the squeeze tolerance required for a gasket to maintain a fluid seal between mating parts.
In accordance with another aspect of the invention, machined O-ring grooves are provided in opposite sides of the valve housing to capture and maintain a controlled squeeze of the O-ring against the diaphragm seal and the molded O-ring type ladder seal against the pump housing.
In accordance with another aspect of the invention, the valve housing with machined O-ring grooves is fabricated from wrought aluminum.
In accordance with another aspect of the invention, both the O-ring type ladder seal between the valve and pump housing interface and the standard O-ring seal against the diaphragm seal are made of a fluorocarbon material.
In accordance with another aspect of the invention, the valve housing with machined O-ring grooves is completely interchangeable with valve housings of pad mounted fuel pumps currently in service to permit such pumps to be retrofitted in the field by substituting the valve housing with O-ring grooves for the existing valve housing and removing the gasket between the valve housing and pump housing and replacing it with an O-ring type ladder seal and adding a standard O-ring against the diaphragm seal.
In accordance with another aspect of the invention, alien head valve cover screws are used in place of the usual slotted head valve cover screws to eliminate the potential for stripping of the screw heads during assembly and provide a visual indicator that fuel pumps currently in service have been retrofitted with a valve housing with machined O-ring grooves and associated O-ring type seals.
These and other aspects, advantages and features of the present invention will become apparent as the following description proceeds.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.
REFERENCES:
patent: 2680031 (1954-06-01), Barr
patent: 4408964 (1983-10-01), Mochizuki et al.
patent: 4768888 (1988-09-01), McNaull
patent: 5059099 (1991-10-01), Cyphers
patent: 5290152 (1994-03-01), Wallace et al.
patent: 5520155 (1996-05-01), Hefler
patent: 5765835 (1998-06-01), Johnson
Beligoy Kenneth M.
Sailer Thomas
Crane & Co.
Freay Charles G.
Gray Michael K.
Renner , Otto, Boisselle & Sklar, LLP
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