Fluid handling – Systems – System with plural openings – one a gas vent or access opening
Reexamination Certificate
2000-02-17
2001-01-16
Chambers, A. Michael (Department: 3753)
Fluid handling
Systems
System with plural openings, one a gas vent or access opening
C137S494000, C137S907000, C123S510000
Reexamination Certificate
active
06173741
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a pressure compensating valve for a fuel tank, in particular for a fuel tank of a work tool such as a motor-driven chain saw, cutoff machine, brushcutter, et cetera, driven by an internal combustion engine. Such a pressure compensating valve includes a pressure compensating channel opening into the tank interior. The pressure compensating channel can be closed off by a valve body seated seal-tight on a valve seat. The valve body lifts off the valve seat when an underpressure is present within the tank interior to open the pressure compensating channel to the atmosphere.
BACKGROUND OF THE INVENTION
Pressure compensating valves for fuel tanks are known in several configurations. For example, U.S. Pat. No. 5,526,843 discloses a mushroom-shaped valve body made of a rubber-elastic material having an outer head portion resting seal-tight against the valve seat. In order to ensure pressure compensation of the tank interior at minimal underpressures, the valve body must therefore be of soft-elastic material. However, this entails problems when overpressures are present because the valve body then yields easily and can become deformed so that leaks may occur.
The minimal closing forces of the mushroom-shaped valve at normal pressure also entail the risk that a proper closing and opening of the mushroom-shaped valve can no longer be ensured when residues, foreign bodies, et cetera, are deposited on the valve seat.
SUMMARY OF THE INVENTION
The invention has the object to improve an pressure compensating valve of the above-mentioned kind such that it opens and permits pressure compensation already at minimal underpressures but is reliably closed at overpressures without mechanically overloading the valve.
The pressure compensating valve arrangement of the invention is for a fuel tank and defines a tank interior wherein an underpressure can develop. The arrangement includes: a housing defining an interior space; a membrane mounted in the interior space so as to define a control chamber therein bounded by the membrane; a pressure compensating channel opening into the control channel and communicating with the tank interior; the membrane having a first side facing toward the control chamber and the tank interior and a second side facing away from the control chamber; a reference pressure source for charging the second side of the membrane with a reference pressure; the membrane being a deflectable membrane which deflects in response to the underpressure when the underpressure is less than the reference pressure; a valve unit mounted in the housing and defining an interface between the control chamber and the ambient atmosphere; the valve unit including a valve seat defining a passage between the ambient atmosphere and the control chamber; and, a valve body moveable between an open position wherein the tank interior communicates with the ambient atmosphere via the control chamber to allow air to flow in a flow direction from the ambient atmosphere into the tank interior and a closed position wherein the valve body rests seal tight against the valve seat to seal off the tank interior from the ambient atmosphere; and, connecting means for operatively connecting the valve body to the deflectable membrane so as to cause the valve body to move into the open position from the closed position in response to the deflection of the membrane caused by the underpressure thereby allowing air to flow in the flow direction into the fuel tank.
The control of the valve body via a membrane charged by the pressure within the fuel tank ensures, on the one hand, a safe sealing action at overpressures and, on the other hand, an adjusted pressure compensating action at underpressures. A fine-tuned valve response is adjustable via the dimensions of the membrane even at minimal underpressures.
The valve body is suitably held in the closed position by a spring. The biasing force of the spring is selected according to the desired opening pressure of the pressure compensating valve. The valve body can be configured as a plunger which is longitudinally moved for closing or opening the valve. In a preferred embodiment of the pressure compensating valve of the invention, the membrane is fixedly connected to a membrane plate which is operatively connected to the valve body via a two-arm valve lever. When the pressure in the control chamber drops below a predetermined difference value relative to the reference pressure, thus causing the membrane to be moved counter to the biasing force of the spring, the membrane plate moved with the membrane actuates the valve plunger by pivoting the valve lever.
A simple configuration of the pressure compensating valve is realized when the ambient pressure acts as a reference pressure on the membrane. The reference volume at the side of the membrane facing away from the control chamber communicates with the atmosphere.
The valve is very responsive when the cross section of the control chamber acting on the membrane is a multiple greater than the pipe cross section of the pressure compensating line closeable by the valve. In addition to selecting the dimensions of the membrane, the adjustment of the responsiveness of the pressure compensating valve can also be adjusted via the lengths of the lever arm of the valve lever and/or the biasing force of the valve spring.
REFERENCES:
patent: 2631600 (1953-03-01), Flanagan
patent: 2675793 (1954-04-01), Ziege
patent: 2946341 (1960-07-01), Sullivan
patent: 2988097 (1961-06-01), Benzel
patent: 3746036 (1973-07-01), Bois et al.
patent: 3974851 (1976-08-01), Garrelson
patent: 709488 (1931-05-01), None
Andreas Stihl AG & Co.
Chambers A. Michael
Ottesen Walter
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