Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
2000-08-08
2002-01-15
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
Reexamination Certificate
active
06338268
ABSTRACT:
BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION
It has been found that a rudimentary, hanging-water-tube, vacuum-test results correlates well enough with a frequency method of determining the relative leak rate of a check valve to verify the existence of a relationship between the two. The frequency results, compared to a commercial leak rate tester which measures the mass flow at 2 psi vacuum as shown in FIG.
1
. This is a very good correlation in the world of leak detection.
It turns out that check valve devices having noncompliant mating surfaces and stringent leakage requirements are measured by applying a hard vacuum (14.7 psi) and measuring the small leakage (10
−3
to 10
−9
cc/sec of air) via a helium gas tracer. Devices having compliant mating surfaces and less stringent requirements are measured by applying a smaller pressure or partial vacuum and directly measuring the mass flow of the leakage in the greater than 10
−3
cc/sec range.
Mating surfaces of rubber, plastic, etc., fall into the compliant category so that the leak performance would be vastly improved if tested with a hard vacuum, but the results are unobtainable in practice. As may have been expected, these “soft-surfaced” devices usually experience relatively small pressure differentials in practice so that hard vacuum techniques are not appropriate. Mass flow meters are used to directly measure the leakage from these soft-surface devices at the low-pressure differentials experienced in practice.
A general current trend is that soft-surfaced devices are chosen because they are forgiving in spite of loose tolerances, but the acceptance criteria are by demand creeping toward more stringency. For example, the acceptable check valve samples above are in the 10
−3
to 10
−4
range. This is just beyond the mass flowmeter's capability. It is believed that the present invention's frequency technique will detect leaks into the 10
−5
cc/sec range.
Currently, the frequency method has been shown to operate around the 10
−3
range and has the advantage of being very fast in reading (under one second). The testing hardware and software are economical compared to that of the current methods, and there is minimal stress placed on the compliant seat materials.
Valve
Many spring-loaded valves/closures are inherently unstable and therefore oscillate when operated with air in a direction to force them open.
FIG. 2
shows a ball check valve in three stages of opening.
The left sketch of
FIG. 2
shows the ball just at the point of opening where the pressure force Fp is just equal to the spring force Fk. The inertial force of the ball Fi is zero at this instance.
The middle sketch of
FIG. 2
shows the gap h opened to less than 0.001 inches. Because the flow is in the capillary regime, the pressure force Fp acts counter to the spring and inertial forces so that the motion of the ball is upward.
In the right sketch of
FIG. 2
, the gap h has opened in excess of 0.001 inches and channel flow commences. Here the pressure rapidly diminishes (sometimes goes negative) and the pressure force Fp becomes less than the sum of the spring and inertial forces so that the ball decelerates its upward motion and reverses to move toward the seat. As the ball nears the seat (within h<0.001 inches), the pressure rises quickly (being proportional to h
3
) and the ball bounces on the air film to again reverse and take an upward turn, completing one cycle of oscillation.
As can be seen, the dynamics of the oscillation will be dependent, at the extremely small-gap part of the cycle, on the detailed geometry of the ball and seat at their interface. When the mating parts of the sealing surface contain an imperfection such as a small scratch, the frequency of oscillation will be slower than that of a more perfect set.
Non-Oscillating Devices and the Present Invention
In some cases using very compliant materials such as rubber, the sealing device can be non-oscillating or oscillate so weakly that frequency detection is impractical. In the present invention, a fluid element is configured so that it oscillates owing to being back-loaded.
An object of the invention is to provide an improved leak detection method and apparatus.
Another object of the invention is to provide an improved fluidic detection method and apparatus.
REFERENCES:
patent: 4709622 (1987-12-01), Stouffer et al.
patent: 5396808 (1995-03-01), Huang et al.
patent: 5780738 (1998-07-01), Saunders
patent: 5864067 (1999-01-01), Ligneul et al.
patent: 5889213 (1999-03-01), Guizot et al.
patent: 5983943 (1999-11-01), Parry et al.
patent: 703888 (1996-01-01), None
patent: 2120384 (1983-11-01), None
Bowles Fluidics Corporation
Politzer Jay L.
Williams Hezron
Zegeer Jim
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