Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
2000-12-04
2002-09-24
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S040000, C073S049100
Reexamination Certificate
active
06453728
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for testing hollow pieces, such as pipes, etc., made of concrete, stoneware, casting, etc, in terms of their impermeability using a vacuum testing apparatus. Also, the invention relates to an apparatus for implementing the method, consisting of a support for the test piece and a medium for scaling the test piece on both sides. In particular, one of the sealing media is connected with a vacuum pump as well as with instruments for measuring the negative pressure.
The invention relies on known testing procedures for pipes made of stoneware, clay, concrete or similar porous materials. These procedures provide that both ends of the pipe are closed off with testing plates equipped with seals. If a negative pressure is created inside the test piece, that is sealed off on both sides, using the connected vacuum pump, it is possible to draw conclusions as to the grade of impermeability of the test piece based on the vacuum drop after the suction has been turned off. These conclusions are unreliable, however, if the internal pressure inside the test piece changes due to temperature variations after the suction is discontinued. Therefore, conducting a useful measurement is only possible once a stationary equilibrium with regard to the temperature has been reached.
Using methods of this kind is particularly disadvantageous in instances of fixed-cycle manufacturing because the required waiting time period for achieving the temperature equilibrium is too long. This time period is extended in particular by the thermal energy that is used for the adiabatic relaxation of the air while the vacuum is drawn. Another delay is caused by the evaporation of the water remaining in the pores which causes a cooling of the (rest) air content inside the test piece whereby a drop in pressure occurs which simulates an impermeability that does not in fact exist.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a class-specific method that accelerates the achieving of the temperature equilibrium, to reduce the testing time in fixed-cycle manufacturing; in addition, it is an object of the present invention to provide a class-specific apparatus for implementing the method that allows safe and undisturbed vacuum testing even in connection with short fixed-cycle times.
According to the invention this objective is achieved by a method for testing hollow test pieces for impermeability. The method comprises the steps of:
A) providing a gas in a vacuum in a compensation tank;
B) heating the gas provided in step A with a heater to a temperature substantially corresponding to a temperature of an inside wall of a test piece, whereby such gas constitutes temperature-controlled gas;
C) providing a gas at a vacuum in the test piece, which vacuum is at a level substantially corresponding to a value of the vacuum of the temperature-controlled gas in the compensation tank;
D) replacing the gas in the test piece with the temperature-controlled gas from the compensation tank;
E) adjusting the vacuum of the temperature-controlled gas supplied to the test piece in step D to a predetermined level; and
F) monitoring the vacuum level of the temperature-controlled gas in the test piece subsequent to step E for a predetermined period.
The invention also relates to an apparatus for testing hollow test pieces for impermeability. The apparatus includes a support for supporting a test piece, and two end plates for sealing opposite ends of the test piece. A compensation tank and a vacuum pump are provided. A first conduit arrangement is provided for selectively connecting the vacuum pump with one of the end plates and the compensation tank for providing gas at a vacuum selectively in the compensation tank and a test piece. A second conduit arrangement is provided for connecting the compensation tank with one of the end plates for replacing gas in the test piece with gas from the compensation tank. A first pressure measuring device measures pressure of gas in the compensation tank. A temperature measuring device measures temperature of gas in the compensation tank. A second pressure measuring device measures pressure of gas in the test piece.
For the testing process a vacuum is created inside the compensation tank, and the gas (preferably air) that is inside the tank is maintained at a temperature that corresponds essentially to the temperature of the interior wall of the test piece. The test piece, sealed at both ends, is inserted into the vacuum testing apparatus and connected to the compensation tank. Using isolating valves, at least one of the pipes in the circuit is closed off first. Subsequently, by means of the connected vacuum pump a vacuum that corresponds to the vacuum in the compensation tank is generated inside the test piece. During this time the connection between test piece and compensation tank remains closed at least on the one side in order to prevent any exchange of air from occurring. The air inside the test piece is then replaced with the temperature-controlled air from inside the compensation tank after a vacuum has been achieved in the test piece which substantially corresponds to the vacuum in the compensation tank. The colder air inside the test piece is transported into the compensation tank during this process, causing the warmer air that is present in the compensation tank to be displaced and transferred into the test piece. After the volume exchange has been completed, the connection between the test piece and the compensation tank is shut off once again. Now the temperature of the air inside the test piece corresponds in good approximation to the wall temperature, which is why a thermal equilibrium has now been achieved. The vacuum in the test piece is brought to match the measuring vacuum, and the progression of the vacuum level is monitored over a certain measuring period. If the vacuum losses exceed prescribed tolerance limits, the pipe is considered to be leaky and is separated from the rest.
After the examination is complete a new test piece is inserted into the vacuum testing apparatus; during this step the connection between the test piece and the equilibrium volume stays turned off. Only after this test piece has also been brought to match the vacuum are the two air volumes exchanged in accordance with the way described above.
It is advantageous to employ a heating device in order to keep the temperature of the air volume that is inside the compensation tank at the same temperature as the inside wall of the test piece. In this context it is also advantageous if a control unit triggers the heating device. This kind of adjustment utilizes the measured wall temperature as a command variable. Due to the fact that the thermal inertia precludes quick temperature changes in fixed-cycle tests it is sufficient if the temperature of the inside wall of the subsequent pipe, i.e. which is to be tested next, is used as that command variable. Also, it is advantageous to envision a heat-up circuit that can be shut off with a bypass valve and in which the air from the compensation tank circulates during the time it takes to exchange test pieces. The heating device is integrated into this circuit. The heat-up circuit is wired parallel to the test piece.
During the air exchange it is crucial that any mixing of air be suppressed; consequently, the air is introduced into the test piece and/or into the compensation tank essentially without vibration. According to a further development of the invention the air that is to be exchanged flows from the compensation tank into the test piece, in particular it enters the test piece in the area of the upper pipe crown. The flow exits in the area of the lower pipe crown. In the alternative, the transfer flow of air from the compensation tank into the test piece enters the latter as an essentially quasi-steady or turbulence-poor displacement flow. It is advantageous to envision these flows also with respect to the compensation tank.
Monitoring the progression over time of the vacuum ca
Burns Doane , Swecker, Mathis LLP
Cygan Michael
Josef Messman GmbH
Williams Hezron
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