Measuring and testing – Gas content of a liquid or a solid
Reexamination Certificate
2000-01-11
2002-05-28
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas content of a liquid or a solid
C073S019050, C073S019100
Reexamination Certificate
active
06393893
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a measuring apparatus for measuring the gas loading of a liquid, particularly of a liquid plastics component, comprising a pump which is disposed in a circuit for the sample quantity and the pump piston of which can be adjusted, with displacement control and by means of an actuating drive, in both directions of travel in the measuring cylinder chamber, comprising a switchable valve device forming a filling and ejection valve for filling the measuring cylinder chamber with the sample quantity to be measured and for carrying away the sample quantity from the measuring cylinder chamber after the measuring operation has been performed, and comprising a pressure measuring device which is associated with the measuring cylinder chamber and with which the pressure of the sample quantity, which is isolated in the measuring cylinder chamber when the valve device is closed, can be measured at different predetermined positions of displacement of the pump piston in order to determine the gas loading. The present invention is further oriented towards a method of determining the gas loading of a liquid, using the measuring apparatus according to the invention in particular.
BACKGROUND OF THE INVENTION
In technology, and above all in plastics processing technology, it is frequently necessary to measure the gas loading of liquids, e.g. the content of air of liquid plastics components for the production of foamed materials, generally with the aim of being able to operate with a constant gas loading in continuous operation.
Numerous measuring apparatuses have long been known for determining the gas loading of liquids, particularly of liquid plastics components (DE 37 20 904 A1, DE 33 36 037 A1, DE 31 32 597 C2, DE 36 30 209 A1, DE 41 19 966 A1, EP 0 125 541 A2). These known measuring apparatuses generally employ measuring cylinders which are provided with measuring pistons and into which a defined amount of sample is drawn off at intervals from the system conveying the gas-laden liquid. A measurement is then made on this sample, which is isolated from the system in the measuring cylinder. This is generally effected by subjecting the sample quantity, which is loaded with dissolved gas and possibly with free gas also, to a reduced pressure in the closed measuring cylinder chamber, with the release of the gas, by increasing the volume of the measuring cylinder chamber by correspondingly adjusting the piston. The gas loading of the liquid can be calculated from the changes in volume determined and from the changes in pressure of the sample quantity in accordance with known physical relationships (gas law). It is possible to achieve the same result if the measuring sample is measured in the measuring cylinder by compression by means of the measuring piston and/or by a combination of decompression and subsequent compression, with the measurement of pressure under the different test conditions and simultaneous determination of the volume of the measuring space for the different piston positions.
A measuring apparatus for measuring the gas loading of a liquid, particularly a liquid plastics component, comprising a pump which is disposed in a circuit for the sample quantity and the pump piston of which can be adjusted, with displacement control and by means of an actuating drive, in both directions of travel in the measuring cylinder chamber, comprising a switchable valve device forming a filling and ejection valve for filling the measuring cylinder chamber with the sample quantity to be measured and for carrying away the sample quantity from the measuring cylinder chamber after the measuring operation has been performed, and comprising a pressure measuring device which is associated with the measuring cylinder chamber and with which the pressure of the sample quantity, which is isolated in the measuring cylinder chamber when the valve device is closed, can be measured at different predetermined positions of displacement of the pump piston in order to determine the gas loading is known from U.S. Pat. No. 4,376,172. The measuring cylinder chamber of which is connected on its inlet side, via a filling valve, to the system which carries the gas-laden liquid under pressure and which comprises a supply vessel for the gas-laden liquid, and which is connected on its outlet side, via an ejection valve, to a return line which leads back to the supply vessel. Here also, the gas loading is measured by withdrawing a defined amount of sample from the system and feeding it to the measuring cylinder of the measuring pump, followed by making a measurement on the sample with the filling and ejection valves closed, namely with the sample isolated from the system, for which purpose firstly a reduced pressure and then an overpressure is generated in the measuring cylinder by adjusting the piston with control of the displacement thereof. In the course of this procedure, the measured pressure values, as well as the changes in volume of the measuring cylinder chamber which result from the displacement movements of the measuring piston, are processed by an electronic evaluation unit and are utilized for controlling the gas loading of the liquid at a predetermined constant value. After the measuring operation has been performed, the filling valve and the outlet valve are opened again, so that the test sample is returned to the supply vessel again by the pump pressure in the system. In the intervals between the periodic measurements made on samples, the measuring cylinder of the pump is always connected to the pumping system of the installation as a whole.
SUMMARY OF THE INVENTION
This invention stems from these known measuring apparatuses, and stems in particular from the apparatus which employs measuring pump according to the aforementioned U.S. Pat. No. 4,376,172. The object of the invention is primarily to fashion this system, particularly the piston pump which is used here as the measuring apparatus for gas loading, without an excessive cost of construction and so that an accurate measurement of the gas loading of liquids, particularly of liquid plastics components for the production of synthetic foam, can be achieved in different operating systems and with different arrangements of the piston pump.
This object is achieved according to the invention by providing the actuating drive of the piston pump as a controlled servomotor together with a transmission gear and by constructing the piston pump at the same time as a feed pump which returns the test sample from the measuring cylinder chamber to the system after the measuring operation has been performed.
With this design of measuring apparatus, and by means of the controlled servomotor and of the associated transmission gear, it is possible to make a very accurate adjustment of the displacement of the pump piston both in the direction of suction and in the direction of compression, and it is consequently possible to make an accurate determination of the change in volume of the measuring cylinder chamber which occurs during the measuring operation, so that the gas content of the test sample can be determined exactly via the displacement-dependent changes in volume and via the pressure values which are measured simultaneously. At the same time, the piston pump according to the invention can operate as a feed pump which pushes the test sample out of the pump cylinder forming the measuring cylinder chamber when the ejection valve is opened after the measurement has been made. Thus,it is also possible to locate the piston pump according to the invention in a separate circuit which is separated from the pumping system of the installation as a whole, and to shut off the measuring cylinder chamber of the piston pump from the pressurised system in the intervals between measuring operations. In this connection, valves which can be switched independently of each other from their closed position into their open position and vice versa are preferably used for the filling valve and the ejection valve which are associated with the piston pu
Fetz Dietmar
Hausbichler Hannes
EDF Polymer Applikation Maschinenfabrik GmbH
Larkin Daniel S.
Vickers Daniels & Young
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