Device for sampling gas

A device for gas sampling for gas analysis is provided which uses detector tubes. The device includes a test gas container with a gas inlet pipe, a gas outlet pipe, a mounting opening for the detector tube and with a break-off device for a detector tube tip located in the mounting opening. Nonreturn valves are provided on the gas inlet pipe and the gas outlet pipe. The closing bodies of the nonreturn valves are pressed by springs against corresponding valve seats and are held in a closed position, and are arranged in relation to one another such that a sample gas flow can be established from the gas inlet pipe to the gas outlet pipe.

FIELD OF THE INVENTION
 The present invention pertains to a device for sampling gas for gas
 analysis by means of detector tubes.
 BACKGROUND OF THE INVENTION
 In a glass tube, detector tubes contain a chemical preparation that reacts
 with the substance to be detected while undergoing a change in color,
 while the conversion of the substance is quantitatively displayed in the
 form of a color length display. For sampling, the gas tube is first opened
 by breaking off the tips of the detector tube on both sides. The detector
 tube is then placed into a sampling pump in order to draw a predetermined
 volume of the test gas through the detector tube. A sampling pump, with
 which a gas sample can be delivered through a detector tube stroke by
 stroke, has been known from DE 38 22 001.
 However, the prior-art device for sampling gas cannot be used if very small
 amounts of substances that are also present in the ambient air atmosphere
 are to be detected. For example, a detector tube that is highly sensitive
 to water vapor must be used to detect water vapor in natural gas. If the
 tips of the detector tube are broken off only before the beginning of the
 measurement and the detector tube is placed into the sampling pump, the
 substance to be detected, which is present in the detector tube, is
 preloaded by the water vapor entering from the ambient atmosphere via the
 open tips of the detector tube such that measurement is no longer
 possible.
 SUMMARY AND OBJECTS OF THE INVENTION
 The primary object of the present invention is to improve a device of the
 above-described type such that gas analysis is possible without the
 influence of gas components from the ambient atmosphere.
 According to the invention a device for gas sampling for gas analysis using
 detector tubes is provided including a test gas container with a gas inlet
 pipe, a gas outlet pipe, a mounting opening for the detector tube and with
 a break-off device for a detector tube tip located in the mounting
 opening. Nonreturn valves are provided on the gas inlet pipe and the gas
 outlet pipe. The closing bodies of the nonreturn valves are pressed by
 springs against corresponding valve seats and are held in a closed
 position, and are arranged in relation to one another such that a sample
 gas flow can be established from the gas inlet pipe to the gas outlet
 pipe.
 The advantage of the present invention is essentially that by arranging the
 detector tube on a test gas container, through which sample gas flows, and
 by breaking off the tip of the detector tube under the atmosphere of the
 sample gas, effects of the ambient air on the substance to be detected are
 completely prevented from occurring. The gas sampling takes place such
 that the gas inlet pipe is connected to the gas source to be analyzed and
 the gas outlet pipe is connected to a gas delivery pump. The nonreturn
 valves located in the pipes open due to the vacuum applied by the gas
 delivery pump and the gas sample flows through the test gas container. The
 detector tube is then placed into the mounting opening located on the test
 gas container. The tip of the detector tube located within the mounting
 opening is removed by pressing the break-off device. The other end of the
 detector tube is then connected to a sampling pump, and the second tip of
 the detector tube is then opened, e.g., with another break-off device
 located on the sampling pump. The sample volume corresponding to the
 detector tube can now be drawn through the detector tube.
 The gas sampling may be performed either with or without flow through the
 test gas container, and a site-independent measurement is also possible in
 the case of a test gas container with flow through, because the nonreturn
 valves close after interruption of the suction process or after the test
 gas container has been uncoupled from the sampling source and the gas
 delivery pump, so that no gas can penetrate into the interior space of the
 test gas container from the outside.
 The spring force acting on the closing body of the nonreturn valve at the
 gas inlet pipe is advantageously selected to be such that it is stronger
 than the maximum suction force that can be applied by the sampling pump.
 It is achieved as a result that no foreign gas can be drawn into the test
 gas container from the environment by means of the sampling pump in the
 case of a site-independent measurement. A sampling pump with a detector
 tube has been known from U.S. Pat. No. 4,947,696 which is hereby
 incorporated by reference.
 With a test gas container of a specifically defined volume, e.g., 100 mL,
 the sample volume can be limited to less than 100 mL. In the case of
 measurement at the test gas container with the valves closed, sample is
 taken only until the vacuums in the test gas container and in the sampling
 pump become equal. As a result, it is possible to use even smaller sample
 volumes for the measurement of very high pollutant concentrations.
 One exemplary embodiment of the present invention is shown in the figure
 and will be explained in greater detail below.
 The various features of novelty which characterize the invention are
 pointed out with particularity in the claims annexed to and forming a part
 of this disclosure. For a better understanding of the invention, its
 operating advantages and specific objects attained by its uses, reference
 is made to the accompanying drawing and descriptive matter in which a
 preferred embodiment of the invention is illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring to the drawing in particular, the FIGURE schematically shows a
 test gas container 1 with a gas inlet pipe 2, a gas outlet pipe 3, a
 mounting opening 4 for the detector tube 5, and a break-off device 6 for
 the tip 7 of the detector tube. The other end of the detector tube 5 is
 connected via a flexible tube 8 to a sampling pump 9, whose grip plates 10
 can be pressed together for sampling gas.
 Nonreturn valves 11, 12, whose closing bodies 13, 14 are pressed by means
 of springs 15,16 against the corresponding valve seats 17, 18, are located
 in the pipes 2, 3. The nonreturn valves 11, 12 are arranged within the
 pipes 2, 3 such that only a sample gas flow is possible from the gas inlet
 2 to the gas outlet 3.
 The gas inlet 2 is connected to a sampling source 19, e.g., a natural gas
 source, while the gas outlet pipe 3 is connected to a gas delivery pump
 20.
 Water vapor in natural gas is to be detected with the device according to
 the present invention, e.g., during gas sampling on a drilling rig.
 The measurement takes place such that the gas delivery pump 20 is first
 switched on and natural gas is drawn in from the sampling source 19. After
 sufficient scavenging of the test gas container 1, the unopened detector
 tube 5 is placed with one side into the mounting opening 4, while the
 other side is connected to the sampling pump 10 via a flexible tube 8. The
 tips of the detector tube are subsequently removed by means of the
 break-off device 6 and by pressure on the flexible tube 8. The gas
 sampling can now be carried out by pressure on the grip plates 10
 according to the measuring instructions of the detector tube 5.
 In the case of site-independent gas analysis, the sampling source 19 and
 the gas delivery pump 20 are separated from the test gas container, and
 the nonreturn valves 11, 12 will close automatically. Site-independent
 measurement may be necessary when the gas sampling can be carried out
 under difficult conditions only and no detector tube 5 can be used for the
 gas analysis on the site.
 While a specific embodiment of the invention has been shown and described
 in detail to illustrate the application of the principles of the
 invention, it will be understood that the invention may be embodied
 otherwise without departing from such principles.