The basis of any direct reading Dräger-Tube is the chemical reaction of the measured substance with the chemicals of the filling preparation. Since this reaction leads to a discoloration, the Dräger-Tubes can also be called colorimetric chemical sensors. The substance conversion in the Dräger-Tube is proportional to the mass of the reacting gas.
The Dräger-Tube measurement system consists of a Dräger-Tube and a Dräger-Tube pump. Each Dräger-Tube contains a very sensitive reagent system that produces accurate readings when the technical characteristics of the gas detector pump precisely match the reaction kinetics of the reagent system in the tube. Therefore, a gas detector pump, delivering the correct volume must also pull the sample through the Dräger-Tube at the proper rate.
The Dräger-Tube pump is a bellows pump. It can easily be perated with one hand and draws in 100 ml per stroke. When measuring, the pump body (bellows) is pressed together completely. This corresponds to one "stroke". During the stroke the air contained in the pump chamber escapes through the exhaust valve. The suction process runs automatically after the bellows are set free. The exhaust valve is closed during the opening phase of the bellows so that the gas sample flows through the connected Dräger- Tube into the pump. After the complete opening of the pump body into its original position the suction process is finished. The end of stroke is visible by a pressure-controlled end of stroke indication, located in the pump head. An internal scissor mechanism built into the
Dräger pump bellows provides parallel compression of the pump and an automatic stroke counter which is integrated in the pump head records the number of strokes.
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