The second function that the restriction device provides is a pressure drop. This device is selected to provide the only significant pressure drop in the sample path.
RESTRICTOR KIT
The current revision of the 3000 series analyzers are supplied with a kit containing two restrictors and a union which are user installed. These parts supplied to give the end user more flexibility when installing the analyzer. The restrictor kit is suitable for high and low positive pressure applications as well as vacuum service ( atmospheric pressure sample) applications ( see manual for installation instructions). The standard restrictor ( BLUE DOT ) is recommended for pressures between 5 PSIG and 50 PSIG. For positive low pressure appli- cation ( 5 psig or less ) the un-marked restrictor is better suited . For none pressurized sample applications the marked restrictor should be used and configured for vacuum service. Note: for extremely low positive pressure appli- cations ( less then 2 psig) the vacuum service configuration should provide higher performance ( higher flow rates). For vacuum service the end user must supply a vacuum pump and a by-pass valve for the pump. A vacuum level of 5 -10 inches of mercury should provide the optimum flow rate. CAUTION: flow restrictors have very small orifices and may be plugged by small par- ticles ( .005” dia or larger) A sample filter must be included in the sample line prior to the restrictor! ( a 60 micron filter is recommended)
3020T EXAMPLES:
Example 1, with a incoming pressure of 10 psig the std restrictor (blue dot) will provide a flow rate of .76 SLPM. Up-stream of the restrictor the sample line pressure will be 10 psig, while down stream ( including the cell) the pressure will be at atmospheric pressure.( analyzer vented to atmospheric pressure) Note, all other pressure drops in the sample path are insignificant at these flow rates. This insures that the cell operates at atmospheric pressure. At very high flow rates ( off scale of flow-meter), pressure drops other than the restriction device could become significant , and result in pressurizing the cell.
Example 2, A 3020T is configured for vacuum service as follows. The un-marked restrictor is placed in the sample vent port. The down stream end of the restrictor is then connected to a vacuum pump and by-pass valve. The by- pass valve is adjusted to provide a flow rate of 1 SLPM. The sample pressure between the pump and the restrictor will be approximately -7 inches of mercury, while the pressure in the balance of the sample system including the cell will be approximately at atmospheric pressure. ( provided the sample flow into the analyzer is not blocked.)
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