About gas chromatograph gas circuit failure and troubleshooting
November 11 10:18:12, 2020
1. Flow adjustment 1. The flow cannot be adjusted (1) Visual inspection: first check whether there is any obvious air leakage in the instrument system. When a large leak occurs in the gas path of the instrument system, it is likely that the flow rate cannot be adjusted up. If you can't hear the leak, go to (3). (2) Leak detection: After hearing the air leakage, you can gradually locate according to the direction of the sound. At this time, the application of soap liquid can be used to further determine the occurrence of air leakage. After finding the cause, plug the leak in time. (3) Observation of pre-column pressure: Observe the value of the pre-column pressure indicator to quickly determine whether it is a fault caused by the gas source or a blockage and damage caused by the internal gas path of the instrument. If the pre-column pressure is too low (precisely lower than the predetermined pressure during normal flow operation), the gas source needs to be checked; if the pre-column pressure is normal, the internal gas path of the instrument needs to be checked. (4) High-pressure inspection of steel cylinder: After opening the cylinder valve, observe the indication of the high-pressure gauge, and the pressure should be between 1 ~ 15MPa. If the pressure is below 1MPa, stop the cylinder and change the air; if the pressure value is within the appropriate range, it means that the cylinder pressure is normal. (5) Check the output of low pressure on the pressure reducing valve: adjust the pressure reducing valve to see if the low pressure meter on the cylinder can be adjusted to between 0.25 ~ 0.6MPa. If it is normal, it is suspected that there is a blockage in the gas line filter joint or that there is a problem with the stability valve on the instrument. At this time, it should be carried out according to (6); if the low pressure value is abnormal, it means that there is a problem with the pressure reducing valve and needs to be carried out (7) Repair. (6) The filter is clogged and the pressure regulator valve is checked: the joint from the outlet of the filter to the inlet of the air source of the instrument is slowly unscrewed, and observe whether there is a strong air flow running out of the joint. If there is, it means that the filter is not blocked, and the regulator valve may be defective. After confirming that the regulator valve is not out of gas, the valve can be disassembled and cleaned, which may be caused by the clogging between the valve needle and the valve seat in the regulator valve. If the valve still does not work properly after cleaning, it is better to replace it with a new valve; if there is no strong air flow from the unscrewed joint in the above test, you need to check the possible clogging before and after the filter inlet; of course, the middle pipeline is also blocked Possible, but the incidence is very small. (7) Pressure relief valve repair: After the structure of the pressure relief valve is understood, the pressure relief valve can be removed and repaired. Because there is high pressure on the inlet side of the pressure reducing valve, it is best not to disassemble blindly without repair experience. If possible, it is recommended to replace with a new valve; when replacing the valve, it must be noted that the hydrogen or oxygen meter should be used separately from the pressure reducing valve used in other gas source tables, and the dedicated gas source name should be marked on the pressure reducing valve. (8) Deactivation, ventilation: When the pressure of the cylinder is too small, it should be immediately deactivated, replaced with a new cylinder or inflated. Under too small pressure, not only the output of the gas source is unstable, but also the impurity concentration in the gas source will increase significantly, which is particularly disadvantageous for high-sensitivity analysis. Another issue that must be noted is that the residual gas in the steel cylinder, especially the residual gas in the hydrogen cylinder, cannot be discharged casually. (9) Remove the column inlet gas path: Remove the gas joint at the column inlet and observe whether the rotor in the flowmeter can rise to the uppermost end. If it can rise to the uppermost end, it means that the gas path in front of the column is normal, and go to (10) for further inspection; if the rotor does not reach the uppermost end, it means that the gas path in front of the column is blocked, and (13) check is needed. (10) Remove the column outlet: After connecting the column inlet back to the original gas path, remove the column outlet side connector, and then observe whether the rotor in the flowmeter can be adjusted to a predetermined value. If it is possible, it will be judged that the pipeline and detector behind the column are clogged, and it needs to be handled according to (11); if the rotor is still not adjusted, the column is considered to be too tightly packed, and it needs to be carried out according to (12). (11) Blockage inspection and elimination: queues and cleaning should be performed when it is judged that the pipeline or detector behind the column is blocked. (12) The column packing is too tight: the main reason for the column packing is too tight is that the carrier mesh is too large, which is caused by excessive air resistance. After appropriately using a carrier with a smaller mesh size or reducing the length of the chromatographic column, the flow rate can be adjusted up to a predetermined value. (13) Remove the outlet gas connector of the flowmeter: after unwinding the gas path at the outlet end of the rotor flowmeter, observe whether the rotor can rise to the highest end. If it is possible, it is judged that the sampling and the gas path of the carburetor are clogged, and processed according to (14); if the rotor still cannot rise to the highest end, it may be considered that the flow valve is damaged or the inlet pipeline of the flow meter is blocked, and then press (15). (14) Blocking of the inlet: The blockage of the injector can be carried out according to the cleaning procedure of the syringe. (15) Blockage of flow valve and pipeline: A block test will quickly determine whether the flow pipeline is blocked. If there is, clean the gas pipeline; if the pipeline in front of the flowmeter is normal, the flow control valve can be removed for cleaning. 2. The flow rate is too large and not small. If the gas flow rate is always too large to be adjusted down, it can be regarded as a malfunction of the gas circuit control system. There are three reasons for this type of failure: first, there is a leak in the gas path behind the flowmeter; second, the gas resistance of the gas path is too small; third, the flow control valve is damaged. The inspection method is as follows: first block the gas outlet of the detector, and observe whether the rotor in the flowmeter can be lowered to zero. If it cannot be reduced to zero, it is necessary to consider the inspection of the air leakage. For the specific method, see the inspection and elimination of air leakage; if the rotor can be reduced to zero, it means that the system does not leak. At this time, it should be observed whether there is a large change in the flow rate when the flow regulating valve rotates. If there is a change, the air resistance of the gas path can be increased appropriately; if there is no change, the valve itself should be suspected to be problematic. The treated valve should be reinstalled in the original gas circuit for control test. For more information, please download the document. For more information about the gas chromatograph, please visit the booth of Shanghai Guige Industry Co., Ltd. >>> http: //
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