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I. The requirements for installing pressure guiding tubes when using differential pressure flow meters are as follows. (1) The pressure lead should be laid over the shortest possible distance; under normal circumstances its total length should be greater than 50 m to avoid excessive resistance and response lag ； But not less than 3m. Because it indicates frequent fluctuations in situations where flow rates change too rapidly, this can cause the differential pressure gauge to reach excessive temperatures when dealing with high-temperature media. The bends in the pipeline should have uniform rounded corners. (2) Measures should be taken to eliminate other components that may accumulate in the pressure tap conduit, such as gas, moisture, liquids, or solid particles, which can affect the accurate and reliable transmission of the pressure difference. To this end, the pressure guiding catheter should be installed at an inclination of not less than 1:10 between the vertical and horizontal planes, and collectors and settlers for gases, condensates, and particles should be installed for regular discharge. (3) The pressure lead should be free from the influence of external heat sources, and a heating element should be provided to prevent freezing. (4) For viscous and corrosive media, to prevent clogging and corrosion, an isolation tank filled with isolation fluid should be installed. (5) All pressure lead pipes must be sealed to prevent any leakage. (6) The pressure lead piping shall be equipped with the necessary valves for shutdown, flushing, filling with sealant, and waste discharge. II. Common faults, causes, and troubleshooting methods for differential pressure flow meters. 1. The indication is zero or the movement is very small. The reasons are: (1) The balance valves are not fully closed or are leaking ； (2) The high and low pressure valves at the root of the throttling device are not open ； (3) Blockage of valves and pipelines between the throttling device and the differential pressure gauge ； (4) The vapor pressure conduit has not been fully condensed ； (5) The gasket between the throttling device and the process pipeline is not tight enough ； (6) Internal failure of the differential pressure gauge. The corresponding treatment method is: (1) Close the balance valve, and repair or replace it ； (2) Open ； (3) Flush the pipeline, repair or replace the valve ； (4) Start the meter after complete condensation ； (5) Tighten the bolts or replace the gasket ； (6) Inspection and repair. 2. The indicator is below zero. The reasons are: (1) Reverse connection of high and low pressure pipelines ； (2) Reverse connection of signal lines ； (3) Severe leakage or rupture in the high-pressure side pipeline. The corresponding handling method is: (1) Check and connect properly ； (2) Check and connect properly ； (3) Replace the part or the pipe. 3. The indication is low. The reasons are: (1) The high-pressure side pipeline is not airtight ； (2) The balance valve is not tight or not properly closed ； (3) Air not fully exhausted from the high-pressure side pipeline ； (4) Zero drift or displacement of the differential pressure gauge or secondary instrument ； (5) The throttle device and differential pressure gauge are not matched, failing to meet the design specifications. The corresponding handling method is: (1) Check and eliminate leaks ； (2) Inspect, shut down, or repair ； (3) Drain the air ； (4 Inspection, adjustment ； (5) Replace the accompanying differential pressure gauge as specified in the design. 4. The indication is high. The reasons are: (1) The pipeline on the low-pressure side is not airtight ； (2) Air accumulation in the low-pressure side pipeline ； (3) The pressure of steam, etc., is below the design value ； (4) Differential pressure gauge zero drift ； (5) The throttle device and differential pressure gauge are not matched, failing to meet the design specifications. The corresponding handling method is: (1) Check and eliminate leaks ； (2) Drain the air ； (3) Adjust according to the actual density ； (4) Inspection and adjustment ； (5) Replace the accompanying differential pressure gauge as specified. 5. The indication exceeds the upper limit of the scale. The reasons are: (1) The actual flow rate exceeds the design value ； (2) Severe leakage in the low-pressure side pipeline ； (3) There is a broken wire in the signal line. The corresponding treatment method is: (1) Replace it with a differential pressure gauge within the appropriate range ； (2) Eliminate leakage ； (3) Inspect and repair. 6. The indication changes slowly when the flow rate changes. The reasons are: (1) The connection pipes and valves are blocked ； (2) There is a fault inside the differential pressure gauge. The corresponding treatment methods are: (1) Flush the pipelines and clear the valves ； (2) Check and rule out. 7. The indication fluctuates greatly. The reasons are: (1) The flow rate parameters themselves fluctuate too much ； (2) The pressure sensing element is sensitive to parameter fluctuations. The corresponding handling method is: (1) Slightly reduce the opening of the high and low pressure valves ； (2) Appropriately adjust the damping effect. 8. Indicate no movement. The reasons are: (1) The anti-freezing system failed, causing the hydraulic fluid in the differential pressure gauge and pressure conduits to freeze ； (2) The high and low pressure valves are not open. The corresponding treatment methods are: (1) enhancing the effectiveness of anti-freezing facilities ； (2) Open the high and low pressure valves. III. Under what circumstances is it necessary to install a condenser, gas collector, settler, and isolator on a differential pressure flow meter? When the liquid in the pressure guiding tube cools down due to the ambient temperature, or when its conditions differ from those in the measurement pipeline – for example, when measuring steam flow – a condenser should be installed in the differential pressure pipeline. The condensation surfaces in the positive and negative pressure tubes should be at the same height and remain constant; this way, no measurement errors will occur when there are sudden changes in differential pressure. When the medium being measured is a liquid, gas collectors and exhaust valves should be installed at the highest points of the pressure guiding tubes, in order to collect and regularly discharge various gases that form within the liquid. When measuring liquids containing impurities and the flow rate of humid gases, a sediment trap and a drain valve should be installed at the lowest point of the conduit to collect and regularly remove various contaminants and accumulated water from within the signal tube. When measuring fluids that are corrosive, highly viscous, prone to condensation, or capable of precipitating solids, isolators and isolation fluids should be used to separate the fluid under measurement from the conduits of the differential pressure instrument.