Inline Compressed Air Flow Meters

Characteristics of air flow measurement
① Large vibration. Not every air flow meter is installed in a place with high vibration. However, air flow meters installed in compression plants and blower rooms must consider vibration issues. This vibration comes mainly from compressors and blowers. The vibration of the machine can be transmitted far away through the air duct or air duct. Among them, the largest number of reciprocating compressors. The vibration generated during the operation of large reciprocating compressors often drives the plant to vibrate with the surrounding ground. Threats to the accurate and reliable operation of related air flow meters. It causes the fulcrum of the lever differential pressure transmitter to move and cause the indicator to drift. The vibration causes the vortex flow sensor to generate an interference signal corresponding to the vibration frequency, causing the flow indication value to be significantly higher.
② Gas carries water. Compressed air is taken from the atmosphere, which always contains a certain amount of water vapor. The content of water vapor is expressed by the partial pressure of water vapor ps. The saturated partial pressure of water vapor in the atmosphere is a function of atmospheric temperature. In rainy and foggy days, the partial pressure of water vapor in the outdoor atmosphere is saturated, that is, the relative humidity reaches 100%. Compressing the atmosphere at this time is like pressing a sponge that sucks up water. As the volume shrinks, a corresponding amount of water is precipitated. This is the simple principle that compressed air carries water. In fine weather, the relative humidity is low. But as it was compressed, the volume shrank to a fraction of its original size. The partial pressure of water vapor will increase accordingly, and it may enter into a saturated state and precipitate water droplets.
Large-diameter orifice plate flowmeter for measuring compressed air flow. There is often standing water in front of the orifice plate, which will affect the measurement accuracy. There is often a section of water in the impulse pipeline, which causes the differential pressure measured by the differential pressure transmitter to be inconsistent with the differential pressure generated by the throttling device. These are common causes of errors caused by water in the air. In addition, due to the high nitrogen oxide content in the urban atmosphere, water droplets contained in compressed air are acidic. Causes corrosion of the ring chamber surface and corrosion of the inner wall of the pipeline. Make it rough. When the iron oxide produced by corrosion becomes dry under certain conditions. It is easy to fall off the inner wall of the tube and be carried by the air flow in front of the orifice plate. This will also affect the flow indication. Therefore, during parking and maintenance, these powdery and lumpy garbage should be removed.
③ pulsating flow. Compressor and blower outlet fluids mostly contain certain pulsations. Reciprocating compressors, for example, appear as half-wave pulsations. Obvious fluctuations in the outlet pressure of the compressor and blower can be observed at the scene. Among them, the positive (fixed) displacement blower outlet pulsation frequency is relatively high, generally tens of hertz. And the reciprocating compressor outlet pulse frequency is relatively low, generally a few hertz. Flow arterial motion caused a variety of flowmeters such as differential pressure flowmeters, vortex flowmeters, etc. to show high values. Causes the float in the float flow meter to jump up and down. There are two commonly used methods to eliminate and reduce the effect of flow arterial motion on the flowmeter display value. One is to set a buffer tank at the compressor outlet to filter out the pulsation, and install the flow meter behind the buffer. In fact, the systems of reciprocating compressors are designed in this way. The second is to install the flow meter away from the source of the pulsation. In this way, the air volume of the process pipe and its pipe resistance can be used to form a low-pass filter attenuating the pulsation.