The use of compressed air flow meters must avoid the following disadvantages.1. Great vibration. Not every air flow meter is installed in places with high vibration. However, the air flow meters installed in the compression plant and the blower room have to consider the vibration problem. This kind of vibration mainly comes from compressors and blowers. The vibration of the machine can be transmitted to far places through air ducts or ducts. Among them, the largest vibration is the reciprocating compressor. The vibration generated during the operation of the large reciprocating compressor often drives the workshop and the surrounding ground to vibrate together, posing a threat to the accurate and reliable operation of the relevant air flowmeter. It causes the fulcrum of the lever-type differential pressure transmitter to move and causes the meter to drift in indication. Vibration causes the vortex flow sensor to produce an interference signal corresponding to the vibration frequency, causing the flow indication to be significantly higher. Two, the gas carries water. The compressed air flowmeter is taken from the atmosphere, and the atmosphere always contains a certain amount of water vapor. The content of water vapor is expressed by the partial pressure of water vapor ps. The partial pressure of water vapor saturation in the atmosphere is a function of atmospheric temperature. In rainy and foggy days, the partial pressure of water vapor in the outdoor atmosphere reaches saturation, that is, the relative humidity reaches 100%. At this time, compressing the atmosphere is like compressing a sponge that absorbs enough water. As the volume shrinks, there is a corresponding amount Water precipitates out. This is the simple principle of compressed air with water. In fine weather, the relative humidity of the atmosphere is low, but as it is compressed and reduced to a fraction of its original volume, the partial pressure of water vapor will increase accordingly, and it may also enter a saturated state and precipitate water droplets.Large-caliber orifice flowmeters used to measure the flow of compressed air often have water in front of the orifice, which will affect the accuracy of the measurement. 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 produced 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, the water droplets contained in the compressed air are acidic, causing corrosion on the surface of the annular chamber, corrosion of the inner wall of the pipeline, and roughening of the surface. When the iron oxide produced by corrosion becomes dry under certain conditions, it is easy to fall off from the inner wall of the pipe and be carried by the airflow to the front of the orifice plate, which will also affect the flow rate indication. Therefore, these powdery and lumpy garbage should be removed when parking for maintenance.3. Pulsating flow. Most of the outlet fluids of compressors and blowers contain certain pulsation. For example, a reciprocating compressor exhibits half-wave pulsation. It can be observed that the outlet pressure of the compressor and the blower fluctuates significantly at the scene. Among them, the outlet pulsation frequency of the positive (fixed) displacement blower is relatively high, generally tens of Hz, while the outlet pulsation frequency of the reciprocating compressor is relatively low, generally a few Hz. The flow arterial movement causes the differential pressure flowmeter, vortex flowmeter and other flowmeters to show high values, causing the float in the float flowmeter to jump up and down. There are two common methods to eliminate and weaken the influence of flow arterial movement on the value of the flowmeter. One is to install a buffer tank at the compressor outlet to filter out the pulsation, and install the flowmeter behind the buffer. In fact, the reciprocating compressor system is designed in this way; the second is to install the flowmeter away from the source of pulsation, so that the gas capacity of the process pipeline and its pipe resistance can be used to form a low-pass filter to attenuate the pulsation.
Post time: 21-09-21