The measurement of gas pressure in Jinan ventilation pipe should be carried out in the pipe section with stable air flow. The static pressure, dynamic pressure and total pressure of the gas should be measured in the test. The orifice for measuring the total pressure of the gas should face the direction of the air flow in the air duct, and the orifice for measuring the static pressure should be perpendicular to the direction of the air flow.
When U-shaped manometer is used to measure the total pressure and static pressure, the other end should be connected with the atmosphere (when inclining micro manometer is used to measure the pressure in positive pressure pipe section, one end of the pipe should be connected with the atmosphere; when measuring the pressure in negative pressure pipe section, the open end of the container should be connected with the atmosphere). Therefore, the pressure read on the pressure gauge is actually the pressure difference between the gas pressure in the air duct and the atmospheric pressure (i.e. the relative gas pressure). Atmospheric pressure is generally measured with an atmospheric pressure gauge. Since the total pressure is equal to the algebraic sum of dynamic pressure and static pressure, only two values can be measured, and the other value can be obtained by calculation.
Jinan ventilation pipe
Gas pressure (static pressure, dynamic pressure and total pressure) is usually measured by taking out the pressure signal from the pressure measuring tube inserted into the air duct and reading it on the pressure gauge connected with it. The commonly used instruments are pitot tube and pressure gauge.
(1) Standard pitot
It is a double-layer concentric tube bent into 90 ° and its open end is connected with the inner tube to measure the total pressure; a circle of small holes are opened on the outer wall near the tube head to measure the static pressure, and the pitot tube correction coefficient processed according to the standard size is approximately equal to 1. The measuring hole of standard pitot tube is very small, and it is easy to be blocked by dust in Jinan ventilation pipe. Therefore, this kind of pitot tube is only suitable for measuring in relatively clean pipe.
(2) S-type pitot tube
It is composed of two identical metal tubes in parallel. When measuring, there are two openings in opposite directions. When measuring, the opening facing the air flow is equivalent to the total pressure, and the opening facing the air flow is equivalent to the static pressure. Due to the influence of the probe on the air flow, there is a big error between the measured pressure and the actual value, especially the static pressure. Therefore, S-type pitot tube must be calibrated with standard pitot tube before use, and the dynamic pressure correction coefficient of S-type pitot tube is generally between 0.82 and 0.85. The S-type pitot tube has a large measuring hole, and it is not easy to be blocked by dust in Jinan ventilation pipeline. This kind of pitot tube is widely used in the monitoring of dust pollution sources.