The measurement of the gas pressure in the ventilation pipe shall be carried out in the pipe section with relatively stable air flow. During the test, the static pressure, dynamic pressure and total pressure of the gas shall be measured. The orifice for measuring the total gas pressure shall face the direction of the air flow in the air duct, and the orifice for measuring the static pressure shall be perpendicular to the direction of the air flow.

用U形压力计测全压和静压时，另一端应与大气相通(用倾斜微压计在正压管段测压时，管的一端应与大气相通，在负压管段测压时，容器开口端应与大气相通)。因此压力计上读出的压力，实际上是风道内气体压力与大气压力之间的压差(即气体相对压力)。大气压力一般用大气压力表测定。由于全压等于动压与静压的代数和，可只测其中两个值，另一值通过计算求得。

When the U-shaped pressure gauge is used to measure the total pressure and static pressure, the other end shall be connected with the atmosphere (when the inclined micro pressure gauge is used to measure the pressure in the positive pressure pipe section, one end of the pipe shall be connected with the atmosphere, and when the pressure is measured in the negative pressure pipe section, the open end of the container shall be connected with the atmosphere). Therefore, the pressure read out 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 pressure of the gas). 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.

山东通风管道

Shandong ventilation duct

测定仪器

Measuring instrument

气体压力(静压、动压和全压)的测量通常是用插入风道中的测压管将压力信号取出，在与之连接的压力计上读出，常用的仪器有毕托管和压力计。

The measurement of gas pressure (static pressure, dynamic pressure and total pressure) is usually to take out the pressure signal with the pressure measuring pipe inserted into the air duct and read it on the pressure gauge connected to it. The commonly used instruments are pitot tube and pressure gauge.

1毕托管

1 pitot tube

(1)标准毕托管

(1) Standard pitot tube

它是一个弯成90°的双层同心圆管，其开口端同内管相通，用来测定全压;在靠近管头的外壁上开有一圈小孔，用来测定静压，按标准尺寸加工的毕托管校正系数近似等于1。标准毕托管测孔很小，通风管道内易被粉尘堵塞，因此这种毕托管只适用于比较清洁的管道中测定。

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 small hole is opened on the outer wall near the pipe head to measure the static pressure. The pitot tube correction coefficient processed according to the standard size is approximately equal to 1. The standard pitot tube measuring hole is very small, and the ventilation pipe is easy to be blocked by dust. Therefore, this pitot tube is only suitable for measuring in relatively clean pipes.

(2)S型毕托管

(2) S-type pitot tube

它是由两根相同的金属管并联组成，测量时有方向相反的两个开口，测定时，面向气流的开口测得的相当于全压，背向气流的开口测得的相当于静压。由于测头对气流的影响，测得的压力与实际值有较大误差，特别是静压。因此，S型毕托管在使用前须用标准毕托管进行校正，S型毕托管的动压校正系数一般在0.82～0.85之间。S型毕托管测孔较大，通风管道内不易被粉尘堵塞，这种毕托管在含尘污染源监测中得到广泛应用。

It is composed of two identical metal tubes in parallel. During measurement, there are two openings in opposite directions. During measurement, the opening facing the air flow is equivalent to total pressure, and the opening facing the air flow is equivalent to static pressure. Due to the influence of the probe on the air flow, there is a large error between the measured pressure and the actual value, especially the static pressure. Therefore, the S-type pitot tube must be corrected with standard pitot tube before use. The dynamic pressure correction coefficient of S-type pitot tube is generally between 0.82 and 0.85. The measuring hole of S-type pitot tube is large and it is not easy to be blocked by dust in the ventilation pipe. This pitot tube is widely used in the monitoring of dust pollution sources.