What Is a Gas Manometer?

Gas pressure gauge An instrument for measuring gas pressure, or a differential pressure gauge that measures the pressure difference between two gases. The pressure here refers to the pressure per unit area, that is, the pressure, so it is also called a gas pressure gauge.

There are many types of instruments for pressure measurement. Commonly used are liquid pressure gauges, elastic pressure gauges and differential pressure gauges.

When selecting a pressure measuring instrument, it should be selected in consideration of the pressure of the measured medium, the nature of the measured medium, and the measurement requirements. On the premise of meeting the production requirements of the process, try to use instruments that are simple to use, easy to maintain, and inexpensive.

Select the type of pressure gauge

Select the type of pressure gauge according to the pressure of the measured medium, the display requirements for the pressure indication value, and the physical and chemical properties of the medium. For example, when measuring micro-pressure, it is obviously not possible to use a spring tube pressure gauge for measuring larger pressures, but only a tilt micro-pressure gauge or a capsule pressure gauge; if the pressure of the measured medium is not large and does not require rapid reading, U Pressure gauge or single tube pressure gauge; spring pressure is generally used for pressures above 49kPa; diaphragm pressure gauge can be used if the pressure of the measured medium is small and requires rapid reading.

If you need to observe the change of pressure, you should choose a recording type pressure gauge; if the pressure control requires an alarm, you can choose an electrical contact pressure gauge.

Select the measuring range of the meter

Starting from improving the accuracy of the instrument, it is hoped that the upper measurement limit of the selected instrument is close to the measured pressure. However, if the pressure of the measured medium exceeds the pressure, the pressure measuring elastic element will be damaged. Therefore, in order to ensure the reliability of the meter's work, it is usually used between 1/3 to 3/4 of the upper limit of the measurement for a calm measurement medium. In other words, the upper limit value of the selected instrument should be 1/4 greater than the maximum pressure of the measured medium. For the medium to be measured with large fluctuations, it should be used within the pressure range of the selected instrument upper scale 1/3 to 2/3.

Select the accuracy level of the meter

The accuracy of the pressure gauge is related to the type of instrument, which is mainly selected according to the tolerance requirements allowed in the process production. Generally speaking, when the accuracy is required, level l is used, and the others are level 1.5 to 2.5. ^[2]

Whether the installation of the pressure gauge is reasonable or not has a certain impact on the accuracy of the measurement, the service life of the instrument and the maintenance work. Therefore, sufficient attention must be paid to the installation of the pressure timer. The installation of the pressure gauge includes the installation of the pressure-receiving device, the pressure line and the instrument itself.

Installation of pressure taking device

(1) Selection of pressure taking point: The pressure taking point should truly reflect the pressure of the measured medium. It should be taken on the straight pipeline where the measured medium flows, but not in the sharp bends, valves, eddy currents, dead corners, etc. of the pipeline; the pressure taking point must meet the requirements of process production and be convenient for instrument personnel to maintain.

(2) Installation of pressure taking device: When measuring the pressure of gas, the pressure taking device is generally installed on the upper part of the horizontal pipe or inclined pipe to prevent the water in the gas from condensing into the duct, forming a water plug, and affecting the measurement accuracy.

Laying of impulse lines

The role of the impulse pipeline is to transfer the pressure of the measured medium from the pressure taking device to the pressure measuring instrument, and to ensure that no leakage occurs.

The impulse pipeline should be laid as short and straight as possible, with few elbows, and there should be no sharp bends or complex bends. The pipeline is too long or there are many elbows, which will increase the hysteresis of pressure transmission, and the longest is generally not more than 50m. ·

The impulse line needs to have a certain slope. When measuring the gas pressure, in order to avoid the accumulation of water in the line towel to affect the measurement accuracy, the impulse pipe should be tilted to the pressure taking device low, and the inclination is generally not less than 2%.

Installation of pressure instruments

In addition to the installation of the pressure gauge, its position should meet the environmental conditions (such as temperature, humidity, vibration, etc.) required by the gauge, and it should also pay attention to:

(1) The pressure gauge must be checked before installation, and it can be installed only after it is qualified.

(2) The installation place should be convenient for observation and maintenance. The installation height of ordinary pressure instruments is flush with the sight of ordinary people.

(3) The pressure gauge should be installed vertically.

(4) Consider the necessary protective measures. If the high-temperature gas pressure is measured, in order to prevent the pressure-sensing element from contacting the high-temperature gas, a U-shaped pipe or a coiled pipe should be added for buffering. If measuring the pressure of corrosive gas, an isolator should be installed. ^[3]