The core of the LPGFM1 flowmeter is a closed cylindrical shell. Shell installed inside a free rotation around the central axis of the cylindrical drum, the drum by the radial blade separated into three or four independent gas chamber (or ‘bucket’). Each chamber has straight slit openings in the inner wall (near the centre axis) and in the outer wall (near the housing): the inner opening serves as the inlet to the metering chamber of the chamber and the outer opening serves as the outlet of the chamber. The LPGFM1 housing is filled with about half the volume of water or low-viscosity oil as a sealing liquid, so that the lower half of the rotor is submerged in the liquid. This liquid sealing method is the key feature of the flowmeter, which replaces the mechanical sealing of the traditional volumetric flowmeter and achieves a unique leak-free operation.
gas from the flowmeter inlet into the workflow is as follows:
inflatable stage: the gas first into the current in a specific position of the gas chamber (such as A chamber). At this time, the A chamber of the inner inlet just exposed to the liquid surface, and the inlet connected to the gas began to fill the A chamber. At the same time, another chamber (e.g. chamber B) is filled with gas and its inner and outer openings are sealed by the liquid surface, forming a closed ‘bucket’ space - the metering chamber. A third chamber (e.g., chamber C) has its outer outlet exposed to the liquid surface and begins to vent gas to the meter outlet.
Drive and Rotation: As the gas continues to fill the A chamber, the rotating cylinder is subjected to an unbalanced force driven by the inlet pressure and begins to rotate counterclockwise around its central axis (direction of rotation depends on the design and is shown counterclockwise in the illustration).
At the same time, chamber A rotates to the original position of chamber B, and its inner and outer openings are sealed by the liquid surface, forming a new metering chamber. In this way, each chamber undergoes the cycle: inflation → formation of a sealed chamber → exhaust → reset by immersion.
Basis of Volumetric Measurement: The key point is that for each revolution of the drum, a volume of gas equal to ‘number of chambers × volume of individual chambers’ passes through the meter. For example, in the case of a four-chamber rotor, one revolution discharges four times the volume of the chambers. The number of rotations of the cylinder is transmitted to the external counting indicator (e.g. mechanical counter or electronic sensor) through the gearing mechanism, which can accurately add up the total volume of gas passing through the flowmeter.
LPG flowmeter by virtue of its liquid sealing principle, a unique class of non-leakage volumetric flowmeter. Its error characteristics (such as linearity, repeatability) and other rely on mechanical sealing of the volumetric flowmeter (such as girdle wheel, membrane) has a significant difference, usually with excellent accuracy, measurement accuracy of up to 0.2 level to 0.5 level. However, the principle of operation also brings specific limitations:
Flow Range Limitations: In order to ensure that the liquid can be effectively sealed in the gas chamber and the gas can be smoothly discharged without causing violent fluctuations in the liquid level or liquid entrainment, the rotating speed of the rotary cylinder can not be too fast. This directly limits the maximum measurable flow rate. Therefore, LPGFM1 flow meters are mainly suitable for accurate measurement of small flow gases, commonly used in laboratories, standard meter calibration, small flow monitoring of special processes and other scenarios.
Gas compatibility requirements: The gas to be measured must not be dissolved in the sealing liquid inside the flowmeter, nor can it have any chemical reaction or interaction with the sealing liquid. Failure to do so may result in measurement errors (e.g., small volume readings due to gas dissolution), changes in the nature of the liquid, or even damage to the meter. Selection of a suitable sealing liquid (water, oil or other inert liquid) is essential for accurate measurement of a particular gas.
Other considerations: The meter needs to be mounted horizontally and the liquid level needs to be maintained at the specified mark when in use. Changes in ambient temperature may result in changes in the volume of the sealing liquid and require attention or compensation. Whilst highly accurate, they are usually relatively large in size and weight and require regular maintenance of the level and cleanliness of the liquid.
In summary, LPG flowmeters, with their high accuracy, no leakage and intuitive principle, occupy an important position in the field of total volume measurement of small flow gases, but need to strictly follow their applicable flow ranges and gas-sealed liquid compatibility requirements.
