All the problems with flange differential pressure level gauges?
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This post was last edited by Wang Tianze on 2015-12-11 at 19:38. For example, if a flanged differential pressure level gauge is to be used on a tank, two holes for the flanges need to be drilled; what should be the distance between these two holes? How tall is it? What is the range of the level gauge? Is it a positive migration or a negative migration? How are these number distances derived? Who can answer them one by one? Thank you
The hole spacing is a optimal value set according to the requirements of the manufacturing process, in order to ensure production capacity and meet the necessary production conditions; there is no uniform standard for it. The rest can be set accordingly; there’s nothing special about it. Normally, there is negative migration, and positive migration is not possible.
The opening size should be determined based on the production requirements of the process; the desired values can be obtained using the formula P=ρgh
The standard procedure is as follows: Lower edge: 150 mm above the headline. Upper level: 200 mm above the liquid level alarm or interlock value, and below the liquid feed inlet. If it is the liquid level of the tower (with a reboiler), it should be at the same level as the upper edge of the reboiler return pipe. If the negative terminal of the transmitter is connected to a liquid filling line or capillary tube, negative migration occurs; if the negative terminal is a \"pure gas phase line\" and the transmitter is installed below the outlet of the equipment, positive migration takes place. @jiaguoyun
The spacing between the openings is determined by the manufacturing process; no one at the manufacturer knows how high the liquid level in the tank should be； What does height refer to? The range needs to be calculated based on the specific medium in the storage tank; determine the density and use formulas to do the calculation. You can ask them to handle this during the design phase ； The magnitude of the migration, whether positive or negative, is determined based on the spacing between the openings and the density of the medium inside the tank.
As for the distance between the two holes, it is determined by the actual liquid level height; the measurement range is determined by the density of the medium being measured and the liquid level height – both of these values need to be calculated. As for whether to use a positive or negative offset, it depends on whether the installation height of the instrument is above or below the lowest liquid level relative to the horizontal line. If the instrument is installed at a height higher than the lowest liquid level, a positive offset is required; if it is installed at a lower height, a negative offset is needed
You can conduct a mechanical analysis of the transmitter being installed below the positive pressure side, between the positive and negative sides, or above the negative pressure side; through mathematical calculations, in all three cases the value obtained is the density ρ of the medium in the capillary, multiplied by the acceleration due to gravity g, and then by the distance H between the centers of the positive and negative flanges. The range of variation is given by ρ times g times H. In actual migration processes, the slight pressure exerted on the diaphragm box during the tightening of the flanges must also be taken into account (those with good manual skills can skip this step); the explanation here is rather vague