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SF-1 Pressure Difference Moisture Determination Device

Determination of trace moisture in plastic particle includes pressure difference method, electrolysis method, Karl Fisher method etc. Among which, the moisture determination by differential pressure, with its advantages in rapidness, accuracy, operational convenience, and low operational costs, etc, has been widely applied during the intermediate processes in chemical fiber and plastic industries, especially for measuring the trace moisture contents in the particles such as polyester chips, nylon 6, nylon 66 chips, etc, which directly and considerably affect the quality of filatures prior to being molten and after being dried. This method is also applicable to measure the general trace moistures in the particles such as nylon 6, nylon 66, etc and plastic resins.

The determination device of moisture by the pressure difference method may be applied to measure extremely trace moistures bonded with the internal molecular structures of raw materials; but they may not be applied to measure the moistures balanced between raw materials and environments. When materials are heated up and molten with internally contained moistures, they may be degraded and their feature viscosity may be decreased, and product quality may be directly affected. It is generally required that prior to making filatures, the moisture ratio must be less than 0.03%; therefore, after raw materials are dried and before they are made into filatures, the pressure difference method must be applied to measure their internal extremely low moisture ratios. The moisture ratio in vacuum-packed plastics may also be measured by applying the pressure difference method.

This device can measure 1.5mg in water content at highest.

When test samples contain higher contents of the volatilizing mixtures other than water, the reliability of testing results must be considered.


The test device shown in figure 1 is an air tightness system composed of one glass pipeline, one cuvette, and glass bulbs A and B. The U-shaped pipeline L holds a certain amount of silicon oil. Achieve a high degree of system vacuum when the air valve G is open; if the entire system is good in air
tightness, the air pressures at D and E liquid levels at both sides of the silicon oil must be the same when close the air valve G, and the liquid levels of the silicon oil at both sides must be at the same horizontal level. If the air pressure at the right side rises up due to some reasons, then the pressure D at the right liquid level will rise up, the liquid level of the silicon oil will rise up or lower down accordingly, the right liquid level will lower, and the left liquid level will rise. If some watercontaining substances are put into the cuvette in advance and such moisture may be released only under certain (such as heated) conditions, then when the conditions are not ready for moisture release, D and E liquid level pressures equal to each other; when such conditions are ready, the pressure inside the right system pipeline will rise up due to effects of the water vapors; D liquid level pressure will rise up, and the liquid level will lower down;
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