E liquid level will rise up; the pressure difference between D and E liquid levels is balanced with the pressure of the right side water vapors. The more the water vapors, the higher such pressure becomes; while the liquid level will rise up or lowers down more considerably. When the moisture content amounts to a certain value, and the water vapor pressure amounts to the critical point of saturated vapors, some of the water vapors recondenses into water (in forms of fog or beads), and the pressure will not rise up any more. The moisture content corresponding to such critical point of saturated vapors is just the highest water content detected by this device.

Moisture determination by the pressure difference method uses a pairing method. Various known moisture contents are respectively used to examine and determine the different D, E liquid level rises or falls correspondent to different moisture contents. Therefore, when substances with unknown moisture contents are examined, their moisture contents may be determined according to the different D, E liquid level rises or falls.

Domestic manufacturers frequently apply this method to determine water contents of dried polyester slices and nylons, under a general examination temperature at:
Polyester chip                                 220±5˚C
Polyamide 6, 66, 69, 610, 612         195±5˚C
Polyamide 11, 12                            170±5˚C

The moisture determination device by pressure difference method is mainly composed of the following measuring part, and vacuum pump, heating part and temperature control part:

• Measuring part
Measurement part is shown in figure 1; it is composed of a set of glass structure, a vacuum pump, and a vacuum gauge; and a very good air tightness of the entire structure is required. The vacuum pump enables measurement part reach a high degree of vacuum prior to testing.

• Heating part
It is composed of a heater, a hearth and a lift platform with a cuvette suspension centering device. When the lift platform is raised up and a