Low Pressure System Components
Item # | Component | Description |
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1 | Servo isolation valve | Ensures no leaking occurs through the servo. It is open when the servo is in use and closed when the servo is off. |
2 | Fast evacuation valve | Used at the end of the evacuation routine to achieve the best vacuum. When this valve is open, the sample stations are directly connected to the vacuum system. |
3 | Vacuum valve |
The vacuum valve is opened to evacuate the back of the servo valve during the ramping part of the evacuation sequence. This allows the servo valve to control the evacuation rate. When the pressure is low enough, the evacuation through the reservoir proceeds. This is accomplished by alternately opening Valve 8 (to allow gas from the sample to move to the reservoir) and Valve 3 (to evacuate the reservoir for the next step). |
4 | Gas inlet valve | Allows pressurization at the back of the servo valve. The servo can then be used to dose pressures from 0.2 psia to 50 psia onto the low pressure stations. Dry nitrogen or argon is the preferred gas. Do not use air unless it is dried to remove water vapor. |
5 | Mercury fill valve | Mercury flows into the degasser then into the low pressure stations and is controlled by the fill valve. The drain valve allows mercury to flow back into the reservoir. |
6 | Drain valves | See Mercury fill valve [5]. |
7 | Mercury reservoir evacuation valve | Connects the vacuum line to the mercury reservoir. |
8 | Evacuation Reservoir valve | See Vacuum valve [3]. |
Low pressure ports |
A sample encased in a penetrometer is first evacuated, filled with mercury, then pressurized to between 15 and 50 psia.
Penetrometer stems inserted into a station are sealed for vacuum and against mercury leakage by compression of a soft, gum rubber cylinder near the tip. The rubber is compressed by turning the large knob or pressure collar that protrudes from the front. The inner rim of this knob serves also as the mounting mechanism for a capacitance transducer after the knob has been tightened. |
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Mercury storage reservoir | Holds 7 to 10 pounds of mercury and is located behind the front panel. The level of mercury is visible through a small window in the front panel. Before beginning a low pressure analysis, the application verifies that the level of mercury in the reservoir is adequate. | |
Mercury degasser |
Removes trapped gases as mercury passes to low pressure stations then into the penetrometer. HG Up indicator. Illuminates when mercury level fills the penetrometers. The sensor completes an electric circuit and flow is stopped by closure of the mercury fill solenoid valve. Drained indicator. Illuminates when the mercury drain valve is closed and the level of mercury in the degasser is below the level in the low pressure stations. Alarm buzzer. If the level of mercury rises above the normal filling level, the sensor causes both the mercury fill valve and the mercury drain valve to close and a buzzer alarm sounds. See Handling Mercury Overfill. |
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Mercury trap | Serves as a large volume reservoir for mercury in the event that operator error or a malfunction allows mercury to travel toward the vacuum system. If not stopped, mercury can severely damage the analyzer. Should this occur, a high-pitched, continuous alarm sounds if more than 6 mm (0.25 in.) of mercury accumulates in the trap. The fault must be corrected and the mercury removed before proceeding. |
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