Pump and purge

Pump and Purge. A key objective of cannula techniques is to achieve very low partial pressures of oxygen without the use of time consuming high vacuum techniques, and this is achieved by repeated pump and purge cycles. Even a heavily used rotary pump will give an ultimate vacuum of 1 x 10 2 mm Hg, and will rapidly reduce the pressure in a small reaction vessel to 1 m Hg. In a typical example a 224 mL reaction vessel contains approximately 2 mmol of O2, and evacuation to 1 mm Hg reduces the quantity of 02 to 2 x 10 3 mmol. If the vessel is refilled and the cycle repeated the quantity of O2 reduces to 2 x 10 mmol, and it is clear that relatively poor vacuums are sufficient to provide very low effective partial pressures of O2 after 2 or 3 pump/purge cycles. 

The vacuum plate drwer is provided as pari of a closed system. The vacuum dryer has a cylindrical housing and is rated for fiill-vacuum operation (typical pressure range 3-27 kPa absolute). The exhaust vapor is evacuated try a vacuum pump and is passed through a condenser for solvent recovery. There is no purge-gas system required for operation under vacuum. Of special note in the vacuum-drying system... 

MISCELLANEOUS TECHNIQUES Freeze-pump-thaw and purging... 

A typical lubrication oil system is shown in Figure 15-1. Oil is stored in a reservoir to feed the pumps and is then cooled, filtered, distributed to the end users, and returned to the reservoir. The reservoir can be heated for startup purposes and is provided with local temperature indication, a high-tempera-ture alarm and high/low level alarm in the control room, a sight glass, and a controlled dry nitrogen purge blanket to minimize moisture intake. 

Program the pump to purge out the column and shut down the pump automatically after the sample sequence. 

The vendor claims that Quick-Purge costs up to 50% less than traditional remediation methods such as pump-and-treat or soil vacuum extraction (D14386M). 

The solvent chamber should have a capacity of at least 500 mL for analytical applications, but larger reservoirs are required for preparative work. In order to avoid bubbles in the column and detector, the solvent must be degassed. Several methods may be used to remove unwanted gases, including refluxing, filtration through a vacuum filter, ultrasonic vibration, and purging with an inert gas. The solvent should also be filtered to remove particulate matter that would be drawn into the pump and column. 

The tube method involved insertion of precleaned acrylic tubes (5-cm diameter) into the littoral zone sediments at a lake-water depth of about 1 m (about 15 cm into sediments). Lake water within the tube was removed by using a peristaltic pump and Teflon line. Once the tube was purged of lake water, groundwater was allowed to fill it to a depth of about 25 cm. The tube was then purged three times with groundwater before obtaining the sample. 

Figure 18.1 Diagram of the glass vacuum line showing the major components mechanical pumps, diffusion pump, vacuum gauge, main vacuum manifold, and purge valve.

Fig. 1.21. Typical assemblies of Schlenk ware. Commercial apparatus is illustrated similar apparatus with O-ring joints in place of standard taper joints is preferred by the authors. (

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