Vacuum Line sizing

Values listed are guides, and final line sizes and flow velocities must be determined by appropriate calculations to suit circumstances. Vacuum lines are not included in the table, but usually tolerate higher velocities. High vacuum conditions require careful pressure drop evaluation. 

Determine the proper line size for a 350 equivalent feet vacuum jet suction line drawing air at 350°F, at a rate of 255 Ibs/hr with an initial pressure at the source of 0.6 in. Hg. Abs. Assume 10-in. pipe reading Figure 2-43. Note watch scales carefully. 

The choice of vacuum pumps for the sample preparation line will depend on the size of its volume and the budget. In general it is advantageous to have somewhat higher pumping speeds available for the vacuum line, but this can well be provided by a conventional oil diffusion pump, which is less expensive than a turbomolecular device, backed again by a rotary pump. 

A typical arrangement of components in a tensimetric titration is presented in Fig. 9.5, which shows the previously discussed tensimeter and a calibrated bulb attached to a vacuum line.2 The sample container on the tensimeter is fitted with a small reciprocating stirrer which consists of a thin glass rod connected to a glass-encased headless nail or glass-encased bundle of soft iron wire. This stirrer is driven by an external solenoid, the field of which is switched on and off by a current-interrupting device, the details of which are laid out in Fig 9.6. The size of the calibrated bulb is chosen so that it will contain the desired amount of gas for each addition at a pressure which is convenient and accurately measured (e.g., 100-500 torr). The calibration procedure and steps used dispensing gas from such a bulb are described in Section 5.3.G. 

Safety pipetting aids Mouth pipeting is prohibited it is a potential source of infection either by ingestion or by inhalation. All safety pipetting aids control contamination of the suction end of the pipet and leakage from the pipet tips. Vacuum lines used to aspirate liquids are protected with liquid disinfectant traps and cartridge-type filters (0.45 pm pore size). 

Maintain the vacuum constant over the suction time (5 to 45 min, depending on the particle size and the adsorbent quality). Immediately after the top of the column bed falls to dryness disconnect the vacuum line. 

Into a dry tube fitted with a Youngs tap and a Quickfit joint (ofthe type used to polymerize butyl acrylate in Protocol 1) is placed a small piece of sodium (about the size of a match-head). The tube is connected to the manifold or a vacuum line, evacuated and a sodium mirror formed (as for potassium above.) The tube is then cooled ( 78°C, dry ice/acetone) and ethylene oxide (ca. 8 mL) is added from the cylinder. The tube is then held at -10°C for 24 h. After this time the liquid is once again connected to the gas-line, frozen (liquid nitrogen), and the tube evacuated. An identical tube containing a sodium mirror is also prepared on the same line and cooled to 78°C. The first tube is allowed to return to room temperature and ethylene oxide is then transferred by virtue of its low vapour pressure. The second tube is then isolated from the system and once again allowed to stand under vacuum for 24 h. 

Dry vacuum pump size for usual discharge pressure 20-35 kPa gauge to allow for downstream discharge. Vacuum pumps run hot 50-70 °C. Allow 30 min warmup period before putting on-line. Allow 60 min purge before shutdown. Try not to have the pump discharge into a common header. Multistage pumps... 

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