Pumping systems Common problems

The method just outlined and illustrated is route specific. It is very flexible and simple to use. It can also be easily computerized if the GP data can be fed in as numerical values. Here we have illustrated its use in the context of a cross-country pipeline, such as a crude oil, products, or perhaps slurry pipeline, which might be commonly encountered by chemical engineers. The method is completely adaptable to any hydraulic flow problem and could be used equally well for a short in-plant pumping system analysis. It can help the designer of flow systems to avoid sometimes subtle traps for slack flow and siphons that might not be immediately obvious if the mechanical energy equation is applied only once between the initial and final points of the flow system. 

The most common problem with hydrocarbon diffusion pump oil is its fractionation into multivapor pressure components. As pump oil breaks down, it develops both lower and higher vapor-pressure characteristics. Oils with high vapor pressures can potentially drift into the system, although they are more likely to be effectively removed from the system by being trapped in the alembics of the central vertical tube, in the cold trap between the system and the diffusion pump, or in the cold trap between the diffusion pump and the mechanical pump. If not trapped, they are free to travel into the vacuum line itself or into the mechanical pump. Diffusion pump oils that collect in a mechanical pump are not likely to have any significant performance effects (as opposed to the degrading effects of mechanical pump oil collected in diffusion pumps). 

Under normal circumstances, there is no need for the operator to be concerned about routine maintenance of the mass analyzer. With modem turbomolecular pumping systems, it is highly unlikely there will be any pump- or sample-related contamination problems associated with the quadrupole, magnetic sector, or TOP mass analyzer. This certainly was not the case with some of the early instruments that used oil-based diffusion pumps, because many researchers found that the quadrupole and prefllters were contaminated by oil vapors from the pumps. Today, it is fairly common for turbomolecular-based mass analyzers to require no maintenance of the quadrupole rods over the lifetime of the instrument, other than an inspection carried out by a service engineer on an annual basis. However, in extreme cases, particularly with older instruments, removal and cleaning of the quadrupole assembly might be required to get acceptable peak resolution and abundance sensitivity performance. 

At a site in Ilhnois, TreeMediation was coupled with a pump-and-treat system to mitigate an immediate at-risk situation of off-site movement of a contaminated plume containing nitrogen and pesticides. This problem provided an opportunity to compare the costs of the two systems. Costs are estimated in round numbers for a 1-acre site with an aquifer 20 ft deep. Costs common to both approaches, such as meetings with regulators and laboratory analyses, were not included. Results are given in Table 1 (D12674I, p. 350). 

There are many mechanical pump designs, the most common of which is the rotary pump. It is named for its use of rotating internal parts that collect, compress, and expel gas from a system. Despite the simplicity in concept, there are very interesting mechanisms that pump manufacturers have developed to overcome the problem of mechanical pumps, namely, that they are inherently a slow pump. It is their simplicity, however, that has made them the general workhorse for creating a vacuum all over the world. 

---