Vacuum system rotary pump

A cryogenist does not usually need a general purpose mass spectrometer, but the cryogenist cannot work without an LD which is made up of a small vacuum system (rotary pump or diaphragm pump in series with a turbo pump) and a mass spectrometer for the detection of light gases (H2,3He and 4He). 

Few of the naturally occurring elements have significant amounts of radioactive isotopes, but there are many artificially produced radioactive species. Mass spectrometry can measure both radioactive and nonradioactive isotope ratios, but there are health and safety issues for the radioactive ones. However, modem isotope instmments are becoming so sensitive that only very small amounts of sample are needed. Where radioactive isotopes are a serious issue, the radioactive hazards can be minimized by using special inlet systems and ion pumps in place of rotary pumps for maintaining a vacuum. For example, mass spectrometry is now used in the analysis of Pu/ Pu ratios. 

In 1840 a hydrauHc power network, which involved large reciprocating pumps that were driven by steam engines, suppHed fluid power to London. However, concurrent technology in steam (qv) turbines and the electric generators outmoded such networks until hydrauHc systems were improved with the use of rotary pumps and oil. The rotary piston pump marked the transition from use of water to oil as the hydrauHc fluid (4). The use of vacuum-distilled, refined mineral oils were instmmental in the success of rotary axial piston pumps and motors such as the Waterbury variable speed gear... 

Two vacuum systems are used to provide both the high vacuum needed for the mass spectrometer and the differential pumping required for the interface region. Rotary pumps are used for the interface region. The high vacuum is obtained using diffusion pumps, cryogenic pumps, or turbo pumps. 

A continuous rotary filter is required for an industrial process for the filtration of a suspension to produce 0.002 m3/s of filtrate. A sample was tested on a small laboratory filter of area 0.023 m2 to which it was fed by means of a slurry pump to give filtrate at a constant rate of 12.5 cm3/s. The pressure difference across the test filter increased from 14 kN/m2 after 300 s filtration to 28 kN/m2 after 900 s, at which time the cake thickness had reached 38 mm. What are suitable dimensions and operating conditions for the rotary filter, assuming that the resistance of the cloth used is one-half that on the test filter, and that the vacuum system is capable of maintaining a constant pressure difference of 70 kN/m2 across the filter ... 

Example The vacuum system of non-benchtop mass spectrometers consists of one to three rotary vane pumps and two or three turbo pumps. Rotary vane pumps are used for the inlet system(s) and as backing pumps for the turbo pumps. One turbo pump is mounted to the ion source housing, another one or two are operated at the analyzer. Thereby, a differentially pumped system is provided where local changes in pressure, e.g., from reagent gas in Cl or collision gas in CID, do not have a noteworthy effect on the whole vacuum chamber. 

A clean and dry vacuum system (qpy = 0) with V = 2000 I (as in example 1) is to be pumped down to a pressure of Pend - 10 tAbar. Since this pressure is smaller than the ultimate pressure of the rotary piston pump (Sg max ... 

Almost all the high vacuum systems with which we will be concerned have at one end a rough pump, usually a rotary oil pump, capable of attaining ca. 10 Torr. This is followed by a high vacuum pump which can attain ca. 10 Torr, which is followed by a cold trap, the purpose of which is to condense out any volatile matter to prevent it entering, and possibly... 

A vacuum system composed of a combination of a rotary pump and an oil diffusion pump is frequently used. Although use of a rotary pump alone can reach low pressures of 1—10—2 Torr, use of both rotary and oil diffusion pumps is desirable because less gas remains in the reaction chamber. 

Two widely used vacuum pumps are the mechanical rotary oil-seeded pump and the vapor pump. The former provides a medium vacuum and works relative to the atmosphere. The vapor pump, on the other hand, provides a high or very high vacuum and operates relative to a medium vacuum provided by a rotary pump, referred to as a backing pump in this connection. Thus, the most widely used high-vacuum system able to establish an ultimate pressure of about 10-< torr or below consists of a vapor pump backed by a rotary pump. 

Other vacuum pumps include the sorption type based on the high gas take-up of charcoal or moleculai sieve material at liquid nitrogen temperatures. Sorption pumps may be used in place of rotary pumps, with a desirable freedom from rotary pump oil vapor, especially in systems where the amount of gas to be handled is limited. 

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. 

The tubing between the vacuum system and diffusion pump must have as few restrictions (in size and shape) as possible. Glass or rotary stopcocks with bores from 12 to 15 mm minimum (on the system side of the diffusion pump) will help to ensure minimum hold-up. In addition, tubing in these areas should be as straight (unkinked, with few bends) as possible. 

Vacuum systems (Fig. 21-12 ) are characterized by material moving in an air stream of pressure less than ambient. The advantages of this type are that all the pumping energy is used to move the product and that material can be sucked into the conveyor line without the need of a rotary feeder or similar seal between the storage vessel and the conveyor. Material remains suspended in the air stream until it reaches a receiver. Here, a cyclone separator or filter (Fig. 21-12c) separates the material from the air, the air passing through the separator and into the suction side of the positive-displacement blower or some other power source. 

A modest vacuum source (about 20 - 50mmHg) should be available at each bench and is sufficient for rotary evaporation of most solvents, filtering under vacuum, distillation of relatively volatile oils, and similar tasks. This level of vacuum is sometimes provided by a house vacuum system. Alternatively, a water aspirator or small diaphragm pump can be used. 

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