Turbo pumps

Because of the low viscosities of cryogenic Hquids, rolling element bearings seem better suited than hydrodynamic bearings for turbo pumps. AISI 440C stainless balls and rings generally are preferred for their corrosion resistance over the more commonly used AISI 52100 steel. 

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. 

QMS) and an ellipsometer complete the setup. The typical pressure is in the range of 0.15-0.5 mbar. The deposition chamber has a volume of 180 1. During processing it is pumped by a stack of two Roots blowers and one forepump (total pumping capacity is about 1500 m /h) otherwise it is pumped by a turbo pump (4501/s), with which a base pressure of 10 mbar is reached. 

Fig. 1.1. Experimental setup for electrochemical on-line mass spectroscopic measurements with automatic data acquisition. TP = Turbo pump, IC = inlet chamber, A = analysis chamber, S = Screw mechanisms to control aperture between both chambers.

Fig. 1.3. Experimental setup for electrochemical thermal desorption mass spectroscopy (ECTDMS). C = electrochemical cell, W = working electrode, El = electrolyte inlet, EO = electrolyte outlet, EH = electrode holder, V = valve, TP = turbo pump, VC = vacuum chamber, L = light source, W = window, P = protective jacket, A = aperture to analysis chamber, GI = grid ion source, S = SEM detector.

Turbomolecular (turbo) pumps are very clean (especially magnetically levitated version) mechanical pumps, with pumping speed up to more than 70001/s. 

With metal gaskets and moderate bakeout, turbo pumps can reach pressure below 10-9 torr without traps. They can be started at a pressure up to 1 torr. The time required to reach full pumping speed ( lmin) is much shorter than for diffusion pumps. Also these pumps must be backed by a primary pump. 

The turbo pumps are made up of lCMO rotating (rotor) and fixed (stator) disks (see Fig. 1.16 and Fig. 1.17) alternatively arranged. Each disk has 20-60 blades with proper tilt. 

The motor (usually working in vacuum) is moved by a special current power supply. The rotor turns at 104-105rpm, usually a multiple of the line frequency. The pumping speed of a turbo pump unit depends on its rotational speed. High-speed turbo pumps need more frequent maintenance interventions. In some turbo pumps, a low-speed mode allows operation up to 10 1 torr. However, full rotational speed is achieved at pressures... 

Fig. 1.18. Typical pumping speed of a turbo pump for nitrogen, helium and hydrogen.

Light gases with higher thermal velocity are pumped less than heavier ones. This is why turbo pumps produce an (almost) oil-free vacuum. The lubrication of turbo pumps is made with a special vacuum grease. Pumps with magnetically levitated rotor are available, but they are more expensive. 

Molecular drag pumps vary from turbo pumps in that the momentum is transferred to the gas molecules not by blades but by a rapidly rotating solid surface. The stator is, in this case, a fixed surface very close to the rotor (see Fig. 1.19). 

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). 

Four Varian 550 turbo pumps are used in parallel. They are backed up by an Edwards mechanical booster (2500 m3/h) and a Pfeiffer uni-dry (60m3/h). A maximum circulation rate could be achieved at about 7 mmole/s. The 3Fie pumping tube is inserted from the top of the cryostat. 

The use of an Aldrich Kugelrohr oven allowed for distillation in a large flask. This is advantageous, since decomposition may ensue above 100°C.2 For this reason distillation has to be carried out at as low a pressure as possible. In most cases the submitters used a turbo pump, but application of a normal high vacuum pump with a distillation temperature of 90°C at 0.04 mm is also possible. 

The schematic diagram of the system is shown in Fig. 3—4. An electrochemical cell is connected to the recipient chamber, whose vacuum is controlled independently using a turbo pump located just below it. A small... 

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. 

Cryopumps adsorb (freeze) residual gas to a surface cooled to the temperature of liquid nitrogen. They are highly efficient and silent and provide clean vacuum, but cannot be operated without interruptions to recover the adsorber. Cryopumps are typically operated in combination with turbo pumps because they are only started after high vacuum conditions are reached. Otherwise, the adsorber would soon be saturated. 

When a turbo pump is used to obtain high oxidizer fuel flow, this is also operated by the fuel-rich gas generated in the primary combustor. Since the fuel-rich gas is at a higher pressure than the pressure in the secondary combustor, it is used to operate the oxidizer pump and is then used as a fuel component in the secondary... 

Fig. 14.24 Two types of gas-hybrid rocket gas-pressurized system and turbo pump operation system.

Space technology Turbo pump of the space shuttle radar windows for rockets... 

Presently a commercially available two stage vacuum system comprising a membrane (Pfeiffer MVP 006-4) and a turbo pump (Pfeiffer HiPace 10) in combination with a pressure sensor (Leybold Vacuum Ionivac ITR 90) establish a pressure of about 0.1 Pa in the system. Three electric valves are used to control the gas flow into the capillary system and for the bypasses. The use of macro devices simplifies the handling of the experimental setup and also the electronic control. Pressure drops for plasma and sample gases are accomplished by an appropriate combination of capillaries with different diameters and lengths as described in Sect. 4. 

Presently the electronics controlling the pumps and valves predominantly protect the turbo pump and the PIMMS from damage. Since the high voltages driving the system could initiate detrimental arc discharges between electrodes and metal structures, they are only to be applied at low pressure. Therefore, this control of high priority is supplied by an independent unit. 

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