Dry pumps

To maintain 10 1 mbar, Smin for the backing pump should be 76.1 Ls-1 (-275 m3h-1). This is achievable with, say, a Roots + two-stage oil-sealed rotary pump combination e.g. SRoots = 500 m3 h 1, SIotaiy = 60 m3 h 1. 

Because of the problems that can potentially arise with oil-sealed pumps, there is an increasing trend to use dry pumps in many applications. Various types are available including Roots pumps backed with suitable pumps (see Section 3.2.3), multi-stage Roots pumps, screw-, hook-and-claw- and scroll pumps. Dry piston pumps and diaphragm pumps are also available but their pumping speed range is restricted. The 

Parameter Claw Screw Scroll Piston Diaphragm 

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Obviously, in practical situations one can hardly imagine a vacuum pump installed onboard of a fuel cell-powered vehicle. Even if so, the membrane of a Proton Exchange Membrane Fuel Cell (PEMFC) will be soon contaminated by the oil vapors released from the pump (dry pumps are possible but this would enormously complicate the entire design). 

Dry pumps operating under harsh condictions in the semiconductor industry J. c. Sci. Technol. A7 (3), 1989,2381-2386... 

Evaluation of dry pumps vs rotary vane pumps in aluminium etching N cuum 41,1990,1825-1827... 

For high-performance lAC, the preferred solid support is a glass bead solid support coated wilh either protein-A or protein-A covalently linked with the antibody through a carbodiimide bond (165, 166). In either case, protein-A binds to the Fc portion of the antibody so that the combining sites are oriented to the mobile phase. Once the protein is attached, the lAC matrix is packed into the column either as a slurry or dry. Pump-slurry techniques use buffers with a low salt content, such as Tris or 0.01 M phosphate buffer to minimize friction and denaturation of the immobilized antibody (16). If the solid support consists of glass beads, the packing can be freeze-dried after antibody attachment and packed dry. 

New pumps are generally shipped with isopropanol or a similar solvent in the pump head, and this will need to be washed out. Always try and determine the history of a pump before starting it up. Systems that have not been run for a while may have dried out. If buffer was left in the pump, it may have dried and crystallized. In any event, running a dry pump can damage seals, plungers, and check-valves. 

Rotary vane/rotary piston pumps 1 -stage, p -10" mbar 2-stage, />ult - 10"3 mbar Dry pumps... 

This pumping speed is achievable using a two-stage oil-sealed rotary pump. If a dry pump, such as a hook-and-claw pump is required, then a Roots + dry pump combination would have to be used because of the limited pult of the dry pump (see Figure 3.3). 

A Roots vacuum pump with a theoretical pumping speed (Slh) of 500 m3 h l is backed by a dry pump designed for the chemical industry. Under working conditions, the dry pump has a speed of 50m3h 1. 

The maintenance of baffles and traps can be expensive both in materials and time. There are several dry pumps (see page 347) that have no grease or liquids in the pumping region. 

T-l Less 1. Tank runs dry Pump cavitates Damage to pump LIA-1, Can reagent react/... 

The most commonly used vacuum pumps are steam-jet ejectors and several positive-displacement pumps, which are shown in Figures 5.1 and 5.2. Some of the characteristics of vacuum pumps are given in Table 5.1. A prime consideration when selecting a vacuum pump is the compatihility of a gas with a seal fluid. To avoid these problems, there is a trend toward using dry pumps where a seal fluid or lubricant is not used [60]. 

The vaeuum pump sets are usually vane pumps in eombination with blowers or dry pumps. The vaeuum control is achieved through a needle valve, and the pressure (vaeuum) profile is the seeond of the indirect, product-related, most important parameters for cycle validation. 

A liquid ring vacuum pump or a mechanical dry pump is used. Operating pressures are in the range of 1 to several hundred Torr over the time inten/al of one cycle. Operating pressures and temperatures are just below the saturation temperature for the operating fluid. 

Q. There are other types of vacuum pumps, seldom found in cleaning machines. A fifth type of pump is a dry pump, which can be a screw, scroll (high speed), or claw design. Booster pumps are also dry and a generally rotary lobe type. 

Dry pumps can produce very high levels of vacuum in a booster role. Some screw pumps can reach less than 0.1 Torr absolute. 

However, one has to consider the limited lifetime and chemical compatibility of gaskets and diaphragms of the dry pumps before they are used in specific processes. 

Oil-free (relatively) or dry pumps have been developed to meet the needs of processes that generate particulates or reactive species that degrade the pump oils. In addition, they are relatively oil-free, thus avoiding the potential of oil contamination in the deposition system. Dry pumps are more tolerant of particulates than are oil-sealed mechanical vane pumps. 

The former can have gas injection ports to allow purge gases to be introduced to aid in sweeping particulates through the pump. Generally, dry pumps are noisy and bulky. 

Dry pump (vacuum technology) A vacuum pump that uses no (or little) oil, which can become a source of contamination. See also Vacuum pump. 

Dry pumping (contamination control) Vacuum pumping using one or more dry pumps to avoid the possibility of oil contamination. Example A turbopump with a molecular drag stage backed by a diaphragm pump. 

Oil-free vacuum pump (vacuum technology) See Dry pump. 

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