DIFFUSION PUMPS (Fig. 7) Oil diffusion pumps are most commonly used for industrial processing in the10 to Pascal range. This type of pumping system is the lowest first cost for its pressure range, but cryogenic cold trapping must be used for processes sensitive to backstreamed oil. Diffusion pumps are available in a wide range of sizes. Diffusion Pumps • Si oil is boiled and vaporized in a multistage jet assembly. • Oil vapors emerging from the nozzles impart momentum on the residual gas molecules and drive them towards the bottom of the pump. • The molecules are compressed and exhausted. • No vibrations. Figure 11.2 Cutaway drawing of a cryo-sorption vacuum pump. TC 1 vacuum vessel Figure 11.3 Schematic of a vacuum vessel rough pumped by a bank of three cryo-sorption pumps. Several cryo-sorption pumps may be arranged in a bank as shown in figure 11.3. This configuration has several advantages over the use of a single cry-sorption pump. A the mechanical and diffusion pumps. 5. Roughing Line and Valve Exposure to atmosphere when at operating temperature will result in decomposition of diffusion pump oil. It is therefore necessary to employ a bypass line around a heated diffusion pump when evacuating a chamber from atmospheric pressure to a "rough" vacuum prior to connecting the The oil diffusion pump is operated with an oil of low vapor pressure. The high speed jet is generated by boiling the fluid and directing the vapor through a jet assembly. Note that the oil is gaseous when entering the nozzles. Within the nozzles, the flow changes from laminar to supersonic and molecular. Pump body Stainless steel Nozzle Aluminum Cooling method Water cooling pipe Oil level gauge None None Optional Attached Weight kg 7.5 13.5 47 56 Shipping measurement (Height x Width x Length) 550 x 330 x 400 580 x 420 x 580 730 x 550 x 700 750 x 550 x 700 Shipping weight kg 10.5 17.5 54 64 Dimensions Inlet diameter Outside diameter Materials A review of major advances in diffusion pump technology in the sixties is presented. The discussion is limited to oil diffusion pumps, their optimum design parameters, performance evaluation, and application experience. Significant improvements have been achieved since the beginning of space-related applications (1957). Vacuum Pumps Mechanism Gas transfer Gas capture Function Roughing (backing, mechanical pumps) Rotary vane Sorption Rotary lobe Scroll ScrewSorption, Rotary lobe, Scroll, Screw High vacuum Oil diffusion, Turbomolecular, Cryo, Ion Auxiliary Titanium Sublimation, LN 2 16Liu, UCD Phy250-1, 2011, NanoFab Oil diffusion pumps attain high vacuum, and are used as the exhaust system for a wide variety of vacuum processes such as vacuum heat treatment, vacuum evaporation, electric beam welding, and sputtering. The lineup includes pumps with an volume flow rate of 10,000L/s or higher (without baffles). This is a highly reliable high vacuum pump with Pipet the old oil from the diffusion pump and wash with hexanes. Dry the inside of the diffusion pump. The basic components of the diffusion pump, including the jet assembly, should also be cleaned and washed with hexanes. Following this, 100 cc of new 702 Dow Corning Silicone Oil should be poured into the diffusion pump. The diffusion pump was the first type of high vacuum pump operating in the regime of free molecular flow. Due to its simplicity, high performance and low initial cost, the diffusion pump remains a primary industrial high v