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Chapter 4

Summary Vacuum pumps and pumping systems

The chapter ‘Vacuum pumps and pumping systems’ extensively discusses all nowadays commercially available pump principles at the hand of important qualities, such as throughput, pumping speed, ultimate pressure, compression ratio, gas type dependency and working range. In addition, more specific characteristics of a particular type of pump are discussed in the section treating this pump. Since the 1980’s the pump palette has made a clear shift from wet to dry pumps. With ‘wet’ we mean pumps which need a liquid for their pumping action. Liquids in pumps because of several reasons (unsurmountable contamination problems, increasing costs of maintenance and ever higher environmental costs because of stricter regulations) became impermissible in various applications of vacuum in research and industry and gave a great impetus to the development of dry pumps. Transition from wet to dry pumps nowadays is considered as an economically attractive alternative. With respect to the Dutch version of this book from 2000, the chapter contains several major changes and significant innovations. In summary, the chapter is extended with attention to the multi-stage Roots pump, which in the past decade has rapidly developed into a valuable alternative to the claw pump and is able to discharge to atmospheric pressure. As for the claw pump, new insights are incorporated about the use of an integrated combination of Roots and claw stages. Concerning the screw pump, attention is paid to the tapered pitch as a solution to reduce the heat generated by isochoric compression. The section ‘Molecular pumps’ is extended with a paragraph on the molecular drag pump (MDP)/side channel pump combination, consisting of a Holweck type molecular drag pump and multiple stage miniature type of side channel blower. This pump combination also appears to be able to discharge against atmospheric pressure. The required knowledge regarding the side channel blower is added to the section ‘Dry rotary pumps’. Finally, the section ‘Sputter-ion pumps’ is supplemented with information on the so-called ‘Galaxy’ and ‘StarCell’ cathode structures to increase the pumping speed for noble gases.

Some figures in Vacuum pumps and pumping systems

Vacuum pumps and pumping systems - Cross section of a liquid ring pump — Cross section of a single-stage liquid ring pump. 1 – pump intake, 2 – pump exhaust, 3 – liquid ring, 4 – impeller, 5 – suction port, 6 – discharge port

Vacuum pumps and pumping systems - Liquid ring pumps — (a) and (b) – external view of respectively a single-stage and a two-stage liquid ring pump, (c) – disassembled single-stage pump

Vacuum pumps and pumping systems - Cross section of a water-cooled two-stage oil-sealed multivane pump — Cross section of a water-cooled two-stage multivane pump without a non-return valve in the exhaust. 1 – intake, 2 – pressure relief valve, 3 – oil reservoir for the first (low pressure) stage, 4 – oil reservoir for the second (high pressure) stage, 5 – exhaust filter, 6 – filter cartridge, 7 – exhaust, 8 – water cooling

Vacuum pumps and pumping systems - Modern oil diffusion pump in cross section — Example of a modern oil diffusion pump. 1 – boiler with pumping fluid, 2 – large top reverse cap underneath a water-cooled hat, 3 – side ejector jet, 4 – local widening of the pump body to increase the pumping speed, 5 – water cooling, 6 – high vacuum inlet flange, 7 – condenser with backing-line connection.

Vacuum pumps and pumping systems - Diaphragm pump in cross section — Schematic cross section of a diaphragm pump. I – inlet valve, O – exhaust valve, D – diaphragm, E – rotating excenter.

Vacuum pumps and pumping systems - Cutaway view of a single-stage side channel blower — Cutaway view of a single-stage side channel blower. 1 – inlet, 2 – side channel, 3 – rotor vanes, 4 – exhaust, 5 – local constriction of the side channel, 6 – motor, 7 – swirling spiral movement of gas in the side channel (source: Elmo Rietschle)

Vacuum pumps and pumping systems - Dry multivane pump in cross section — Schematic cross section of a dry multivane pump (single-stage). 1 – intake, 2 – pump volume in between the rotor vanes, 3 – exhaust

Vacuum pumps and pumping systems - Cutaway view of a Roots pump — Cutaway model of a Roots pump. 1 – gear wheels, 3 – pump body and gearbox, 4 – figure-of-eight shaped rotors, 7 – oil supply pot to provide the interspace between the oil seals 8 with lubricant, 8 – lip seals, 9 – motor, 11 and 13 – shaft bearings (source: Pfeiffer Vacuum)

Vacuum pumps and pumping systems - Cross section of a Roots pump with bypass line — Roots pump with bypass line. 1 – inlet, 2 – rotors, 3 – exhaust, 4 – pump body, 5 – gravity-operated pressure relief valve (source: Alcatel Vacuum Technology)

Vacuum pumps and pumping systems - Rotor set of a modern screw pump with varying pitch — Photograph of the rotor set of a modern screw pump with a varying pitch. At the inlet side (left-hand side in the photo) the pitch is large and reduces towards the exhaust side at the right-hand side in the photo (source: Pfeiffer Vacuum)

Vacuum pumps and pumping systems - Molecular drag pump (MDP) in cross section — Cross-sectional view of a molecular drag pump (MDP) with two Holweck stages (source: Alcatel Vacuum Technology)

Vacuum pumps and pumping systems - Cutaway view of an MDP/side channel pump with side channel blower in a radial arrangement — Cutaway view of an MDP/side channel pump with side channel blower in a radial arrangement. 1 – inlet port with splinter guard, 2 – rotor first Holweck stage, 3 – rotor second and third Holweck stage, 4 – rotor fourth and fifth Holweck stage, 5 – rotor shaft, 6 – impeller rings of side channel blower, 7 – exhaust, 8 – cooling water connections, 9 – side channels (6 stages), 10 – stator fifth Holweck stage, 11 – stator third and fourth Holweck stage, 12 – stator first and second Holweck stage. (source: Edwards Vacuum)

Vacuum pumps and pumping systems - Hybrid molecular pump (HMP) in cross section — Cross section of a hybrid molecular pump with drum-MDP and hybrid bearing. 1 – high vacuum connection flange, 2 – rotor of the TMP section, 3 – stator of the TMP section, 4 – vent valve, 5 – stationary cylinders of the drum-MDP with helical pump channels, 6 – concentric drums of the MDP, 7 – purge gas connection, 8 – cooling water connection (only during bakeout), 9 – ceramic bearing with oil lubrication, 10 – oil reservoir, 11 – mains socket, 12 – motor, 13 – backing vacuum connection, 14 – permanent magnet bearing, 15 – dry running limiter bearing (source: Pfeiffer Vacuum)

Vacuum pumps and pumping systems - Hybrid molecular pump provided with Gaede type MDP — Cutaway view of a hybrid molecular pump (HMP) provided with a Gaede disc-MDP (source: Edwards Vacuum)

Vacuum pumps and pumping systems - Schematic of a classic diode sputter-ion pump element — Sketch of the pump element of a classic diode sputter-ion pump and schematic overview of pump mechanisms. A – anode cylinders, B – magnetic field, C – titanium cathodes.

Vacuum pumps and pumping systems - Galaxy diode pump element — Pump element of a Galaxy diode pump. The spiral-shaped slots in the cathodes are axially centered relative to the anode cylinders (source: Duniway Stockroom Corporation)

Contents Vacuum pumps and pumping systems

4.1     Introduction 160
4.2     Definitions 163
4.3      Compression processes in transfer pumps 166
4.4      Liquid-sealed rotary pumps 168
4.4.1   Liquid ring pump 168
4.4.2   Rotary vane pump 175
4.4.3   Gas ballast 181
4.4.4   Oil-sealed multivane pump 189
4.4.5   Rotary-piston pump 190
4.4.6 Oil-sealed rotary pumps in practice; pump accessories 193
4.5      Liquid jet pump 198
4.6      Vapour-stream pumps 199
4.6.1   Steam jet pump 208
4.6.2   Diffusion pump 211
4.6.3   Pump fluids 223
4.6.4   Diffusion pump system operation 225
4.6.5   Hints and safety measures for diffusion pump systems 228
4.6.6 Vapour booster pump 229
4.7      Oscillation pumps 230
4.7.1   Piston pump 231
4.7.2   Diaphragm pump 233
4.8      Dry rotary pumps 235
4.8.1   Side channel blower 235
4.8.2   Oil-free multivane pump 239
4.8.3   Scroll pump 240
4.8.4   Roots pump 243
4.8.5   Claw pump 260
4.8.6   Screw pump 268
4.9      Molecular pumps 270
4.9.1   Molecular drag pump (MDP) 272
4.9.2   MDP/side channel pump 280
4.9.3   Turbo molecular pump (TMP) 285
4.9.4   Design and engineering aspects of turbo molecular pumps 293
4.9.5   Turbo molecular pump system operation 301
4.9.6   Hybrid molecular pump (HMP) 303
4:10     Capture pumps 307
4.10.1  Sorption pump 308
4.10.2 Getter pump 318
4.10.3 Sputter-ion pump 325
4.10.4 Cryopump 335
4.10.5 Cryopump system operation 348
4:11      Pump selection 351
4.11.1 Quantity of gas (throughput) Q to be pumped 351
4.11.2 Desired operating pressure p 352
4.11.3 Required pumping speed S 353
4.11.4 Economic aspects 353
4.11.5 Pumping aggressive, toxic or explosive gases and vapours 354
4.11.6 Pumping large amounts of gas 356
4.11.7 Obtaining ultra-high vacuum 358
exercises

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