overview of vacuum systems
DESCRIPTION
Overview of Vacuum Systems. Tejas Deshpande 24 July, 2014. Outline. Introduction Pumps Positive displacement pumps Momentum transfer pumps Entrapment pumps Pressure gauges Vacuum seals Manipulation and motion under vacuum. Introduction. Introduction: definitions. - PowerPoint PPT PresentationTRANSCRIPT
Overview of Vacuum SystemsTejas Deshpande24 July, 2014
• Introduction
• Pumps
• Positive displacement pumps
• Momentum transfer pumps
• Entrapment pumps
• Pressure gauges
• Vacuum seals
• Manipulation and motion under vacuum
Outline
Introduction
Introduction: definitionsKinetic Theory of Gases
• Ideal gas equation
• Velocity of molecules hitting chamber walls
Pumping
• Rate of mass flow
• Mass “conductance”
Introduction: definitions
http://fisica.ufpr.br/sharipov/tubefm.html
Pumping
• Pump capacity & effective pumping speed
Introduction: definitions
• Rate of evacuation
• Example: Pfeiffer Hena-25 pump + cylindrical chamber
• Finite C with a hose
Pumping
• Conductance of KF 40 hose (L = 10", D = 2.165")
Introduction: definitions
[1] http://www.vacuumlab.com/Articles/Knowing%20Eff%20Pump%20Speed.pdf
[1]
Rotary vane pumps
• Principle of operation
Positive displacement pumps
Scroll pumps
• Principle of operation
Positive displacement pumps
Diaphragm pumps
Positive displacement pumps
• Principle of operation
Roots “blower”
Positive displacement pumps
• Principle of operation
Diffusion pumps
• Air diffuses to vapor stream
• Baffles condense vapor
• Oil backstreaming problem
Momentum transfer pumps
Turbomolecular pumps
• Principle of a molecular “drag” pump
• Mechanically similar to rotary pump
• Good compression ratio
• Poor pumping speed
• Turbo pump
Momentum transfer pumps
Turbomolecular pumps
Momentum transfer pumps
• Principle of operation
Ion pumps
• Penning cell
• Magnetic field acts as electron trap cyclotron orbits
• Ions deposit on Cathode
Entrapment pumps
Titanium sublimation pumps
• Titanium as evaporatable “getter” material
• Chemical sorption
• 40-50 Ampere current evaporates Ti
Entrapment pumps
Liquid Manometers
• Simplest U-tube manometer
Pressure gauges
• Atmospheric pressure = 1 bar
The Diaphragm Manometer
• Capacitive sensor
• AC vs. DC
• DC capacitance bridge
• AC resonant circuit tuned to diaphragm vibration
Thermal Conductivity Gauges
• Convection of heat through the gas
Pressure gauges
• Other heat losses
• Radiation ~ T4
• Solid conduction
• Operating conditions
• Free molecular flow
• > 10-3 torr
Ion Gauge
• Measurement of ion current
Pressure gauges
• Gauge sensitivity
• Bayard-Alpert gauge
• Collector potential: -10 V• Grid potential: 180 V• Cathode filament: 30 V• Screen: 0 (ground)
O-ring seal
• Elastomers, Viton-A, Polyimide
• Quick and reusable
• Limited baking range (< 250 °C)
Vacuum Seals
ConFlat flange seal
• “Leak-tight” (< 10-12 Pa m3s-1)
• Metal gaskets (typically copper)
• Bakable to 450 °C
• Not reusable
Metal bellows
• Mechanical feedthroughs
• Bakable to 450 °C
• Limited linear/angular stroke
Manipulation and motion under vacuum
Continuous rotation
• Speeds up to 2000 RPM
• High torque bellows
• Low torque magnets
Gate Valve
Manipulation and motion under vacuum
Right-angled valve
• Large bore
• Sample transfer
• Small bore
• Air evacuation
Transfer arm
Manipulation and motion under vacuum
• Significantly greater stroke than bellow-sealed manipulator
• Magnetic power transmission
• Introduction
• Pumps
• Positive displacement pumps
• Momentum transfer pumps
• Entrapment pumps
• Pressure gauges
• Vacuum seals
• Manipulation and motion under vacuum
Summary