This educational seminar discusses creating, measuring, and troubleshooting Rough Vacuum.

Specifically, today’s talk will cover:• Brief review of Vacuum Fundamentals• Applications Using Rough Vacuum• Rough Vacuum Pumps• Rough Vacuum Gauges• Troubleshooting Rough Vacuum Applications• Summary and Preview of High Vacuum Webinar

Previous Webinar (Vacuum Fundamentals) is available for download at:http://www.agilent.com/en-us/training-events/eseminars/vacuum

Vacuum History Review

• Credited with first Vacuum Pump• Magdeburg Experiment (1657)

Von Guericke(1602-1686)

Varian Brothers (1898-1961)

• Vacuum Tubes for Radio & Radar applications (Klystron linear vacuum-tube amp)

• Invented ‘sputter-ion’ pump to improve tube life (1956)• Inventors of Nuclear Magnetic Resonance (NMR)

2010

Pressure: Molecular Collisions

Momentum transfer from a particle hitting a fixed surface creates a Force on the wall.

P = F/A

P1F1

F1 F2

PT

MOLECULAR FLOW VISCOUS FLOW (P < 1 mTorr) (P > 100 mTorr)

Flow Regimes: Viscous vs Molecular

Conductance in Viscous Flow (> 100 mTorr)

In Viscous Flow, the Conductance of a TUBE can be calculated using the formula:

C = 180 D4 x P/L (l/sec)D = Diameter of tube in cmL = Length in cmP = Pressure in Torr

L (cm)

D (cm)

Diameter Conductance (m3/hr)

¼” 0.151” (NW25) 37

1.5” (NW40) 1902” (NW50) 600

Snet = (C x S) (C + S)

Conductance of 1m (100 cm) tubing sizes at 500 mTorr

In Viscous Flow, the Conductance of a TUBE can be calculated using the formula:

L (cm)

D (cm)

Diameter Conductance (cfm)

¼” 0.11” (NW25) 22

1.5” (NW40) 1122” (NW50) 353

Conductance of 1m (100 cm) tubing sizes at 500 mTorr

Snet = (C x S) (C + S)

C = 180 D4 x P/L (l/sec)D = Diameter of tube in cmL = Length in cmP = Pressure in Torr

Conductance in Viscous Flow (> 100 mTorr)

Pressure Regions: Rough Vacuum UHV

Pressure (Torr)

Vacuum Pressure Regions

Rough Vacuum

UltraHigh

Vacuum

High Vacuum

Tran

sitio

n

Rough Vacuum Applications

Instrumentation & Mass Spec- ‘Backing’ High Vacuum Pumps- ‘Interface’ Pumping (Differential

Vacuum)

Vacuum Coating- Surface coatings for

decorative or structural properties

Detector

Rough Vacuum PumpEvacuates ‘Interface’ region to a few Torr AND acts as ‘Backing’ pump for the Turbo

1 x 10-3 Torr 1 x 10-5 Torr

1 – 3 Torr DUAL-INLET Turbo PumpsSingle Pump evacuates multiple vacuum regions at different pressures

Rough Vacuum Applications

Automotive- Leak Detection (AC & Engine)- Brake line filling

Water Removal- Insulation for Electrical

Transformers- Freeze Drying food and

pharmaceuticals

Rough Vacuum Applications

Heat Treatment (Furnaces)- Heating components under vacuum

to change mechanical properties

Vacuum Forming & Conveyance

Rough Vacuum ApplicationsSemiconductor Manufacturing

- Rough vacuum pumps are used for:• Initial pump down from atmosphere• Backing HV or UHV pumps• Wafer transfer and loadlock chambers.

VACUUM PUMP SELECTION

RANGE PUMP TYPE EXAMPLES

Rough Vacuum Atm - 10-3 Displacement

Pumps

Diaphragm PumpsRotary Vane PumpsOil-Free Scroll PumpsPiston PumpsScrew Pumps

High Vacuum 10-3 - 10-9 Displacement Pumps Capture Pumps

Diffusion PumpsTurbo Molecular PumpsCryo Pumps

Ultra High Vacuum < 10-10 Capture Pumps

Cryo Pumps, Ion PumpsSublimation Pumps

• ROUGH VACUUM pumps are most effective when gas is moving in VISCOUS FLOW

Displacement Pumps: Rough Vacuum

ROUGH VACUUM PUMPS

DIAPHRAGM PUMPS• Pressure differential created by deformation of elastic membrane allows gas

to enter the space above the piston• Inlet valve closes & exhaust valve opens (discharge to atmosphere or to inlet

of a second chamber)• Single and multi-stage models available

Limited base pressure Frequent replacement of

diaphragms (annual) Maintenance can be

complicated

Rough Vacuum: Oil-Sealed RVP

OIL-SEALED ROTARY VANE PUMPS• 1.5 m3/hr – 600 m3/hr• Molecules in VISCOUS FLOW enter the pump inlet• Gas is Isolated, Compressed (to above 760 Torr),

then Exhausted (or to 2nd stage)

Inlet Isolation Compression/Exhaust

Rough Vacuum: Oil-Free Scroll Pump

DRY SCROLL PUMPS (3 m3/hr – 35 m3/hr)• Compact, Oil-free pumps with high pump speed and low mTorr base pressure• Without OIL to achieve sealing, SCROLL PUMPS rely on (field replaceable)

TIP SEALS to achieve vacuum• Single and Dual Stage Versions available:

- Maintenance Simplicity vs Base Pressure!

15m3/hr • <50 dB15m3/hr• Hermetically Sealed

ROUGH VACUUM PUMPS

PISTON PUMPS • Piston pumps use coated PISTONS (eg.Teflon) and

CYLINDERS, and valving to achieve compression:- Inline, V-Twin, and Opposed Piston designs

Oil Free Initial Cost– Ultimate Vacuum– Maintenance

Oil Free Initial Cost Ultimate Vacuum– Maintenance

Displacement Pump Comparison

Diaphragm Pump

Oil-Sealed Rotary VanePump (RVP)

Oil-Free Scroll Pump

Oil FreePiston Pump

Oil Free Ultimate Vacuum Maintenance– Initial Cost

Initial Cost Ultimate Vacuum Oil

Oil Free Light Gases Audible Noise– Maintenance

RANGE GAUGE TYPE EXAMPLES

Rough Vacuum Atm - 10-3

Mechanical Deflection & Thermal Transfer Gauges

Capacitance ManometerThermocouple ConvectionPirani

High Vacuum 10-3 - 10-9 Mechanical Deflection

& Ionization Gauges

Capacitance ManometerHot Ion Gauge (BAG)Cold Cathode

Ultra High Vacuum < 10-10 Ionization Gauges &

Gas Analyzers

UHV Ionization GaugesIon Pump CurrentResidual Gas Analyzer (RGA)

Vacuum Measurement Technologies

- Different technologies are required to measure the vacuum pressure in different vacuum regions

Vacuum Measurement Technologies

GAUGE TECHNOLOGIES OVERLAP VACUUM REGIONS

Ultra High Vacuum High Vacuum Rough Vacuum

Mechanical Deflection Gauges

CAPACITANCE MANOMETER- DIAPHRAGM (between reference

and ‘test’ pressures) forms part of a capacitor circuit

- PRESSURE causes deflection which alters the capacitance) P C

- MOST ACCURATE and FASTEST RESPONSE gas independent gauge; Dynamic range ≈ 3.5

decades/gauge

Directly measure the physical force of gas molecules striking a surface

F1 F2

PT

Thermal Transfer Gauges

CONVECTION GAUGE- Maintain filament at constant T (above ambient): (P I)- Enhanced response time in viscous flow- Atm – < 1 x 10-3 Torr

THERMOCOUPLE GAUGE- Temperature of wire filament monitored at constant

Current (P T)- Slow response time; non linear above 2 - 5 Torr

Exploit the relationship between heat loss (through convection) and pressure

Thermal Transfer: Pirani Gauge

PIRANI GAUGEFilament (exposed to vacuum) forms one leg of a Wheatstone Bridge circuit;

• Loss of heat changes the resistance of the filament, unbalancing the bridge

• Voltage is applied to re-establish the balance: P Vapplied- Response is Gas Type Dependent (Gas

Correction factors required)- Extremely ‘non-linear’ above 1 Torr

Typical Pirani Gauge Response

Troubleshooting Rough Vacuum Systems

Time

Desorption

Pres

sure

(Tor

r) Volume

Diffusion

Pressure Decay

10+3

10-0

10-3

Troubleshooting Rough Vacuum Pumpdown

Monitoring the CHANGE in Pressure over Time can help to determine if there is a leak in the vacuum system

• A leak-tight system will display steadily decreasing slope until we reach the limits of the ROUGH VACUUM pumps

The slope of this line is proportional to the pumping speed

Time (min)0 5 15 2510 20 30

Pre

ssur

e (T

orr)

10+3

10+1

10-1

10-3

P

T Base Pressure

Troubleshooting Rough Vacuum Pumpdown

Time (min)0 5 15 2510 20 30

Pre

ssur

e (T

orr)

10+3

10+1

10-1

10-3

P

T

Monitoring the CHANGE in Pressure over Time can help to determine if there is a leak in the vacuum system

• A vacuum system with OUTGASSING issues will display a fairly constant rate of decrease in pressure over time

Base PressureOutgassing

Troubleshooting Rough Vacuum Pumpdown

Base Pressure

Time (min)0 5 15 2510 20 30

Pre

ssur

e (T

orr)

10+3

10+1

10-1

10-3

Real leak

Outgassing

Monitoring the CHANGE in Pressure over Time can help to determine if there is a leak in the vacuum system

• A vacuum system with a REAL LEAK will show a pressure change that drops, then flattens at the level of the leak

Rough Vacuum Troubleshooting: Rate of Rise TEST

Pres

sure

Time

TP

TP

Pre

ssur

e

Time

T

P

TPOutgassing/Virtual Leak:

- Rate of Rise (P/ T) DECREASES over time

Real Leak:- Rate of Rise (P/ T) remains

STEADY over time

Summary: Rough Vacuum Rough Vacuum Pumps (displacement pumps) require gas to be in

Viscous Flow to be effective. EFFECTIVE pumping speed approaches ZERO around 1 x 10-3 Torr.

Vacuum Pump choice depends on the importance to the user of:• Oil vs Oil-free Process• Base Pressure Requirements• Initial cost vs Lifetime Cost• Process Gas Limitations

Vacuum gauge selection depends on the accuracy required vs the cost. Gas dependent gauges require correction factor.

When approaching the lower limits of Rough Vacuum, OUTGASSING (Desorption and Diffusion) is the dominant factor (vs chamber volume)

Techniques for troubleshooting ROUGH VACUUM applications include Pumpdown Curves (P/T) and Rate-of-Rise or ‘Leak-Up’ Tests.

• Pump Speed at Operating Pressure• Maintenance Simplicity• Audible Noise

Vacuum Education Programs

For Information on Agilent’s Vacuum Technology Products and Services, please e-mail vpl-customercare@agilent.com or call 800-882 7426, and select option 3.

To learn about more Agilent Vacuum Technology Education programs, including• UHV Seminars at your institution• Scheduled multi-day classes in Vacuum Practice and Leak Detection• Custom multi-day classes at your site• Other custom training classes to fit your needs

Please e-mail Robin Arons (robin.arons@agilent.com), or call Customer Care at 800-882-7426 (Option 3) for more details on these programs

December 12, 2016

Confidentiality Label

29

Next Live Webinar: High Vacuum (Feb-7)

High Vacuum Webinar deals with the process of generating, measuring, and maintaining High Vacuum Pressure (10^-3 Torr to approx. 10^-8 Torr). ‘Roots’ type pumps (covering ‘Transition’ vacuum region) will also be discussed.Participants will learn about the benefits and drawbacks of different High Vacuum pump and Gauge technologies, and what to consider when constructing a vacuum system or troubleshooting leaks in the High Vacuum regime.

http://www.agilent.com/en-us/training-events/eseminars/vacuum

To Register, Visit: