HIGH VACUUM PUMPS - AIMCALDiffusion Pump Basics ... Boiler Design • Finned boiler provides larger heat transfer area & reduces temperature gradient between boiler plate & pump fluid

BASICS of MAINTENANCE and TROUBLESHOOTING of VACUUM

DIFFUSION PUMPS

Topics for DiscussionTopics for Discussion

•• Diffusion Pump BasicsDiffusion Pump Basics

•• MaintenanceMaintenance

•• TroubleshootingTroubleshooting


•• Diffusion Pump FundamentalsDiffusion Pump Fundamentals



Diffusion Pump

Diffusion Pump Fundamentals Diffusion Pump Fundamentals Typical pumping Typical pumping ““systemsystem””

QI

QO

SM

SD

PI

PO

Typical pumping system includes rough pumps, valves, gauging and vacuum hardware.

In this discussion we focus on the Diffusion Pump.

Diffusion Pump FundamentalsDiffusion Pump FundamentalsPrinciples of Operation Principles of Operation -- Basic Pump DesignBasic Pump Design

Diffusion Pump FundamentalsDiffusion Pump FundamentalsPrinciples of Operation Principles of Operation -- Momentum TransferMomentum Transfer

Diffusion Pump FundamentalsDiffusion Pump FundamentalsPrinciples of Operation Principles of Operation -- Momentum TransferMomentum Transfer

Cooling Coilson outside ofpump wall

Wall of Jet Assembly

Gas Molecules

Diffusion Pump FundamentalsDiffusion Pump FundamentalsBoiler DesignBoiler Design

•• Finned boiler provides larger Finned boiler provides larger heat transfer area & reduces heat transfer area & reduces temperature gradient between temperature gradient between boiler plate & pump fluid boiler plate & pump fluid

•• Prolongs fluid life due to lower Prolongs fluid life due to lower operating temperature, operating temperature, reduces thermal breakdownreduces thermal breakdown

Diffusion Pump Fundamentals Diffusion Pump Fundamentals Advantages of DPAdvantages of DP

•• Provides high throughput for handling large gas Provides high throughput for handling large gas loadsloads

•• Produces high pumping speed for long periods Produces high pumping speed for long periods with little attention & minimal maintenancewith little attention & minimal maintenance

•• Extremely dependable, reliable, & durable Extremely dependable, reliable, & durable •• Withstands improper operation w/o damageWithstands improper operation w/o damage•• Pumps all gases efficiently Pumps all gases efficiently •• Very economical per unit of pumping speedVery economical per unit of pumping speed

Diffusion Pump Fundamentals Diffusion Pump Fundamentals Diffusion Pumps are EconomicalDiffusion Pumps are Economical

Diffusion Pump Fundamentals Diffusion Pump Fundamentals Disadvantages of DPDisadvantages of DP’’ss

•• Requires water (or air) coolingRequires water (or air) cooling•• Must be installed verticallyMust be installed vertically•• Diffusion pump fluid disposalDiffusion pump fluid disposal•• Pump will operate outside intended Pump will operate outside intended

range without signaling operatorrange without signaling operator•• Backstreaming is always possibleBackstreaming is always possible





Diffusion Pump MaintenanceDiffusion Pump Maintenance

•• Diffusion Pumps require little maintenance.Diffusion Pumps require little maintenance.–– only proper air/water coolingonly proper air/water cooling–– electrical powerelectrical power–– charge of fluidcharge of fluid

•• In event of problem, should confirm electrical In event of problem, should confirm electrical power output, cooling water temperatures power output, cooling water temperatures (in/out), and fluid level & quality(in/out), and fluid level & quality

Diffusion Pump MaintenanceDiffusion Pump Maintenance•• DayDay--toto--day log of pump & system day log of pump & system

performance can be invaluable.performance can be invaluable.–– Indicates condition of pump.Indicates condition of pump.–– Record of variations that require corrective Record of variations that require corrective

action.action.

–– A simple log would include:A simple log would include:•• Cooling water Cooling water

–– TTinin and Tand Toutout

•• Electrical Electrical –– VoltageVoltage–– CurrentCurrent

•• Fluid: level and visual (color)Fluid: level and visual (color)

Diffusion Pump MaintenanceDiffusion Pump Maintenance

• Replace fluid periodically• Clean internal components• Remove oxidized fluid deposits• Re-assemble with new o-rings• Fill with new, clean fluid

Operational IssuesOperational IssuesDiffusion Pump MaintenanceDiffusion Pump Maintenance

•• Diffusion Pump FluidDiffusion Pump Fluid––Remove oxidized depositsRemove oxidized deposits––Check fluid level and color regularlyCheck fluid level and color regularly––Replace fluid periodicallyReplace fluid periodically


•• Clean internal pump components Clean internal pump components with appropriate solvents for the with appropriate solvents for the diffusion pump fluid being useddiffusion pump fluid being used

––Pump bodyPump body––Jet assemblyJet assembly


•• Keep boiler plate clean: Keep boiler plate clean:

a)a)Poor pumping performancePoor pumping performanceb)b)Fluid life can be shortenedFluid life can be shortened

Keeping boiler plate clean prevents cold spots Keeping boiler plate clean prevents cold spots and allows for a uniform heating of the fluidand allows for a uniform heating of the fluid


•• When reassembling pump:When reassembling pump:–– Install new oInstall new o--ringsrings–– Check for proper jet alignmentCheck for proper jet alignment–– Add new diffusion pump fluidAdd new diffusion pump fluid–– Inspect & verify heater wiringInspect & verify heater wiring

Operational IssuesOperational IssuesWaterWater--cooled Bafflescooled Baffles

•• Provides optically dense barrier Provides optically dense barrier •• Ideally provides high conductance & low Ideally provides high conductance & low

heightheight•• Suppresses rate of reSuppresses rate of re--evaporation of evaporation of

condensed or intercepted fluid condensed or intercepted fluid •• Reduces density of vapor in space Reduces density of vapor in space •• Retains 50% of pumping speedRetains 50% of pumping speed





TroubleshootingTroubleshootingForeline PressureForeline Pressure

If foreline pressure is to high:If foreline pressure is to high:

a)a)Will contaminate customer system.Will contaminate customer system.b)b)Will cause poor pumping performance.Will cause poor pumping performance.c)c) In extreme cases can cause explosion.In extreme cases can cause explosion.

This is most likely caused by a lack of This is most likely caused by a lack of understanding of what an acceptable understanding of what an acceptable MTFP is or operator error.MTFP is or operator error.

TroubleshootingTroubleshootingMaximum Tolerable Foreline PressureMaximum Tolerable Foreline Pressure

TroubleshootingTroubleshootingDefinition of BackstreamingDefinition of Backstreaming

•• Backstreaming:Backstreaming: ““migration of fluid beyond migration of fluid beyond pump inlet planepump inlet plane””

•• Leads to contamination of system & loss of Leads to contamination of system & loss of fluid from pumpfluid from pump

•• Backstreaming Rate:Backstreaming Rate: Pump manufacturers Pump manufacturers report backstreaming rate at inlet of pump report backstreaming rate at inlet of pump without inlet bafflewithout inlet baffle

•• Steady state collection rate at inlet plane (mg/cmSteady state collection rate at inlet plane (mg/cm22/min)/min)

•• System designers typically concerned with System designers typically concerned with backstreaming rate above pump baffles (not backstreaming rate above pump baffles (not the same)the same)

TroubleshootingTroubleshootingMost common causes of BackstreamingMost common causes of Backstreaming

•• Incorrect StartIncorrect Start--up/Shutup/Shut--down proceduresdown procedures•• Improper jet assembly alignmentImproper jet assembly alignment•• Extended transition pumping (crossover)Extended transition pumping (crossover)•• Exceeding maximum throughput (Q)Exceeding maximum throughput (Q)•• Exceeding Maximum Tolerable ForepressureExceeding Maximum Tolerable Forepressure•• High inlet pressures exceeding maximum Q High inlet pressures exceeding maximum Q

capacity for long periods of timecapacity for long periods of time

Troubleshooting Troubleshooting Minimizing BackstreamingMinimizing Backstreaming

•• Primary backstreaming can be prevented Primary backstreaming can be prevented via good pump design, use of cold caps & via good pump design, use of cold caps & baffles at room temperaturebaffles at room temperature

•• Cooled traps control backstreaming to such Cooled traps control backstreaming to such low level that contaminants from sources low level that contaminants from sources other than pump will predominateother than pump will predominate

•• Properly operated & protected systems can Properly operated & protected systems can be considered free of contamination from be considered free of contamination from pumping fluid for most applicationspumping fluid for most applications

Troubleshooting Troubleshooting Minimizing BackstreamingMinimizing Backstreaming

•• Use Good Vacuum PracticesUse Good Vacuum Practices•• Proper interlocks & protectionProper interlocks & protection•• Sufficient training to operating personnelSufficient training to operating personnel•• Use High Vacuum Valves & minimize Use High Vacuum Valves & minimize

diffusion pump operation at high pressuresdiffusion pump operation at high pressures•• Cold Caps & Halo BafflesCold Caps & Halo Baffles•• Liquid Nitrogen Cooled TrapsLiquid Nitrogen Cooled Traps

Troubleshooting Troubleshooting Common Problems Common Problems –– Heater Air GapHeater Air Gap

•• Between heating element and boiler Between heating element and boiler plate: plate:

a)a)NonNon--uniform heating of boiler plateuniform heating of boiler plateb)b)Shortened life of heater element because of Shortened life of heater element because of

over heatingover heating

Can be caused by the deformation of the boiler plate Can be caused by the deformation of the boiler plate due to low fluid leveldue to low fluid level

TroubleshootingTroubleshootingWater Leaks in SystemWater Leaks in System

a)a)Will destroy fluidWill destroy fluidb)b)Could cause explosion from rapidly Could cause explosion from rapidly

expanding gasexpanding gasc)c) Will cause poor pumping performanceWill cause poor pumping performance

Most likely caused by a leak in the cooling system Most likely caused by a leak in the cooling system of chamber or cooling required for application of chamber or cooling required for application (i.e. Cooling of target material)(i.e. Cooling of target material)

Troubleshooting Troubleshooting Common Problems Common Problems –– Cooling water FlowCooling water Flow

Low cooling water flow:Low cooling water flow:A)over heating the DP / explosion.A)over heating the DP / explosion.B)poor pumping performance.B)poor pumping performance.C)shortened fluid life.C)shortened fluid life.

Max. T of cooling water in: 80 deg. F.Max. T of cooling water in: 80 deg. F.Max. T of cooling water out: 130 deg. F.Max. T of cooling water out: 130 deg. F.Thermal cut off switch to heater element Thermal cut off switch to heater element

will open to protect DP.will open to protect DP.

Troubleshooting Troubleshooting Common Problems Common Problems –– Low DP Fluid LevelLow DP Fluid Level

a)a)Overheating of heater elementOverheating of heater elementb)b)Overheating of fluid / can ruin DPOverheating of fluid / can ruin DPc)c) Can melt aluminum DP stackCan melt aluminum DP stackd)d)Poor pumping performancePoor pumping performance

Note: Sight glass may be wrong as fluid volume Note: Sight glass may be wrong as fluid volume at DP may be consumed with sludge or at DP may be consumed with sludge or process materialprocess material

Thermal cut off switch to heater element will open Thermal cut off switch to heater element will open to protect DPto protect DP

Troubleshooting Troubleshooting System Open to AtmosphereSystem Open to Atmosphere

•• Opening chamber under vacuum.Opening chamber under vacuum.•• Not so common a problem.Not so common a problem.The resulting inThe resulting in--rush of gas to the chamber attempts to rush of gas to the chamber attempts to

lift the DP stack into the vacuum chamber and lift the DP stack into the vacuum chamber and damages the DP stack as well as deforms heater damages the DP stack as well as deforms heater plate.plate.

Be sure the chamber is at atmosphere if valve is open.Be sure the chamber is at atmosphere if valve is open.

Troubleshooting Troubleshooting Common Problems Common Problems –– Crossover PressureCrossover Pressure

•• If crossIf cross--over pressure is too high:over pressure is too high:

a)a) Will contaminate customer system.Will contaminate customer system.b)b) In extreme cases can degrade DP fluid.In extreme cases can degrade DP fluid.c)c) In extreme cases can cause explosion.In extreme cases can cause explosion.

This is most likely caused by a lack of acceptable This is most likely caused by a lack of acceptable crosscross--over pressure or operator error.over pressure or operator error.

Troubleshooting Troubleshooting Common Problems Common Problems –– Quick Cool LinesQuick Cool Lines

•• Water in quick cool lines during operationWater in quick cool lines during operation..Quick cool (option) intended to be an open circuit. Quick cool (option) intended to be an open circuit. All water MUST be out of DP quick cool lines before All water MUST be out of DP quick cool lines before

back into operation. back into operation.

Note:Note: quick cool lines should be shut off when DP is quick cool lines should be shut off when DP is not in use to prevent condensation build up.not in use to prevent condensation build up.

Thank YouThank You

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