Fundamentals of Vacuum Technology (1248463), страница 61
Текст из файла (страница 61)
In this case thepump should be sent in for repair or our customer service departmentshould be contacted.The roots pump may be switched on only after the roughing pump hasevacuated the vacuum vessel down to the cut-in pressure.Permissible cut-in pressure PE will depend on the reduction ratios of theroots pump as against the roughing pump and is calculated by dividing thepermissible pressure differential Æpmax by the compression ratio, reducedby the value of 1:p =Ek th =∆pmaxwherek th – 1Theoretical pumping speed for the roots pumpNominal pumping speed for the roughing pumpIf the pump is protected using a diaphragm-type pressure switch, then thepump will be switched on automatically. If a combination of roots pump androughing pump is to convey highly volatile substances such as liquids witha low boiling point, then it is advisable to use a roots pump which isequipped with an integral bypass line and a valve which will respond to apre-set pressure.
Example: Roots vacuum pumps RUVAC WAU / WSU.c) The measurement instrument is soiled (see Section 8.4.2).Potential sources of error when the pump no longer turns• Check the pump electrical supply.• The pump has stood for a long time containing contaminated orresinous oil.• The pump is colder than 10¡C and the oil is stiff. Heat the pump.• There is a mechanical error.
Please contact our customer servicedepartment.Oil exits at the shaftIf oil is discharged at the shaft, then the Seeger rotary shaft circlip in thedrive bearing will have to be inspected and possibly replaced. The designof the pumps makes it possible to replace this ring easily, following theoperating instructions provided with the unit.8.3.2 Roots pumpsRoots pumps from the RUVAC-WAU/WSU series, being equipped withbypass lines, can generally be switched on together with the forepump.
Thebypass protects these roots pumps against overloading.8.3.2.2Oil change, maintenance workUnder clean operating conditions the oil in the roots pump will be loadedonly as a result of the natural wear in the bearings and in the gearing. Wenevertheless recommend making the first oil change after about 500 hoursin service in order to remove any metal particles which might have beencreated by abrasion during the run-in period.
Otherwise it will be sufficientto change the oil every 3000 hours in operation. When extracting gasescontaining dust or where other contaminants are present, it will benecessary to change the oil more frequently. If the pumps have to run athigh ambient temperatures, then the oil in the sealing ring chamber shallalso be replaced at each oil change.We recommend using our specially formulated N 62 oil.8.3.2.1General operating instructions, installationand commissioningRoots pumps must be exactly level.
When attaching the pump it isnecessary to ensure that the pump is not under any tension or strainwhatsoever. Any strains in the pump casing caused by the connection linesshall be avoided. Any strain to which the pump is subjected will endangerthe pump since the clearances inside the roots pump are very small.Roots pumps are connected to the line power supply via the motor terminalUnder ÒdirtyÓ operating conditions it is possible for dust deposits to form aÒcrustÓ in the pump chamber.
These contaminants will deposit in part in thepumping chamber and in part on the pumpÕs impellers. They may beremoved, once the two connection lines have been detached, either byblowing out the system with dry compressed air or by rinsing with a suitablecleaning agent, such as petroleum ether (naphtha).The oil in the roots pump will then have to be changed. The rotor may beturned only by hand during cleaning since, due to the high speed when the142HomeInstructions for equipment operationmotor is running, the deposits could damage the pump as they dislodgefrom the surfaces.8.3.3 Turbomolecular pumpsGrime which cannot be eliminated by washing can be removedmechanically using a wire brush, metallic scrubber or scraper.8.3.3.1Important!The dislodged residues may not remain in the pump chamber. Aftercleaning is completed check the pump for operability by slowly turning theimpellers by hand.
There may be no resistance to rotation. It is generallynot necessary to dismantle the roots pump. If this should nevertheless berequired due to heavy soiling, then it is highly advisable to have this doneby the manufacturer.8.3.2.3Actions in case of operational disturbances1. Pump becomes too warm: (maximum operating temperature100 to 115 ¡C)Possible causes:• Overloading: Excessive heat of compression due to an excessivelyhigh pressure ratio.
Check the pressure value adjustments and thetightness of the vacuum chamber!• Incorrect clearances: The distances between the rotors and thehousings have been narrowed due to dirt or mechanical strain.• Soiled bearings: Excessive friction in the bearings• Improper oil level: If the oil level is too high, the gears will touch the oil,causing friction resistance. Where the oil level is too low the system willnot be lubricated.• Incorrect oil type: An SAE 30 grade oil must be used for the pump.2. Excessive power consumption: All the factors which can lead toelevated temperatures can also cause excessisve amounts of power tobe drawn. The motor is defective if excessive power requirements arenot accompanied by a rise in the temperature at the pump.3.
Oiling at the pump chamber:Possible causes:• Oil level too high: Oil is subjected to excessive thermal loading. Oilfoam is swept along.• Oil mixed with the product: Azeotropic degasification of the oil.• Pump leaking: Air ingress through the oil drain or filler screw will causea large stream of air and conveyance of oil into the pumping chamber.4.
Abnormal running noises:Possible causes:• Grime at the impeller• Bearing or gearing damage• Impellers are touching the housingIn the case of bearing or gearing damage or where the impeller scrapes thehousing the pump should be repaired only by the manufacturer.General operating instructionsIn spite of the relatively large gap between the pump rotor and the stator,the turbomolecular pumps should be protected against foreign objectsentering through the intake port.
It is for this reason that the pump shouldnever be operated without the supplied wire-mesh splinter guard. Inaddition, sharp shock to the pump when running and sudden changes inattitude are to be avoided.Over and above this, and particularly for the larger types with long rotorblades, airing the pump to atmospheric pressure while the impellers arerotating may be done only when observing exactly the rules given in theoperating instructions. Under certain circumstances it is possible to operateturbomolecular pumps under exceptional conditions.The turbomolecular pump may, for example, be used unprotected insidemagnetic fields if the magnetic induction at the surface of the pump casingdoes not exceed B = 3 á 10-3 T when radially impinging and B = 15 á 10-3 Tat axial impingement.In a radioactive environment standard turbomolecular pumps can be usedwithout hazard at dose rates of from 104 to 105 rad. If higher dose rates areencountered, then certain materials in the pump can be modified in order towithstand the greater loading.
The electronic frequency converters in suchcases are to be set up outside the radioactive areas since the semiconductors used inside them can tolerate a dose rate of only about 103 rad.The use of motor-driven frequency converters which can withstand up to108 rad represents another option.Roughing (backing) pumps are required for the operation of turbomolecularpumps. Depending on the size of the vessel to be evacuated, theturbomolecular pumps and forepumps may be switched on simultaneously.If the time required to pump the vessel down to about 1 mbar using theparticular fore-pump is longer than the run-up time for the pump (seeoperating instructions), then it is advisable to delay switching on theturbomolecular pump.
Bypass lines are advisable when usingturbomolecular pumps in systems set up for batch (cyclical) operations inorder to save the run-up time for the pump. Opening the high vacuum valveis not dangerous at pressures of about 10-1 mbar.8.3.3.2MaintenanceTurbomolecular pumps and frequency converters are nearly maintenancefree. In the case of oil-lubricated pumps it is necessary to replace thebearing lubricant at certain intervals (between 1500 and 2500 hours inoperation, depending on the type). This is not required in the case ofgrease-lubricated pumps (lifetime lubrication). If it should becomenecessary to clean the pumpÕs turbine unit, then this can easily be done bythe customer, observing the procedures described in the operatinginstructions.143HomeInstructions for equipment operation8.3.4 Diffusion and vapor-jet vacuumpumps8.3.4.1Changing the pump fluid and cleaning thepumpChanging the pump fluid is always necessary whenever the pump no longerachieves the required ultimate vacuum or when its pumping speed falls off.The service life of the pump fluid will as a rule come to several weeks ormonths Ð or even years Ð and will depend largely on the operatingconditions for the pump.
It is reduced by frequent pumping at highpressures, by exposure to aggressive vapors and by air ingress of longerduration (this does not apply to silicone oil and mercury).In the case of oil diffusion and vapor-jet pumps the danger presented to thepump fluid where there is air ingress with the pump hot is oftenoverestimated. Where air ingress (up to atmospheric pressure) isencountered only occasionally and for short periods of time then silicone oilwill not be attacked at all and the DIFFELEN pump fluid will only barely beaffected.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
