Fundamentals of Vacuum Technology (1248463), страница 60
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during impregnation) it may be necessary to changethe oil daily. The oil will have to be replaced when its original light browncolor, has turned dark brown or black due to ageing or has become cloudybecause liquid (such as water) has entered the pump. An oil change is alsonecessary when flakes form in corrosion protection oil, indicating that thecorrosion protection agent is exhausted.Changing the oilThe oil change should always be carried out with the pump switched off butat operating temperature. The oil drain (or fill) opening provided for eachpump is to be used for this purpose. Where the pump is more seriouslycontaminated, then it should be cleaned.
The applicable operating instructions are to be observed in this case.Pumping speed [m3 á hÐ1]¸8.3.1.2Intake pressure [mbar]Example: Oil losses for a TRIVAC S 16 A at pressure of 1 mbar:a) Without gas ballast: in accordance with the pumping speed curve S = 15 m3 / h; accordingto diagram: oil loss = 0.03 cm3 / h (line a)b) With gas ballast: S = 9 m3/h at 1 mbar; oil loss = 0.018 cm3 / h (line b1), plus additionalloss due to gas ballast quantity (0.1 times the 1.6 m3 / h rated pumping speed); that is: Chart onthe horizontal line b2 up to atmospheric pressure: additional loss: 3 cm3 / h (diagonal line).Overall loss during gas ballast operation 0.018 + 3 = 3.018 cm3 / h.Fig.
8.1Oil loss for oil-sealed pumps (referenced to an approximate maximum value of 2 cm3oil loss per cubic meter of air drawn in [STP])Selection of the pump oil when handlingaggressive vaporsIf corrosive vapors (e.g. the vapors formed by acids) are to be pumped,then a PROTELEN¨ corrosion protection oil should be used in place of thenormal pump oil (N 62). These types of vapors will then react with the basic(alkaline) corrosion protection agent in the oil. The continuous neutralizationreactions will exhaust the corrosion protection agent at a rate depending onthe quantity and acidity of the vapors. The oil will have to be changed morefrequently, in accordance with these factors.
Corrosion protection oils areeither very hygroscopic or they easily form emulsions with water.Consequently a pump which is filled with corrosion protection oil will absorbmoisture from the air if it is out of service for an extended period of time. Inno case should one ever use a pump filled with corrosion protection oil inorder to pump water vapor since the lubricating and corrosion inhibitionproperties of the oil would be adversely affected. Once the oil has absorbedwater it will no longer be possible for such pumps to achieve the ultimatepressures which would be the case with fresh corrosion protection oil orstandard pump oil (N 62). Oil-filled pumps should, under normal operatingcon-ditions, not be filled with corrosion protection oil.
N 62 oil is preferredwhen pumping air, water vapor and non-corrosive organic vapors in so faras there is positive protection against the vapors condensing inside thepump.140HomeInstructions for equipment operation8.3.1.3Measures when pumping various chemicalsubstancesThis discussion cannot provide exhaustive coverage of the many and variedapplication fields for oil-filled vacuum pumps in the chemicals industry.
Ourmany years of experience with the most difficult of chemicals applicationscan be used to solve your particular problems. Three aspects should,however, be mentioned briefly: pumping explosive gas mixes, condensablevapors, and corrosive vapors and gases.Explosion protectionApplicable safety and environmental protection regulations shall beobserved when planning and engineering vacuum systems. The operatormust be familiar with the substances which the system will be pumping andtake into account not only normal operating conditions but also abnormalsituations, operating outside normal parameters. The most important aids toavoiding explosive mixtures are Ð in addition to inertization by addingprotective gases Ð maintaining the explosion limit values with the aid ofcondensers, adsorption traps and gas scrubbers.Protection against condensationLEYBOLD pumps offer three options for keeping vapors from condensing inthe pumps:• The gas ballast principle (See Fig.
2.14). This increases considerablythe amount of vapor which the pump can tolerate.• Increased pump temperature. The rugged design of our pumps makes itpossible to run them at temperatures of up to 120 ¡C. Thus thetolerance for pure water vapor, for example, will rise by a factor of fivewhen compared with normal gas ballast operation.• Using vacuum condensers (see Section 2.15). These act as selectivepumps and should be sized so that the downstream gas ballast pumpwill not receive more vapor than the amount corresponding to theappropriate vapor tolerance.Corrosion protectionOil-sealed pumps are already quite satisfactorily protected against corrosiondue to the oil film which will be present on all the component surfaces.Corrosion is defined here as the electrochemical dissolution of metals, i.e.the release of electrons by the metal atom and their acceptance by theoxidation agent (corrosive gas).
A metal atom which is susceptible tocorrosion must therefore be exposed to an active atom of the oxidationagent.This makes clear how the oil-sealed pump is protected against corrosion;the concentration of the oxidation agent in the oil is negligible and thus theopportunity for the metal to release electrons is equally small. This alsomakes it clear that the use of so-called Ònon-rustingÓ or ÒstainlessÓ steelsdoes not make sense since oxidation is necessary for the passivation ofthese steels, in order to reach the so-called passive region for these steelcompounds. The critical passivation current density will normally not appearin oil-sealed pumps.a) AcidsOur pumps are fundamentally suited to pumping acids. In special situationsproblems with the oil and with auxiliary equipment attached at the intakeand/or discharge end may occur.
Our engineers in Cologne are available toassist in solving such problems.b) AnhydridesCO (carbon monoxide) is a strong reducing agent. When CO is beingpumped it is therefore important that air not be used as the gas ballast butrather that inert gases be used at the very outside (e.g. Ar or N2). Inert gasballast should also be used when pumping SO2, SO3, and H2S. A corrosioninhibiting oil is also to be used when handling these three anhydrides.Carbon dioxide (CO2) can be pumped without making any specialarrangements.c) Alkaline solutionsNormal N 62 pump oil is to be used to pump basic (alkaline) solutions.Sodium hydroxide and caustic potash solutions should not be pumped intheir concentrated form.
Ammonia is highly amenable to pumping with thegas ballast valve closed. Alkaline organic media such as methylamine anddimethylamine can also be pumped satisfactorily, but with the gas ballastvalve open.d) Elementary gasesPumping nitrogen and inert gases requires no special measures.When handling hydrogen it is necessary to make note of the hazard ofcreating an explosive mixture. The gas ballast valve may in no case beopened when dealing with hydrogen. The motors driving the pumps mustbe of explosion-proof design.Oxygen: Particular caution is required when pumping pure oxygen!Specially formulated pump oils must be used for this purpose.
We cansupply these, accompanied by an approval certificate issued by the GermanFederal Materials Testing Authority (BAM), following consultation.e) AlkanesThe low molecular weight alkanes such as methane and butane can bepumped with the gas ballast valve closed or using inert gas as the gasballast and/or at increased temperature of the pump. But important ÐIncreased explosion hazard!f) AlcoholsOnce operating temperature has been reached, methanol and ethanol canbe extracted without using gas ballast (N 62 pump oil). To pump highermolecular weight alcohols (e.g. butanol) the gas ballast valve will have tobe opened or other protective measures will have to be implemented toprevent condensation.g) SolventsAcetone: Can be extracted without difficulty; wait until normal operatingtemperature is reached.Benzene: Caution Ð vapors are highly flammable.
Ultimate pressure isdegraded by dilution of the pump oil. Mixtures of air and benzene areexplosive and flammable. Work without a gas ballast! Inert gases maypossibly be used as ballast gas.Carbon tetrachloride and trichlorethylene: Amenable to pumping; nonflammable and non-explosive but will be dissolved in oil and thus increasethe ultimate pressure; wait until normal operating temperature is achieved.141HomeInstructions for equipment operationKeep the gas ballast open when pumping carbon tet and other nonflammable solvents.
Use N 62 pump oil.strip; a motor protection switch (overload/ overheating) shall be provided asrequired by local codes.Toluene: Pump through the low-temperature baffle and without gas ballast.Use inert gas, not air, as the gas ballast.The direction of motor rotation shall be checked with the intake and outletports open prior to installing the pump. The drive shaft, seen from the motorend, must rotate counter-clockwise.
Note the arrow on the motor indicatingthe direction of rotation! If the roots pump runs in the wrong direction, thenit is reversed by interchanging two of the phases at the motor connectioncord.8.3.1.4Operating defects while pumping with gasballast – Potential sources of error wherethe required ultimate pressure is notachieveda) The pump oil is contaminated (particularly with dissolved vapors). Checkthe color and properties.
Remedy: Allow the pump to run for anextended period of time with the vacuum vessel isolated and the gasballast valve open. In case of heavy contamination an oil change isadvisable. The pump should never be allowed to stand for a longerperiod of time when it contains contaminated oil.b) The sliding components in the pump are worn or damaged. Under cleanconditions our pumps can run for many years without any particularmainte-nance effort. Where the pump has been allowed to run for alonger period of time with dirty oil, however, the bearings and the gatevalves may exhibit mechanical damage. This must always be assumedwhen the pump no longer achieves the ultimate pressure specified inthe catalog even though the oil has been changed.
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