what is the property of vacuum oil (used in vacuum pump etc) is there any downloadable material ? if i use same viscosity grade oil in place of vacuum oil what will be effect??
The maximum vacuum level is determined by the lowest vapour pressure of any substance present at any given temperature.
Using a more volatile oil will mean a lower vacuum is achieved.
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we are using a root pump befor liquid ring pump to boost the vapour medium now problem is that suddnly vacuum changed from 0.00 torr to 13 torr now what may be proabable reason. we took following action
1)complete line cleanig for any chocking
2)leakage checked there is no lekage
after doing all above activity we did not found any improvement
then we change root pump(twin lobe type) both side lube oil(fresh oil P3) as we found temp is high(80 Deg) on both side after that we again started the system then we found 0.00 torr again, now i am not able to uderstand how it happend
we tested the lube oil sample(used one) on our laboratry we found 10% mixing of glycol vapour(pumping medium) on the lub oil
now i fully confused how vacuum break from 0.0 torr to 10.0 torr
is thr any link with lube oil ??
or there are some othe reason?
mixing of glycol indicate there may be lekage from sealing but now how it is working well
<vacuum changed from 0.00 torr to 13 torr now what may be proabable reason>
The maximum vacuum level is determined by the lowest vapour pressure of any substance present at any given temperature.
Using a more volatile oil will mean a lower vacuum is achieved.
<we found 10% mixing of glycol vapour(pumping medium) on the lub oil>
Bingo!
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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
High vacuum oils are very expensive as they are fractionated with purging gasses to eliminate any smaller molecular weight molecules. These gasses are then removed to give you a vacuum oil with low torr.
Open the gas ballast valve of the pump and you will get rid of the problems.
In any vacuum pump that is pumping condensable gas (liquid in its evaporated status)
you will have condensation at the higher pressure side if pressure is high enough and temperature is low enough.
To prevent mixing of the condensing droplets with the vacuum oil there is the gas ballast valve: if opened a small amount of air (or other gas if air is not suitable) is fed into the condensing vapor and sweeping the condensed fog out together with the air.
(You will spoil your pump with corrosion if water is accumulating in the oil!)
I would recommend to use nitrogen or other inert gas as gas ballast as you may get an explosive mixture by any burnable (glycol) condensed fog in air. And get a cooler and a filter at the exhaust, the fumes may be very toxic.
we are using Nitrogen for blasting purpose but we have fully stoped the flow because the moment we start flow vacuum break start however we try throttling from minimum flow , therefor we are not using any gas for blasting
i know this gas is used to prevent the vapour flow toward bearing/oil
but my problem is that how vacuum level automatically improved while i changed lube oil.
is there any link with lube oil if yes then how or there was some other reason, what may be possible reason??
At the risk of sounding redundant, you should know that any oil
contamination with a higher vapor pressure than the
oil itself, will limit the lower pumping pressure to
the vapor pressure of the contaminant. This applies to water, glycol,
or any other contamination. Replace the pump oil with uncontaminated
lube, and the pressure goes down to where it should be.
Exactly. If you use some sort of lube oil then the light fractions and probably some of the additives are going to "boil" when you try to pull a vacuum. So you won't be able to get a good vacuum, only to the level where you start to boil the lightest fractions. Then you've coated the whole system with junk.
As welderman said, you're going to have to empty and clean out the vacuum pump and add the correct vacuum oil back into the sump.
Doing anything else is just a waste of time. There are no shortcuts for this one.
you did contaminate your oil with the pumped liquid (pumped as gas but condensed to a solution of organic compounds in oil.
This condensate will reevaporate at low pressure and this is limiting your pressure.
Other comments did state that the vapor pressure is the limit: the vapor pressure of the liquid that is dissolved in your oil.
With new oil a good pressure can be attained until you have again organic stuff (with high vapor pressure) dissolved. This will happen after some time of pumping unless you use permanently the gasballast. This is not the same as the barrier gas that is used to protect the bearing assembly from being contaminated!
Gasballast has to be used permanently if pumping condensible gas. This is to prevent condensated droplets to be smeared around the inner surfaces and reevaporate at low pressure. The condensated droplets will flow out with a stream of the added gasballast.
If your roots pump does not have a valve to be opened or a connection for gasballastinput then it is advisable to add a dosing valve (a small leak can be used too, made from a capillary tube) at the high vacuum side.
Use the barrier gas in addition because the bearing lubricant would not like your pumped whatever to condensate - only the pump repair shop likes this.
best would be to ask the pump manufacturer, they should know.
Second best would be a trial and error method: connect a needle valve to the low pressure side of your pump. The needle valve should be able to let in nitrogen at a rate that is in the region of (0.001 to 1) x gas flow rate of pumped (condensable) stuff.
Let in nitrogen, start at a medium rate of nitrogen gasballast and check if pressure and flow stays good for an extended period.
If yes you can lower the rate of gas ballast flow (but be cautious) if no you should let allow for more gasballast flow.
If no needle valve is at hand this can be done by any small leak but this may require some tricks. We tryed using a long very small capillary tube and in another trial a metallic plate with a very fine hole that we punched with the tip of a needle into aluminum or copper foil 0.2mm thick. We let not pass the shaft of the needle trough the foil but stopped it with an underlying steel plate so that the hole was really very fine. But may be your flow rate is requiring something totally different in cross section.
And: get a handbook on high vacuum engineering, there are more useful "how to ..."
Vacuum Oil and Grease
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