Solvents for difussion pump oils

[Alberto Sanchez]

Hello.

What is the best solvent to cleaning a oil difussion pump after using regular Roughing pump oil?

And What is the best solvent to cleaning a oil difussion pump after using DOW CORNING 704?

Also, do I need to apply a second/final wash to remove the first solvent, likeisopropyl alcohol or acetone?

I ask for solvents because it makes sense to me, maybe is water and detergent or somethin, I have no Idea.

thank you

Best regards

[Dennis P Brown]

Never use detergents and water is best avoided. The former because trace amounts will contaminate your system and the later requires a bake out under vacuum.

No need to clean a good DP unless you just bought it and have no idea what its state is; assume toxic materials could have contaminated it. I.e. use gloves and be careful of the waste.

Warm the item to be cleaned and be certain all easy to eliminate trace oil is removed (lint free cloths to clean it; these should wipe clean at some point.)

Then warm acetone (not hot*) is SOP for many oil based systems to be cleaned like a DP. Absolute alcohol (unlikely now to be available) is good as a second rinse. Isopropyl is an alternative.

If the old pump has not been burnt, a gentle rubbing (using proper gloves) and a lint free cloth should suffice during the acetone/alcohol treatments.

Then a bake out under vacuum before adding new oil. Do the jets separately using the same chemicals/process and leave them in the air to dry.

If available (and done outside; avoid breathing, wear safety googles) an initial liquid cleaning using TCA on the entire assembly to remove trace oils can be done.

Dispose of all used organics/oil properly. I tend to let waste organic liquids evaporate. Do not pour these substances down public drain systems.

* Organic liquids have serious flash points one does not want to reach.

[Alberto Sanchez]

Thank you for your answer.

What SOP ant TCA stand for?

[Dennis P Brown]

Sorry - sloppy writing on my part.

SOP: Standard Operating Procedures

TCA is the abbreviation for a very powerful and hazardous organic solvent. If you do not know what it stands for its best you not learn nor buy it/use it. Disposal can be very difficult, and besides, it dissolves most types of safety gloves. Its bad news if you get it on yourself; unlike acetone (through best to avoid getting that on yourself or breathing its vapors.)

[JoeBallantyne]

Per Google, TCA stands for trichloroethane or tetrachloroethane.

Trichloroethane is longer made in the USA as it depletes the ozone layer.

Joe.

[Rich Gorski]

Just to avoid confusion, TCA stands for tricloroacetic acid and the abbreviation for tricloroethelyne or tricloroethane is TCE. Its the ethane version is the one that destroys the ozone layer. Ethylene version does not according to Google.

Although the solvent TCE is no longer manufactured in the US you can still purchase it here. Its available on Amazon. If you decide to use it Google says nitrile gloves are fine and are available everywhere, Walgreens, Target, OSCO etc.

Rich G.

[JoeBallantyne]

Trichloroethene and trichloroethane are not the same thing.

Trichloroethene - TCE - is the IUPAC name for trichloroethylene or ethylene trichloride.
Trichloroethane - TCA - which per Wikipedia trichloroethane (C2H3Cl3) may refer to either of two isomeric chemical compounds:

1,1,1-Trichloroethane (methyl chloroform, CCl3CH3)
1,1,2-Trichloroethane (vinyl trichloride, CHCl2CH2Cl).

According to Google TCA can stand for trichloroethane, tetrachloroethane, or trichloroacetic acid. Each a different chemical from the others.

The answer you get from google depends on what you ask it.

If you ask

what is TCA solvent

You get TCA solvent could refer to 1,1,1-trichloroethane, tetrachloroethane, or trichloroacetic acid, which are all chemicals with various uses:

If you ask

what chemical is TCA

You get TCA stands for Trichloroacetic Acid. It's a chemical commonly used in medium-depth chemical peels to remove the top layer of skin, treating issues like wrinkles, acne scars, and sun damage.

I suppose we could just ask which solvent Dr. Brown was referring to when he used the TCA acronym. Which he then declined to identify further. I doubt it was Trichloroacetic acid.

Joe.

[Rich Gorski]

I'm sure Dennis is referring to the common solvent/degreaser trichloroethylene more commonly abbreviated TCE not TCA. It's still in common use in the US. I'm sure he was not referring to the acid (more commonly abbreviated TCA) is a used as a skin treatment. He was also not referring to tricloroethane (also abbreviated TCE) which is hard to find and generally phased out for use in the US.

Rich G.

[Alberto Sanchez]

Thank you
My double question is because I have made a homemade diffusion pump. In my first try I'd like to use regular roughing pump oil. And if it works, replace it with Dow Corning 704.

Nevertheless. In case of accident and air gets into the pump while is hot, Dow Corning 704 also spoils or remains OK?

[Dennis P Brown]

Roughing pump oil is not good as a diffusion pump oil due to its vapor pressure issues. It will contaminate your entire system and it also requires a rather high temp to get the 'jet' action further causing issues due to it viscosity. As for burning oil - yes, any oil can be burned to carbon w/o proper cooling and correct heater current. That is why most people use commercial units - these issues are addressed by people who understand the dynamics. Building a DP compared to the low cost units often on ebay seems like a lot of trouble but certainly can be done. Using the correct oil makes more sense and yes, those oils are expensive but for a reason - they work properly and do not contaminate a vacuum system when heated.

[Alberto Sanchez]

Thank you.

I see. The problem is, I don´t want to risk the little ammount of DC 704 in the firs try of the vacuum pump. I have check the pump with pressure and with vacuum, but I want to be sure

[Daniel Harrer]

I cannot say anything about diffusion pumps, but a 50-50 mixture of acetone and toluene is a strong solvent which is used to dissolve dirty oil. It depends on the materials if it is suitable. Unlike TCA/TCE it is relatively harmless.

As with any volatile solvent: good ventilation and/or a gas mask is strongly advised.

[Alberto Sanchez]

Thank you

[John Futter]

DCM Dichloromethane or methylene chloride does a good job but it takes time
it is also a greenhouse gas/solvent so you need to cover it with water --DCM is heavier than water so it will not evaporate if covered.
when I say it takes time--days/ weeks

[Alberto Sanchez]

Thank you.

This time I have double check everithing, and I have welded the pump using TIG instead silver brazing. I have tried under small pressure (2 bars) and under vacuum and no leaks. All the parts boiled for 30 minutes with dishwasher soap, 15 minutes boiling in tap water and 15 minutes boling in purified water. And after all of that, 1 hour in isopropyl alcohol.

I´ll make a try with the DC 704. The question is, if I have a leak while is boiling and shut doen the heat element, lets say it takes 10 minutes to cool down (i have put a small fan to cool it when I fihish) In that case, tue oil will be ruined?

[Rich Gorski]

Alberto,

Yes, it is possible that the oil could be ruined. If enough oxygen gets into the system from a leak the oil could burn and form combustion products which will contaminate the remaining oil. However it would take a major leak for a burning condition to materialize. If you are unsure of your vacuum system test it with oil but without heat first and make sure you don't have any leaks. If all looks good then start bringing the oil temperature up to the operating point.

Also note that the oil temperature for diff pumps is around 225C. This is also the near flash point for diff pump oil.

Don't forget to water cool the top of the pump so the oil vapor has something cold to condense on.

Rich G.

[Alberto Sanchez]

AHH ok. So the oil is ruined only if it stars to burn right? I mean, if is burn, I'll be able to see that because it will change the color and the smell right?

Thank for your answer and advice. Yes the pump is water cooled