Diffusion Vacuum Pump




Introduction: Diffusion Vacuum Pump

About: Professional work in various electrical and mechanical fields, obscure sense of humour and typically willing to help... Currently under contract designing environmental monitoring equipment.

Please look up the definition of a Diffusion Vacuum Pump before continuing!

This pump is made from readily available materials and has been shown to achieve a .022 TORR vacuum!!!!

Use extreme caution when working with vacuum

This pump needs a "Roughing" pump to get down to a near vacuum then it will work as described.
No a refrigerator compressor will not work as a "Roughing" Pump for this
No a vacuum cleaner will not work either!

You will need a refrigeration service type pump for the "Roughing" of the vacuum.

Yes you may have to go to IKEA to get some of the parts!

Step 1: Materials

You will need a stainless steel tube (I used an exhaust pipe section)
Some 1/4 inch copper tube and
stainless steel flat sections.

I found that the local scrap yard had lots of stainless steel parts. Selecting the right few took a couple of trips.

You will also need to know how to braze. I used stainless brazing rod for joining all parts.

I used a stainless 2.75 od exhaust pipe adapter for the body. Some scrap stainless flats for the ends.

All cutting was done with a Dremel and cut-off abrasive wheel.

Several Ikea stainless cups were sacrificed for this build!

Step 2: Lower End

The base was a scrap cut stainless round. the edged were smoothed and a 10x32 nut was brazed in the center.
This was then brazed to the center of the exhaust pipe.

a 1/2 inch hole was drilled into the exhaust pipe for a vacuum port. This was about 1 inch from the bottom edge.

Step 3: Vacuum Port and Braze Together

Add a vacuum port that is at lease 1/2 inch in diameter and up and away from the body of the pump.

I used a 1/2 inch tube cut an brazed together at a 45 degree point then brazed tot he body of the pump.

It is important to make sure that there is no leaks!!!

I tested this by blocking the vacuum port then inverting the pump body and drawing a deep vacuum on my vacuum table. I got down to 150 microns which was a really good indication that there were no leaks.

Step 4: The Active Cones!

I used some Ikea stainless glasses and dollar store spice jars for the internal cone structure.

All were cut, drilled and welded as in the photos.

The spice jars were cut off and brazed together.

The ikea glasses were drilled and cut as shown in the pics.

All cone assemblies were to fit inside of the the outer exhaust tube. No parts were to extend outside of the tube.

Step 5: Silicone Oil

Getting the oil for proper pump operation is actually quite simple..

It can be refined from spray lube or harvested from a photocopier (fuser oil)

It can be purchased.

Silicone oil is expensive but seems to be the oil of choice for these pumps.

It is non-flammable and non-reactive. Plus is works great!

I harvested fro a spray lube by first spraying the entire contents into a jar. I heated and vacuumed the jar until I had pure silicone oil. It took quite a while and i did go through quite a bit of vacuum pump oil but the end oil works great!. Do not heat it in atmosphere as it will burn and not work properly in the future!

Step 6: Finish the Top

I used a section of stainless steel for the top.

The opening was marked then perimeter drilled then cut and finished with a Dremel and a half round file.

The opening had to have the same inner diameter as the the exhaust pipe.

All slag from the brazing was then cleaned off with a wire brush.

The end plate was then brazed to the top of the pump assemble.

I brazed 2 opposite sides than all the way around the edge to make a complete seal.

Step 7: Test the Pump

I used a jam jar with a silicone baking mat to test the final seal.

The inner cones were bolted into place then the oil was added. The assembly was placed into a shop vise and I used a propane torch to heat the bottom of the pump. In the future a stove element will be used but this was just a test..

I attached the pump to the vacuum port then ran the pump for about a 1/2 hour. I was able to get a vacuum of around 130 microns.

With no water cooling and constant heating got the vacuum down to less than 22 microns. This is far deeper than my refrigeration pump has ever gone!!! I need to water cool the pump body to get some extreme vacuums!

That is 0.022 TORR.. Let the games begin!

I will be making extensive use of this pump in the near future for some amazing instructables!

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    Noman hameed
    Noman hameed

    6 years ago

    Dear bro!

    Diffusion pump oil is not available
    in my country and also I can't bear the expense in importing of DP oil.
    Here in my country side there are a lot of silicone base oil to which i
    can use as a low vapor pressure oil, but think is I really dont know
    which staff has to use.in this purpose. Can you do me a favor?..... If
    you can help me out in this project of making oil for diffusion pump.
    And also i need help in making diffusion pump.


    8 years ago on Introduction

    Thank you...I finally understand how a diffusion pump works. Been looking at these awhile and scratching my head. You might link to this swf with an animated cross section of how it works on a molecular level.



    8 years ago on Introduction

    I'm curious what sort of torch you are using? As well as the rough total amount you ended up spending? Thanks! Very cool!


    Reply 8 years ago on Introduction

    The torch is a Smith Little Torch. Quite small for this job but I used what I had.

    The Stainless metal was $1 per pound at my local scrap yard "Federal Metals Calgary". The retail parts were under $10 and the tubing was purchased over 10 years ago for about $20.


    9 years ago on Introduction

    I'm a bit lost. Some background, a working principle and a schematic would make this a great instructable. Also, could you explain a bit more about the construction? For example in step 6, where does the copper coil come from? It's just there all of a sudden without explanation. Thanks.


    Reply 9 years ago on Introduction

    Sorry about that. I got in the zone with the build. The copper tube is a gravity feed cooling apparatus. Wrap 3-4 coils of copper tube around the body of the pump. Braze this tot he body. Water is gravity fed in a steady drip to facilitate cooling of the pump body and allow the pump to cool the heated oil.


    9 years ago on Step 7

    You win a follower with this pump i am making my own but i have a question can i use 2 fridge compresors in series as a mechanical pum i know that the ideal pump is the rotary vanes one, but here in Mexico they are really expensive i know that one can get a vacuum of 100mbar


    10 years ago on Introduction

    Awesome project!

    Surely you can aluminize using this vaccum pump, isn't?


    Reply 10 years ago on Introduction

    I envy you a bit... Is there something like good envy?


    Reply 10 years ago on Introduction

    Yep, called "admiration" and "inspiration".