Fusor Forums

Wow....just simply fantastic. The craftsmanship exemplified thus far is astonishing! I look forward to seeing how it works.

-Chad

The boiler section of the pump has been the easiest part so far. It took about 5 minutes to setup and braze a 1/4" SS bolt to the bottom of the pump body and another 10 minutes to cut up a vegetable can from the pantry and then put some holes and grommets in it. The trimmed can was used like a cookie cutter to make the Fiberfrax insulation pieces. The rope heater was wrapped flat against the bottom of the pump body and compressed into place by the lid from the can, which also had a hole in the center. This formed a sort of spool arrangement to keep the heater coils tight and flat. The leads were then fed through the grommets and the whole boiler assembly tightened up with the bottom nut.

More to come.
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Very, very nice George!
Can’t wait to see how well this will work out.

Most of the stuff seems to be stainless steel and such. Is the tin can part of the heater a possible problem? They (tin cans) tend to have coatings inside (plastics or flash metals) and soft welds at the seams that could be an issue even if it is not in the vacuum part of the pump? I assume your temp will be low so that is not such an issue.

Still, the eye candy value alone has me glued to the photos.

Looking at the inventiveness, particularly using common utensils, is in the best traditions of Rutherford's work and "Building scientific apparatus" first edition....

Modern art with "found objects"! Nice work, George.

I can't wait to see the results of your trials. What will be your pumping fluid? Extra-virgin olive oil?

-Carl

Thanks for all the encouragement, guys! If I get some time today I'll finish up the foreline and braze it into the pump body. The final effort will be to shape and install the cowling and cooling fan(s).

As far as the can used for the boiler heat shield goes, there is no seam, but there is a very thin coating on the inside surface. I'll carbonize the coating with the torch and then clean up the can with some Scotch-Brite and Lysol PTBC. I'll also probably add a thermocouple to the bottom of the boiler. This will allow me to run some temperature/ pressure curves in the future.

I do remember something about distilling olive oil and using it in a desperate act as a diffusion pump fluid. I think it was in The Amateur Scientist column back in about 1960 or so. Anyway, I'll stick to DC 704 for this project.

Looks like it ought to work. You have poured the work into it. If this works out it will offer a cheap way for the DIYs to make a small air cooled pump more suited to a small fusor rather than have to pay the premium often seen on these small manufactured units.

Richard Hull

Very nice workmanship! I can't wait to hear how well it works, I would like to emulate this as it looks like a great project.

The pump body is basically finished at this point. Next is the cooling system. I've been thinking about different configurations and they all seem to have their own merits. I'll put a few thermocouples at the points where I'm interested in seeing the effects of the different methods.

I've added another pic of the boiler so that it's clear how the rope heater is installed and kept under control. It's important that the heater remain in intimate contact with the bottom of the boiler.

After torching the can to red heat to remove the plastic film on the inside and then Scotch-Brite scrubbing it clean, I decided to retorch it to get that 'gun metal blue' look. This is my concession to steampunking and Carl's comment about "art".
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Would one or two computer CPU fans with a metal shroud following the curve of the main body be adequate? If not a ThermalTake liquid CPU cooler might do, with a small copper tube spiral on the outside.. It comes with its own pump, radiator liquid-to-air heat exchanger and all the trimmings. I used them for cooled pmts, peltier cooled ccd detectors and ccd camera. The old models are available on ebay for cheap and can displace lots of heat in a small turn-key package.

George - beautiful!

You combine, art, science, practical engineering and a great sense of humor. Impressive work.

(Lots of real talent amongst those on this board.)

Dave Cooper

Traditionally, All air cooled pumps have a series of 6 to 10, 1/8" or thicker pure copper rings of at least 1" width brazed to the stack's exterior and a special shroud that funnels air from a very high CFM blower through the plenum. The air cooled pumps operation and ultimate depth of vacuum demands that the oil vapor be condensed before it can back stream.

Stainless steel is not a very good conductor of heat,but with a thin wall and good copper fins brazed to on, it should do fine.

There is a reason you don't see diff pumps with over a 3" throat that are air cooled. Naturally, Santovac or Pentovac fluids would help, but they are about $100.00 for 50cc.

Certainly, any suitably small DIY diff pump should be air cooled.

Richard Hull

Rich N - Thanks for the tip on the Thermaltake stuff. I was thinking about building some heat pipe devices to play with and then found a large selection of them on eBay. I bought a couple of new 125 watt units for $8 each. Plug and play. I couldn't even start the project for that price.

I'm also looking at Peltier coolers as a possibility. They're real cheap on eBay. Lots of methods to choose from.

After considering all of the alternatives for cooling the pump, the best strategy seems to be the method that I used on the glass pumps. This would be a hybrid water/air arrangement as pointed out by Rich N. It could obviously be done with air alone, but the amount of work needed to make good fins and fit and braze them to a tapered body would defeat the propose of making a simple pump. The other downsides to just air are excessive noise for above bench-top level work and the heat transfer in close proximity to the experiment area. Also, it's a lot of wind where you generally don't want it.

Being the cheapskate that I am, I'll use a Harbor Fright fountain pump and a container of water. The water will circulate through the 1/4" copper tubing that will be brazed onto the pump body and then through a simple mini radiator and back to the reservoir. This will allow placing the water and fan at any reasonable distance from the work/experiment area.

The pump is now basically finished and the next thread will cover how to setup and test the performance of this Bad Boy!

If the jet stack is mostly made of one pipe cut into sections, what's going to keep the forepump from sucking all the vapor out of the lower jet before it can successfully reach the top jet?

Chase

Hi Chase,

I believe to answer your question you need to understand the kinetic theory of gases, laws of flow of gases (particularly through small capillaries), and the accommodation coefficient of the oil vapor. I've been reading Vacuum Techniques by Saul Dushman and he has a very detailed discussion of the theory and operation of many vacuum pumping techniques (including diffusion pumps).

One of the key fundamental concepts that allows a diffusion pump to work is the fact that the oil vapor condenses when it hits a metal surface, and as long as the temperature of the metal surface is low the oil will not re-evaporate. Once condensed, with the help of gravity, the oil will return to the boiler. So long as the oil vapor touches a cold surface (cooled pump wall, foreline wall, foreline baffle) no oil vapor will leave through the roughing pump. Of course this same concept is what makes a diffusion pump failure cause such a mess. If the roughing pump fails or the vacuum vessel is opened to atmosphere then the oil vapor molecules coming out of the jets collide with many molecules causing them to lose their momentum towards the wall. Once their momentum towards the wall is lost the direction becomes random. Due to the small mean free path because of the failure (or maybe more correctly because of the higher pressure), the oil vapor molecules make there way out everywhere until they eventually come in contact with a wall causing an oily disaster.

I'm a newbie here, haven't fired up my pumping station yet, but this is my current understanding from my reading.

Bruce

George -

I also use an inexpensive fountain pump in a 5 gal plastic bucket for the diff. pump cooling system. Also had available an old chevy heater core, that leaked under radiator pressure, which along with a spare muffin fan, made a very effective closed cycle system - that doesn't leak (!).... water amount is about 1-2 gal, usually.

There are some nice commercial units that surface from time to time on ebay, that have a pump-fan combination with a SS water tank and lil copper radiator.

My unit needs a water top off of about 1/2 gal or less, about once a week in hot weather, and once a month in the winter months.

Big factor I have to control, is the dog drinking out the bucket.... With miscellaneous, bugs, copper residue and lime from the water, I was concerned about his safety. But he's alive and thriving, so it must be ok for him.

Dave Cooper