FAQ - Diffusion pump pictorial

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Richard Hull
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FAQ - Diffusion pump pictorial

Post by Richard Hull » Mon Sep 05, 2016 11:30 pm

What is in a diffusion, (diff), pump? To make an intelligent buy, you will need to know. I will supply a pictorial to go with the text.

Diff pump sellers vary from totally ignorant to decent ex-users who know their stuff. The latter seller is rather rare, the former is more common.

When buying a pump you need to either see images or ask intelligent questions of the seller.

1. Ask if it is complete (you will need to quiz further)
a. Is it a hollow tube or is there something inside the tube?
b. Does the heater in the boiler work? (ohmically good)
2. What kind of flanges does it have? ( diameter of inlet and outlet flanges, number of bolts, gaskets, etc.
3. Is it clean without tar or burned oil residues (cleaning of a burnt up oil mess can take days with solvent and elbow grease.)

The price you should be willing to pay will be a balance and trade-off against condition and size or pumping speed.

The typical 6 inch spherical fusor can get by easily with a 60 liter per second pumping speed. Larger fusors of odd shapes and not made of good vacuum stainless steel will need more pumping speed. 100-300 liters per second may be needed. Pumping speeds over 500 liters per second are a bit over kill for all but a giant fusor. Likewise, throat diameters over 4 inches will demand far more expensive adaptation to link to a small fusor and the oil load bill can be severe.

Pumps in the 60 liter per second range are often air cooled with a large attached fan. Larger pumps are almost universally water cooled and demand a source of constant flowing water either from a closed radiator based system or from a handy faucet and drain.

The images that follow are of a medium sized diffusion pump found in a typical professional system of the 50s thru the 1980's. Modern systems use the more expensive, mechanically and electronically complex turbo molecular pump. One advantage of a diffusion pump is that there are no moving or intricate parts to be damaged.

Note all of the components and connections...... Click on each image to enlarge.

Richard Hull
BigDiff (4).JPG
The two key components of the diff pump. It body and boiler and the critical jet stack. cleaned and removed ready for reassembly.
BigDiff (3).JPG
once cleaned and dried, the pump is ready to have the stack placed back in it.
BigDiff (2).JPG
With the jet stack removed, we look into the diff pump's hollow cylinder
BigDiff (1).JPG
The throat of a diff pump with the "spider" holding the "stack" in place
diff sale.JPG
Here is the restored pump ready for use or sale
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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