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FAQ - Diffusion pump pictorial

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