The system will be based on the polish Unitra-Unima components. No often to come by outside my country, but for other hand they are quite typical. Almost all the parts I’m using come out of dumpsters at my work (yes, I’ve access to very interesting scientific dumpsters ).
The system may look quite complex at first look, and it’s possible to get vacuum without more than half of the hardware I’m using. For other hand this layout is based on the technological setup used in commercial appliances like sputtering systems etc. so it is almost the most flexible and comfortable diffusion pump based system layout.
The main highlights are:
- It’s possible to vent and pump the chamber many times without need to shut down restart the diffusion pump.
- The oil back-streaming is minimal.
- There is no complicated shutdown procedure - just switch off and go home.
The diagram of the system: 1. Two stage rotary vane pump. 2. Foreline vacuum canister. 3. Oil diffusion pump. 4. Cooled baffle. 5. Diffusion pump isolation gate valve. 6. Chamber pump valve. 7. Diffusion pump forevacumm valve. 8. Chamber vent valve. 9. Foreline isolation valve and rotary pump vent combination valve. 10. Oil trap. 11. DN100 chamber flange. 12. Cooling water circulation pump. 13. Water reservoir. 14. Foreline pirani gauge. 15. Chamber pirani gauge. 16. Bayard–Alpert high vacuum gauge.
The whole system will be mounted on the wooden trolley and any desired chamber can be connected to the CF100 flange at the top (11).
The gate valve (5) allows to isolate the diffusion pump at any time. So it’s possible to vent the chamber at wish with the valve (8) and keep the diff pump running. When the chamber needs to be pumped again the forevacuum valve (7) is closed and chamber pump valve (8) opened to pre-evacuate the chamber. The vacuum canister (2) keeps the back pressure for safe operation of the diffusion pump. As the chamber pressure reaches the desired level the valve (6) is closed and valve (7) opened again. Then the gate valve (5) may be safely opened to pump the chamber to the high vacuum by the diff pump. As the chamber is pre-evacuated by the rotary pump there is no oil vapor burst from the diff pump.
The vacuum canister also simplifies the shutdown procedure - it’s enough to just close all the valves and turn off the heater. The backing vacuum will be held by the canister during the cool down of the boiler. It’s however desired to keep the water circulation to shorten the cool down time.
The combination valve (9) allows to isolate the foreline from the rotary pump (1) and vent the pump itself, to prevent oil flow into the vacuum port.