#2 FAQ - Mechanical Pump - Diffusion pump?

[ggombert]

I use a Lesker foreline (metal wool) trap to keep mechanical pump oil out of the Edwards diff pump.

http://www.lesker.com/newweb/traps/fore ... pgid=replc

Glenn

[John Futter]

Glenn

Richard I hope was not referring to Alexis post
The air cooled pump will still work without the forced air cooling albeit with vastly reduced pumping speed, and by not cooling it, it allows the diff pump oil to rise up into your vacuum system --very difficult to clean off.

[ggombert]

John,
If you look carefully at the back of the picture that I posted you will see a 2.75 in fan on the back of the diffusion pump.
Glenn

[daghike]

Thanks Alex,

I have gotten down to 2*10-6 since I added 100ml more of oil.. There is definitely a small leak inside that is hindering the pump down. its not a big one thats why its hard to find it.

for ex. when roughing the chamber the pressure was lower than when just backing the diff pump. somehow when the diff pump oil got in motion it overrides this leak somewhat and does the pumping out.. just hitting this ceiling.

will do one more round of leak testing and replace it with another diff pump.

cheers,
Don

[Richard Hester]

Noted - folks that have an air-cooled pump with no fan - fix that...

[Tom McCarthy]

A quick question, if you use a fore-line trap with the required two bellows valves and a diffusion pump would you still need the connector between the mechanical pump and diffusion pump?
Also, if you are using a gate or third bellows valve to connect the diffusion pump to vacuum chamber and regulate the vacuum's "flow" would you still need the second connector?

Tom

[Richard Hull]

You will always need to connect the mechanical pump directly to the diffusion pump. Between them you can have a trap and, or, a valve, but you must connect them together.

Richard Hull

[Tom McCarthy]

So the trap accompanied by its two bellows valves will act as the connector and the bellows valve or gate you use to connect the diffusion pump to the vacuum chamber is the other connection.

Tom

[Chris Bradley]

... connect the mechanical pump directly to the diffusion pump.. Between them..a valve

hmm... I'm thinking that is tempting fate that someone would close the valve with the diff pump still 'on'. Messy?

[Richard Hull]

Sorry about that. If you use an oil trap in the foreline, it needs one valve. A cold trap in the high vacuum line will need none. I have supplied an "in order" hookup with options.

Must haves items are in all caps. Optional items not needed for fusion are between asterisked lines.

MECHANICAL PUMP
UP TO AIR BLEEDER VALVE (can be a ball valve) OR KF DISCONNECT (AVOIDS SUCK BACK)
SHORT HOSE
BELLOWS VALVE

*******************************
oil trap/micro maze, etc.
bellows valve
******************************

DIFFUSION PUMP

*****************************
cold trap
****************************

BELLOWS OR GATE VALVE
FUSOR CHAMBER

There you have it.

Richard Hull