Experimenting with a vacuum pump

[DDesulgon]

Hello,
I would like to carry out a few experiments with a vacuum pump under a vacuum bell jar. However, I have no experience with this and the operating instructions could only help me to a limited extent.
Specifically, I am interested in the sequence for switching off the pump: When I have pumped the air out of the bell jar, can I then simply switch off the pump? Or will the vacuum in the bell jar damage the pump or suck the oil out of it or something similar?
What are the next steps when dismantling the experiment? Let air back into the bell, pull off the pump hose... In what order should one proceed?

 

[berkeman]

Can you post links to the pump and bell jar info? Most likely it's fine to switch off the pump and just watch the vacuum gauge to be sure you don't have a leak, and then just crack the bleed valve when you are ready to return it back to atmospheric pressure, but it would be good to see the pump and bell jar info to be sure.

https://www.spectrum-scientifics.com/High-Vacuum-Pump-Deluxe-Experiment-Kit-p/1907.htm

 

[DaveE]

It is common for there to be a valve at the pump to reduce the leakage back through the pump (which should be small). It may not be necessary if you don't need a hard vacuum or you don't need to maintain it for a really long time. You'll also need another valve to let air back into the chamber at some point.

 

[DDesulgon]

Thanks for the answers and the link! Unfortunately I cannot find the information about the pump and the bell jar online.
Do I understand it correctly that the following way is safe?
- Pump off air
- Close the valve between the pump and the bell jar
- Switch off pump
- Remove the hose from valve
- open valve to let air back into the chamber (I have only the one valve)
Or could something still potentially go wrong with this procedure? And if so, what would be an alternative approach?

 

[bob012345]

Hello,
I would like to carry out a few experiments with a vacuum pump under a vacuum bell jar. However, I have no experience with this and the operating instructions could only help me to a limited extent.
Specifically, I am interested in the sequence for switching off the pump: When I have pumped the air out of the bell jar, can I then simply switch off the pump? Or will the vacuum in the bell jar damage the pump or suck the oil out of it or something similar?
What are the next steps when dismantling the experiment? Let air back into the bell, pull off the pump hose... In what order should one proceed?

What kind of experiments are you wanting to do if I may ask?

 

[erobz]

Thanks for the answers and the link! Unfortunately I cannot find the information about the pump and the bell jar online.
Do I understand it correctly that the following way is safe?
- Pump off air
- Close the valve between the pump and the bell jar
- Switch off pump
- Remove the hose from valve
- open valve to let air back into the chamber (I have only the one valve)
Or could something still potentially go wrong with this procedure? And if so, what would be an alternative approach?

I would do something like this:

The ball valve should be vacuum rated, and I believe a "T port".

 

[tech99]

I have used a school vacuum pump with good success for the bell jar experiment and also for gas discharge tube demonstrations and a miniature cathode ray tube. From memory we had a little valve to seal the bell jar once it was pumped down. Here is a link to a school bell jar: https://www.philipharris.co.uk/product/physics/bell-in-a-bell-jar-experiment/b8l11149. You need to let the air in again slowly.

 

[DaveE]

Thanks for the answers and the link! Unfortunately I cannot find the information about the pump and the bell jar online.
Do I understand it correctly that the following way is safe?
- Pump off air
- Close the valve between the pump and the bell jar
- Switch off pump
- Remove the hose from valve
- open valve to let air back into the chamber (I have only the one valve)
Or could something still potentially go wrong with this procedure? And if so, what would be an alternative approach?

Sounds good to me. The only thing I'd worry about is the bell jar strength; but it will be fine if it's intended for vacuum use.

 

[bob012345]

Sounds good to me. The only thing I'd worry about is the bell jar strength; but it will be fine if it's intended for vacuum use.

Just wear safety glasses.

 

[tech99]

I have used a safe plastic bell jar made by Nalgene, but expensive.

 

[DDesulgon]

I did it as described above and it worked nicely. Thank you all for the quick and excellent help, as always.