Hi, recently bought EC.4 and I have few questions whether it's normal and expected from this pump. Sorry for possibly stupid questions My old vacuum pump is oil-less so I'm kinda new to this pump.

Pump was filled with oil which came with vacuum pump up to half of the sight-glass.

1. When pulling vacuum oil vapor separator looks like this. It settles down as soon as full vacuum is reached. Is it supposed to work like that? Catch oil and collect it in the container?

2. When full vacuum is reached oil has lots of air bubbles. They disperse when pump is off. Is it normal?

3. What is the purpose of return check valve? I thought it was supposed to hold vacuum when pump is off. But as soon as I switch pump off - vacuum gauge drops to zero and you can hear air being sucked back to the vacuum pump through oil mist separator. So is the valve for holding vacuum or just for keeping oil getting sucked back into the tubing?

Thanks

Thanks guys.
My bags are small, not larger than 50x50cm.
1. I've been advised by local vacuum equipment supplier (they also sell DVP products) to fill oil just a bit below half of the sight-glass. Did that. Now there's much much less oil going through oil separator.
3. I've disassembled the inlet port to check non return valve. Don't care about warranty. I know I lost it. The diaphragm was not seated properly and could not move at all. Basically one prong was in the hole, other two were resting on the edge. Photo shows properly seated diaphragm.
Looking at it it seems logical there should be compression spring sitting below diaphragm. So the question is should there be spring or not? Or should I just get some inline non return valve and be done with it

Thanks again guys!