Automatic air release valves.

But nothing works if the pressure in the pie is less than atmospheric pressure.

It sounds to me like you are creating a vacuum / low pressure in your inlet pipes? Fix the leaks or run slower or increase the liquid height in the tank.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

If I pump the oil from a drum or another IBC, air introduced into the system...

Best Regards
Roman Katz

You're not giving us any information here to help you.

What is the "oil"
What size is the suction line?
What flow rate is the pump?
IS the air getting in by a vortex in the drum / IBC?
Are you pulling a vacuum in the inlet?
Where do you think the air is getting in (remember we can't see your system or how you work)
what height is the pump above or below the liquid level?
Any photos / sketches?

My suspicion remains that you're trying to pump too fast and the gear pump is either pulling a vacuum in the oil as it is too viscous to flow into the pump or air is entering the inlet piping somewhere

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Oil is a lubricating material, 60-360 CST at 40degC. The system is simple, gear pump(100LPM) is connected to 2'' cs piping. at one side flexible plastic tube that can be attached to IBC or placed inside the drum. On the other side, the outlet/discharge, again another flexible tube.

The inlet flexible tube intakes air once the drum/IBC are emptied till the pump is stopped and the air remains there till it is forced out by the liquid in the next operation.
So the cycle is at first the pump makes a lot of noise, then it runs ok and at the end it makes noise again.

Best Regards
Roman Katz

...Are you really asking if there is a way to avoid drawing in air to the suction line from an empty vessel? That's what always happens if you completely empty a vessel using a pump...

Either get used to the noise and (slightly) increased wear on the pump, switch to a different style pump, or don't fully empty the container.

Well is the pump below the liquid level for the new tank?

Why not fit a vent valve on the pump inlet and open it up until some of the oil comes out or fit an auto bleed valve and then BEFORE turning the pump on isolate the auto bleed to stop it allowing air into the inlet line.

If the pump is higher than the liquid level then you'll need some sort of suction or vacuum. Either a small hand pump or a vacuum line and do the same thing.

You could even use something like an industrial vacuum cleaner onto the end of an auto shut off valve to stop oil coming through.

MAny ways you can fill the inlet line on a new pump out.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Have you tried the 99.98% Barrel Emptying Pump:

Link

Hi,
Sorry you don't use the right technology !

https://www.flux-pumps.com/en-DE/products/drum-and...
https://www.pcm.eu/en/industry/pcm-solutions/peris...

Pierre

Thank you all

Best Regards
Roman Katz

So what are you going to do?

Change anything?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

I think that I will eliminate air suction by tilting the drums or by using IBC.

It will be much cleaner at least.

Best Regards
Roman Katz