Rotary Vane Vacuum Pump Question

[mhrob24]

TL;DR Summary

What is causing the gas in the refrigerator to initially rush inside of the one chamber (I know that chamber is at a lower pressure than that of the refrigerator…..but how?)r

So in the image below from a video I watched , the narrator states “gas pressure from the refrigerator rushes into the low-pressure chamber “

So, I do understand that gas will push its way into a low-pressure area from a high-pressure (high to low)….but what I am unclear of is to how that chamber is at a lower pressure than the pressure in the refrigerator.

From what I see, the rotor spins, traps a volume of air, and that volume begins to decrease as the rotor continues its turn. Thus, pressure and temperature increase (in one of the chambers) and the gas is expelled out into the atmosphere through the outlet port. So what is causing the gas inside the refrigerator to rush into the chambers? Like, why is the one chamber at a lower pressure than that of the gas pressure inside the refrigerator?

From what I know, a lower pressure area is created when you remove gas from a trapped area (like a suction cup….it pushes the air out from inside of it and the atmospheric pressure is what’s holding it up. There is lower pressure inside of the suction cup, so the atmospheric air is trying to force its way in ). So is the gas that’s being expelled into the atmosphere causing the chambers created by the two vanes to be at a lower pressure than that of the pressure inside the refrigerator? I don’t think that can be, because it’s only when that chamber reaches a certain pressure that the valve is opened and air is released…..idk, I know I’m fundamentally screwing something up but I don’t know what. I understand how other vacuum’s work, but this is tripping me up a bit.

 

[Drakkith]

So what is causing the gas inside the refrigerator to rush into the chambers? Like, why is the one chamber at a lower pressure than that of the gas pressure inside the refrigerator?

The moving vane (red piece labeled with #3 in the below picture) creates a vacuum as it moves by the inlet, and the pressure difference is what pushes the gas into the chamber. Notice how as the vane passes by the inlet (blue arrow) it creates a chamber that increases in volume as the vane rotates. The new, expanding chamber is essentially empty space (or would be if gas didn't rush in) since the vanes seal against the walls of the pump. The gas molecules from the inlet are pushed out into this empty space by the gas molecules 'behind' or 'upstream' of them until the other vane comes along and cuts the inlet off from this chamber.

Or, in other words, the pump creates a region of low pressure that is filled by gas from the higher pressure inlet.

 

[Baluncore]

….but what I am unclear of is to how that chamber is at a lower pressure than the pressure in the refrigerator.

The pressure starts out the same. As the inlet port is exposed, the pump chamber has a minimum volume which quickly matches the pressure at the input port. The volume of the pump chamber is then increased, so the pressure falls as the total volume of the connected input and pump increases. Gas is shared between the port and pump volumes, so gas is drawn from the inlet port into the pump chamber as the volume increases and pressure falls.

 

[mhrob24]

The pressure starts out the same. As the inlet port is exposed, the pump chamber has a minimum volume which quickly matches the pressure at the input port. The volume of the pump chamber is then increased, so the pressure falls as the total volume of the connected input and pump increases. Gas is shared between the port and pump volumes, so gas is drawn from the inlet port into the pump chamber as the volume increases and pressure falls.

OK, I think I know what you’re saying. So just to confirm I am understanding correctly, you’re saying that as that vane passes the inlet and continues on, the volume in the chamber that's exposed to the inlet is increasing. So the pressure is decreasing in that chamber, which means that the gas in the refrigerator is draw into that chamber because it’s now at a lower pressure than the gas in the refrigerator (it WAS equal, but as the volume increased, differential pressure occurred)?

Sorry for continuing questions, but I am interning right now, and I’m working on a vacuum pump for a brake booster, so I want to be 100% sure I am explaining and comprehending this correctly. Thanks for your time (the both of you!)

 

[Drakkith]

So the pressure is decreasing in that chamber, which means that the gas in the refrigerator is draw into that chamber because it’s now at a lower pressure than the gas in the refrigerator (it WAS equal, but as the volume increased, differential pressure occurred)?

Yes, that's right.

 

[mhrob24]

Yes, that's right.

Thank you both!