Piston suction pump versus external gear pump as vacuum pump

[johnthekid]

Hey guys, which one creates the higher vacuum (lower pressure vacuum)? A piston suction pump (that kind of looks like a syringe) or an external gear pump design (that used two external gears)? IMO I think it is the former but I want more explanations.

 

[Baluncore]

Welcome to PF.

The answer will depend on the required pressure and the volume that must be evacuated. The best pump will be the one with the least leakage.

I think my first choice would be an eccentric vane pump, with graphite vanes. Next would be a piston pump, and lastly, an external gear pump, which will have the highest leakage and need the most oil to seal the gear tips against the housing.

 

[johnthekid]

Welcome to PF.

The answer will depend on the required pressure and the volume that must be evacuated. The best pump will be the one with the least leakage.

I think my first choice would be an eccentric vane pump, with graphite vanes. Next would be a piston pump, and lastly, an external gear pump, which will have the highest leakage and need the most oil to seal the gear tips against the housing.

Thank you. As the piston pump is better suited for a vacuum pump design than the external gear pump design, I will pick the piston pump design that looks like a syringe or a piston bellows. What other reasons that make external gear pumps to be insufficient as vacuum pumps?