Pressure = force/area
20 ml syringe has larger area
Can pull a larger vacuum and a larger volume
The 20 mL syringe has both:
- A deeper stored vacuum (more negative starting pressure), and
- A larger reservoir volume to draw blood into before pressures equilibrate.
Boyle’s law P1V1=P2V2
If v1 is 10 ml and v2 is 20 ml then P2 will be lower than P1