Vacuum Solutions for Scientists Pump Sizing for Filtration
Flow Requirements for Effective Filtration
The pump must meet two primary flow needs:
- Evacuation of Air: As the air is removed from the apparatus, pressure drops, creating the differential required for filtration.
- Overcoming Leakage: Any vacuum system is susceptible to leaks, which can prevent achieving the deepest vacuum possible.
Common leakage points in lab filtration include:
- Loose connections between tubing and the filtration flask.
- Gaps at the gasket of a Buchner funnel on a side-arm flask.
Special Consideration for Manifold Filtration: In multi-sample setups, individual filtrations complete at different times, creating potential leaks (or “break-throughs”) where air enters through an open filter, reducing the pressure differential for remaining samples. Installing stopcocks or valves at each manifold position helps prevent this. A pump with higher rated pumping speed can further compensate for leakage by restoring the vacuum quickly after isolating “break-through” points.
Using Pump Curves to Evaluate System Performance
Each pump produces a specific flow rate at a given vacuum level. By observing the vacuum level and using the pump’s curve, one can estimate the flow rate and identify the extent of any leakage in the system.
Troubleshooting Common Filtration Issues
If issues arise during filtration, consider the following diagnostic steps.
- If the pump achieves near its ultimate vacuum when connected:
- Check for blockages in the filter or funnel.
- Consider a pump with a deeper ultimate vacuum for increased pressure differential (100 mbar is generally sufficient). Ensure that the vacuum level is not deeper than the filtrate’s vapor pressure to avoid evaporation.
- If the pump does not reach its ultimate vacuum when connected:
- Inspect for leaks in the apparatus and address them.
- Ensure there is no sample “break-through” causing the leak.
- If necessary, use a pump with a higher pumping speed for increased flow capacity.
In Conclusion, by carefully sizing and selecting a pump, you can achieve optimal filtration efficiency, even with challenging sample conditions or complex setups.
