A Short Course in Lab Vacuum, Part 1: Vacuum Capacity

How deep a vacuum do I need?
When determining if a pump can meet the needs of your application, it is best to first compare the application’s required vacuum level to the pump’s ultimate vacuum. Ultimate vacuum is the deepest level of vacuum a pump can achieve. For example, a vacuum pump with an ultimate vacuum of 80mbar is capable of vacuum levels between atmospheric pressure and 80mbar. Most common lab applications operate in the “rough” vacuum range, i.e., between atmospheric pressure and 1mbar (0.7torr). As such, most labs can take advantage of the low maintenance, oil-free performance of a chemistry-design diaphragm pump.

Vacuum filtration, liquid aspiration, and similar applications that use vacuum to move liquids are best served by a vacuum depth of 80mbar. A vacuum level deeper than that will not offer significantly better performance, and will often have undesired side effects, such as evaporation of the filtrate. For these operations, select our ME series pumps.  If the fluid to be moved involves liquids other than water, or contains corrosives, such as bleach, a Chemistry-design pump should be used.  For simple filtration of saline solutions, or biological media, an aluminum-FKM (“non-‘C’”) pump may be used.  It is a good idea to use a filter before the pump to keep aerosols from entering.

In evaporative applications, the ultimate vacuum generated by the pump must meet or exceed the solvent’s vapor pressure. For instance, evaporation of dimethyl formamide (vapor pressure: 2.7mbar) requires a pump that can achieve a vacuum depth of 2.7mbar, such as the VACUUBRAND® MD series (2mbar) pumps. Remember, for longest pump life, a Chemistry-design diaphragm pump with PTFE flowpath should be used for evaporation, whenever possible

Freeze drying (lyophilization), molecular distillation, and other applications that utilize vacuum depths below 1mbar require the use of roots pump or rotary vane technology. For these applications, we recommend the VACUUBRAND® RC6 Chemistry-HYBRID pump.

BrandTech is always willing to help in selecting an appropriate vacuum pump for your needs. Please give us a call!

What about flowrate?
A pump’s flow rate is the volume of gas or vapor it can move per unit of time. The flow rate required for a particular application is determined by a number of factors, including the application’s vapor volume, whether a condenser or cold trap is used (reducing vapor load), time requirements, and system leakage. If a pump can’t generate enough flow at the desired vacuum level, the application will proceed much more slowly, or in extreme cases, not at all. The stated flow rate figure for most vacuum pumps reflects the pump’s capacity at or near atmospheric pressure, not under vacuum. Pumps with the same ultimate vacuum can differ in their flow rate under vacuum, so be certain to inquire about a pumps flow curve to determine the flow rate at your application’s vacuum depth.