Scroll pump technology is also a dry technology, and can reach to 0.1 Torr, and in some cases as low as 0.001 Torr. Rotary vane vacuum pump technology and hybrid pumps (which combine rotary vane and diaphragm technology for fine vacuum with low maintenance) will reach as low as 0.001 Torr, while turbomolecular pumps can reach as low as 10-11 Torr, provided they are assisted by a “roughing pump.”
The roughing pump (often diaphragm or rotary vane) brings the pressures from atmospheric conditions to the range of 1 Torr or 0.1 Torr; the turbomolecular pump picks up from there to create the deeper vacuum.
Oil-free and particle free diaphragm pumps are usually preferred for those who need a roughing (sometimes called fore pump or backing pump) for small and middle sized turbomolecular pumps, because some diaphragm pumps can provide service intervals that match the very long service intervals of turbomolecular pumps.
An important principle is that the deepest vacuum is not the best vacuum for any application. The best scientific performance will be achieved by using a pump that produces vacuum in the most appropriate range for the application.
The level of vacuum needed for each of the applications noted earlier differs across a wide range. Many lab applications are accomplished in the “rough vacuum” range, down to about 1 Torr or 29.98 in. Hg. (gauge). Processes that operate in this range include filtration, aspiration, rotary evaporation, centrifugal concentration, gel drying, vacuum oven drying, and solid-phase extraction.
Such applications are best served with diaphragm pumps; the vacuum is in the right range and the operations are clean (no oil is needed), low maintenance, and can be made very chemical resistant, if needed.
Vacuum in the range between the lower limits of “rough vacuum” and 0.001 Torr is called “fine vacuum.” Laboratory processes requiring a fine vacuum include freeze drying, Schlenk lines, and residual drying. As noted earlier, this vacuum can be reached by rotary vane, hybrid and some scroll pumps. The correct choice will depend on the sensitivities of the application to oil, for example, or to dust that may be generated by the dry seal in a scroll pump.
Vacuum pumps are often integrated into other instruments and equipment as OEM (original equipment manufacturer) components. Such applications include gas sampling (e.g., for environmental testing or process monitoring), laser etching equipment in semiconductor manufacture, and test chamber evacuation in analytical instruments to ensure accurate results. They are used to evacuate test chambers and eliminate the influence of environmental conditions.
It is essential to consider your application requirements in order to choose the vacuum technology that is best suited to your laboratory and process needs. Start by defining the process for which vacuum will be used. Then define the level of vacuum and pumping speed needed. Finally consider chemical resistance, control requirements, maintenance intervals and environmental concerns (e.g., energy use, waste vapor capture) to determine the right pump.
These considerations will help narrow down which pumps will accommodate your applications and achieve the lowest lifetime cost of ownership. Then talk with your preferred vendor to avoid a mistake that can compromise your samples or process, or leave you with too much or too little capacity from your pump.