Diaphragm Vacuum Pump Applications Generate low-maintenance vacuum
in the lab, pilot plant, and beyond! By Akbar Anwari, Marketing Manager, BrandTech Scientific, Inc.
Reprinted by permission of BrandTech Scientific, Inc. Diaphragm Vacuum Pumps Integrated Vacuum Systems
Vacuum Control Technology
Rotary Vane Diaphragm Pumps
| | Vacuubrand®
Chemistry-HYBRID Vacuum Pump | As newer and stronger environmental regulations are enacted, there has been a strong drive away from traditional oil-sealed rotary vane vacuum pumps. The following pumps allow users to remove oil from many applications and reduce oil usage in others, while substantially reducing maintenance. Diaphragm vacuum pumps are becoming increasingly popular for small to medium size applications as an alternative to oil sealed rotary vane pumps. Diaphragm pumps can be extremely low maintenance and quiet. Because the method of operation, the materials of construction can be selected for maximum corrosion resistance with only slight compromises in performance, and no compromises in diaphragm lifetime. It is best to choose a pump that generates superior flow rates at working vacuum levels, to provide fast pumpdown times and vapor transfer. Typical diaphragm lifetimes for these pumps range from 10,000 to 15,000 hours—that's years in many applications! Traditionally, diaphragm pumps, when employed in laboratory applications, were relegated to menial lab tasks such as filtration, due to their lack of performance and chemical compatibility. Modern multi-stage diaphragm pumps can provide vacuum levels throughout the entire rough vacuum range (atmosphere to below 1 mbar/torr) providing vacuum levels suitable for many tasks. Standard models can perform degassing of liquids, and even be used as backing pumps for wide range turbomolecular pumps. Chemistry-design models can perform nearly any evaporative task, except room temperature evaporation of very high boiling point solvents, such as DMSO or ethylene glycol. Pumps with high flow rates at working vacuum offer the advantage of being able to operate without a cold trap to enhance their performance. Diaphragm vacuum pumps are available in two different designs: - Standard Aluminum/FPM construction: Many non-evaporative applications can use a standard diaphragm vacuum pump constructed of aluminum and FPM (e.g., Viton®). Common applications for these pumps include vacuum filtration, vacuum impregnation, degassing, and backing of turbomolecular pumps.
- PTFE/FFKM construction: Applications that generate vapors incompatible with aluminum and FPM can often use a PTFE-designed pump. A fluoropolymer pathway is resistant to many common chemical vapors. Multistage models have an integrated gas ballast for high tolerance to condensates. Typical applications include rotary evaporators, centrifugal concentrators, gel dryers and vacuum ovens.
Because PTFE pumps are often used for evaporative applications, they are available as integrated systems, with solvent recovery. An inlet catchpot is included to capture performance-diminishing liquids that may condense in the vacuum line. In addition, since chemistry-design diaphragm pumps are resistant to many solvent vapors, cold traps are often not required in the vacuum line. Solvents can easily be captured at the pump outlet, at atmospheric pressure, with a cold water condenser. Electronic two-point control is also available for applications that are prone to "bumping," such as rotary evaporation. Applications that are particularly prone to bumping, such as rotary evaporation of volatile solvents, can benefit from a pump that utilizes special vacuum control technology. These pumps offer a speed-controlled motor and innovative controller software that allows the pump to find and follow boiling point curves automatically, dramatically reducing bumping. Because the vacuum level is continually optimized, evaporation can be up to 30% faster, and oversight is minimized, freeing up the operator to perform other tasks. If a bi-directional RS-232 port is featured on the unit, you can perform validation of vacuum procedures for GLP/GMP/ISO guidelines. The execution of complex pumping programs is also possible, and as an added benefit, the pump only runs as fast as necessary, reducing maintenance even further! Some applications, such as freeze drying, require fine vacuum, deeper than what is possible with a standard diaphragm pump. For these applications, rotary vane technology is indicated. One of the major drawbacks to rotary vane diaphragm pumps is that they are high-maintenance, requiring frequent oil changes. In a typical rotary vane pump, solvent vapors that enter the pump under vacuum condense when they hit the "brick wall" of atmospheric pressure at the outlet. This oil contamination reduces the oil's lubricating qualities, and can corrode the internal components of the pump. A company called Vacuubrand has devised a solution to substantially reduce this solvent condensation. A two-stage diaphragm section is connected as a backing pump for the rotary vane section. This reduces the rotary vane section's outlet pressure to approximately 2% of atmospheric pressure under normal operating conditions. This pressure reduction allows many of the vapors that would ordinarily condense in the pump oil to pass into the diaphragm pump, reducing oil changes by as much as 90% over conventional rotary vane pumps. | |