Rotary Vane Vacuum Pumps FAQ

* The temperature of the coolant

* Your pump - in particular the vacuum level at which it operates,

* The vapor pressure of your solvent at the temperature of your coolant.

For example, dry ice has a temperature of -78.5 Celsius. Acetone has a vapor pressure at that temperature of approximately 0.5 mbar. So, when operated with a two-stage rotary vane pump, with an ultimate vacuum of approximately 0.001 mbar, a dry ice trap would not be effective. A better choice would be liquid nitrogen, with a temperature of -196 Celsius.

Of course, a dual-stage rotary vane pump would be overkill to evaporate acetone. If a single-stage diaphragm pump, with an ultimate vacuum of 70 millibar was used to evaporate acetone, a dry ice trap would be considerably more effective.

To know whether your cold trap is being effective or not, the efficiency can be calculated by weighing your sample before and after drying to determine the mass of the evaporated solvent. This can be compared to the mass of the liquid collected in the cold trap. All of the solvent that is not collected in the cold trap can be assumed to enter the pump. In the case of a rotary vane pump, it can be assumed to be contaminating the oil.

VACUUBRAND® Chemistry diaphragm vacuum pumps, in the vast majority of cases, do not require cold traps to protect the pump from vapors, because the flowpath is made of highly resistant fluorinated plastics. In some high vapor flow applications, a cold trap can be desirable to reduce the vapor load on the pump, also known as "cryopumping."

• Warm up the pump before use.  By warming up the pump, and the oil inside of it, condensation is reduced.  A warm pump also performs it’s best.  A half hour of warm up time is optimal
• Use the gas ballast.  The gas ballast helps purge solvent vapors from the pump during use.
• Use an inlet cold trap.  An inlet cold trap can reduce the amount of solvent vapors entering the pump.
• Avoid particulates.  Particles entering the pump can score the walls of the pump, reducing it’s efficiency.  Additionally, the particles created by scoring of the pump can also cause damage, setting off a chain of events to catastrophic failure.
• Never block the pump outlet.  Back pressure on the pump reduces its efficiency, and can cause serious internal damage.  We do not recommend the mounting of any aftermarket accessories on a pump, except for original manufacturer equipment oil mist filters.
• After use, run the pump with the inlet blocked and the gas ballast open.  This helps purge any condensed vapors in the pump oil.  A half hour is usually sufficient.
• Check and maintain regularly.  This includes, but is not limited to monitoring of oil level and color, and regular changes.  Periodic measurement of pump performance can help prevent catastrophic failure.