Most laboratories will have a vacuum pump. They are widely used across labs of all disciplines for a range of tasks from basic filtrations or evacuating a desiccator right up to use with large equipment such as vacuum ovens or rotary evaporators.
The two most common types are rotary vane or diaphragm pumps – but what do these mean and what is the difference?
Rotary Vane Pumps
Rotary Vane pumps use moving vanes to move volumes of gas through the system and out of the outflow. The stages of operation are shown in the diagram below;
This mode of operation means that they require oil in the system, to lubricate the moving parts and to create a seal so the gases are isolated. As such Rotary Vane pumps do require more regular maintenance such as changing the oil. Many models feature a sight glass to easily view the oil and gauge when it needs changing.
Rotary Vane pumps are able to achieve much lower vacuums than diaphragm pumps, so are often used in more demanding applications such as with glove boxes or freeze dryers.
Diaphragm pumps are usually oil free and low maintenance. They work by moving a flexible diaphragm which forces air in through one side and out the other by control valves, as shown below;
This operation does not require oil so there is less maintenance requirement. The diaphragm may need replacing annually or even less often depending on usage.
Diaphragm pumps do not achieve as low vacuums as Rotary Vane pumps but are a popular choice for everyday use with filtrations, desiccators and for aspiration of waste liquid in microbiology. Larger diaphragm pumps are also available to use with rotary evaporators or vacuum ovens.
Care should be taken when choosing a Diaphragm Pump on the diaphragm material – those with PTFE seals have better chemical resistance and can be used even when acidic or solvent vapours are present – they are often called “chemical duty” pumps. Some more basic models are only suitable for working with aqueous (water based) vapours, these are commonly used for basic filtration work.
See our full range of vacuum pumps here and try out the application tags to narrow down the selection.