Brief outline of low vacuum pumps.
Low pressure vacuum pumps also known as backing pumps can be divided in to three sections
Rotary Vane – Oil seals
Dry Diaphragm pump
Dry Scroll pump
The Diaphragm pump is a dry, oil free pump which is commonly used where only a small vessel is evacuated, these are used in small laboratory apperatus.
The Rotary vane pump is more commonly used for larger vessels, the design is simple. But for the very increasing demand for “clean vacuum”, the oil used for the sealing makes this pump not ideal, as the oil tends to escape from the pump molecular form and works it’s way against the ‘flow’ entering the vacuum vessel causing contamination.
When pumping gasses that can contaminate the oil causing further problems, such as the oil viscosity change which can lead to pump failure.
Dry Scroll vacuum pumps have been designed to generate laminar atomic flow but hermetically sealing the pump from the driving mechanism.
Vacuum is achieved by using one fixed and one rotary orbiting inter-levered Archimedean spiral shaped chamber walls called ‘scrolls’. The gas enters the scroll arrangement and is forced, almost by peristaltic movement, to move towards the centre of the arrangements, with each movement the compress liquids or gases are further compressed until they reach the centre where they are released as exhaust gas.
The motor and gearing is sealed from the pumping scroll arrangement ensuring that these pumps remain oil free.
The applications in brief are:
Vacuum Extraction – NON-Chemical or corrosive applications