Vacuum systems for clean and reliable analytical environments
Vacuum pumps play a crucial role in many types of analytical instruments by creating the correct vacuum conditions which are necessary for accurate, precise, and reliable measurements. Vacuum pumps remove air and other gases from instrument chambers and in the preparation of samples, by the creation of a vacuum environment which reduces potential interference from residual atmospheric gases. This allows for detection of signals from the smallest of samples, which is crucial to the performance of the wide range of analytical applications.
There are several types of vacuum pumps, ranging from rotary vane (RV and E2M), scroll and multistage roots primary pumps (nXRi and nXLi) to turbomolecular and ion getter secondary pumps which are employed in analytical instruments.
Primary pumps exhaust to atmospheric pressure and achieve pressures in the Low and Medium Vacuum levels; they can use oil or be ‘dry’.
Secondary pumps, which achieve High and Ultra-high vacuum levels, require a supporting primary pump. The type of vacuum pump used depends on the specific requirements of the analytical application.
All our vacuum pumps and their controllers are developed with leading OEMs in the analytical instrument field in mind. In some cases, when an off-the-shelf pump doesn’t match the space available or performance requirements of your process, then our “Bespoke Product Development” (BPD) team will develop a customised vacuum solution. This is co-engineered with you, specifically for your application.
Vacuum systems for mass spectrometry
Mass spectrometry (MS) is a scientific technique used to measure the mass and relative amounts of atoms and molecules in a sample. In essence, it can be considered as a chemical analyser. Firstly, the sample needs to be “ionised”, which can be done by various techniques depending upon the sample type. The ions are then separated, again by employing the most appropriate method, according to their mass-to-charge ratio. They are then detected, and the signals finally processed to give the resulting mass spectrum.
Mass spectrometry has a wide range of applications, including the fields of chemistry, biology, environmental science, pharmacology, and medicine. It can be used to identify unknown compounds, to quantify the amounts of specific compounds in a sample, and to help determine the structure of complex molecules.
The accuracy and precision of mass spectrometry measurements rely upon varying vacuum levels. Vacuum pumps remove residual gas molecules which might interfere with the measurement process and thus ensure that the mass spectrometer operates within the desired vacuum conditions.
Common vacuum pump technologies for mass spectrometry include:
Rotary vane pumps (RV and E2M)
The mechanism of an Oil-Sealed Rotary Vane Pump (RVP) consists of a set of sliding blades held in a rotor which rotates eccentrically within a cylindrical stator housing. As the oil-lubricated blades rotate with the rotor, centrifugal force presses them onto the wall of the stator housing by centrifugal force. Gas entering the pump is confined by the blades and compressed into a reducing volume until it reaches the pump outlet whence it is exhausted to atmosphere. One or two stage RVPs are used and provide different ultimate pressures.
Multistage roots pumps (MSR) (nXRi and nXLi)
In its simplest form, a MSR is a dry roots pump employs two counter-rotating interconnected ‘lobed’ rotors which rotate within a matched profile stator housing. Gas enters the dry pump through an inlet flange located perpendicular to the rotors and is then “isolated” between the rapidly rotating rotors (which are spinning in opposite directions), compressed, and then fed to the next stage. The geometry of the rotors creates compression and hence each stage produces a progressively higher pressure. A MSR pump employs typically seven rotor stages on shared shafts, the exhaust stage of one set is connected to the inlet stage of the next and so on. The compressed gas is then expelled to the atmosphere via the final, exhaust stage.
A dry scroll pump consists of two co-wound spiral-shaped scroll geometries contained within a vacuum-housing. One scroll-form is fixed whilst the other orbiting scroll moves eccentrically without rotating, within the other. Gas enters the (outside) open end of the spirals and, as one of the spirals orbits, a quantity of gas is isolated between the scrolls and is “squeezed and transported” between the two spirals. As this isolated “slug” of gas moves towards the centre of the mechanism, the volume it occupied decreases and, as such, this isolated gas quantity is continuously compressed until, at the centre of the housing, it is expelled to atmosphere pressure via a non-return valve.
Turbomolecular pumps (TMP)
These pumps work by using very high rotational speed turbine blades (of the order of 1,000 Hz) to remove gas molecules out of the instrument vacuum chamber and into the inlet of the pump. They are used extensively because they can create a wide range of vacuum levels required, ranging from 10-2 to 10-10 mbar, for the various processes employed in an instrument.
OEMs frequently have specific requirements, in which case Edwards Bespoke Product Development (BPD) group co-engineers a vacuum solution that fits the customer’s exact needs.
Vacuum systems for electron microscopy
Scientists working with electron microscopes identify the tiniest scale of matter on earth, and require quiet, vibration-free and reliable vacuum pumps.
Electron microscopes (EM) employ a range of vacuum levels within them to achieve their desired performance. In the case of the electron gun at the ‘source’, an UHV environment is required to prevent damage to the electron source. This also enables the electron beam to travel from the source, through the electron column and on to the sample without being scattered or absorbed by residual gas molecules. The electron beam then interacts with the sample, creating signals that are detected and used to produce an image.
To achieve high-resolution images, the vacuum in the microscope chamber must be of high and consistent quality, including UHV conditions in some cases, thus requiring the use of vacuum pumps.
Various vacuum pump technologies are used in electron microscopy; most commonly these are rotary vane pumps, diaphragm pumps, scroll pumps, turbomolecular pumps and ion pumps. Depending upon where in the microscope the vacuum pump is employed, vibration from the pump must be minimised to prevent image disturbance. In certain EM configurations (Environmental Scanning EM) the pumps must be capable of continuously pumping an environment of water vapour at the ~10 mbar level.
Through the Gamma Vacuum range, we now offer ion, titanium sublimation and non-evaporable getter pumps to complement our mechanical pumps. This completes our range of products to deliver working pressures from atmospheric through to UHV allowing a truly complete vacuum solution offering.
Vacuum pumps used in electron microscopy:
Ion Getter pumps (IGP)
Need to be brought down to high vacuum levels before being switched on. This is usually achieved by using a turbomolecular pump in combination with a backing pump (diaphragm, scroll or rotary vane). Once the desired vacuum level (usually 10-6 mbar or less) has been achieved, the IGP can be switched on. IGP vacuum pumps are available in three basic types: the Conventional Diode (CV) pump; the Differential Ion (DI) or Noble Diode pump and the Triode pump. All three variants consist of a vacuum chamber, varying in size according to the pump’s speed, a Conflat flange and a high voltage feedthrough. Externally they have pair of ferrite magnet plates linked by a yoke which produces a magnetic field of the order of 0.12 T.
The CV pump is best suited to applications which require reactive gases (such as oxygen, hydrogen, hydrocarbons, nitrogen, and water vapour etc.) to be pumped. Internally it contains a pair of titanium cathode plates held at ground potential which “sandwich” a series of electrically isolated stainless steel anode tubes. A high voltage, typically of 7kV, is applied to the anode tubes causing free electrons to be emitted. These electrons travel in a spiral motion (caused by the magnetic field) and can eventually strike a gas molecule knocking off an electron creating a positively charged ion. This ion is then repelled by the positively charged anode tubes and drawn to the grounded cathode plate where it impacts the surface at high velocity where a chemical reaction takes place with the titanium cathode plate. Sputtering of titanium is also initiated which forms an active getter pumping layer of Titanium.
The DI getter pump has superior noble gas pumping capabilities but does lose some reactive gas pumping as a result. The titanium plates are replaced by tantalum ones. Gas molecules are again ionised by electron bombardment but when they accelerate and strike the tantalum anode plates, they are reflected as high energy neutrals which then go on to combine onto surfaces and are eventually getter-pumped by sputtered tantalum.
The Triode vacuum pump has a slightly different construction. Here, the tubes are grounded, and the cathode plates are replaced by anode titanium strips at a negative high voltage potential. Ions are generated in the usual way and are accelerated towards these strips where they impact and are released as high energy neutrals finally embedding themselves into the chamber walls and are getter-pumped by sputtered titanium. The titanium strips have sharp edges and as they are at high negative potential, they are prone to developing “whiskers” which can periodically “flash-over” causing some electrical instability over time.
IGPs, dependent upon the amount and types of gases present, can generate vacuums ranging from 10-6 down to 10-12 mbar. In Electron Microscopes, they are typically used on the electron column where their lack of moving mechanical parts mean they can produce vibration-free UHV conditions.
Vacuum systems for glove boxes
Glove boxes are the enclosed workspaces for handling materials in complete isolation, free from oxygen or moisture. To achieve this isolation, vacuum pumps evacuate ambient residual air from the glove box, which is then purged with an inert gas, such as nitrogen or argon, and sealed off. The low-pressure environment created by the vacuum pump prevents the external atmosphere from entering the glove box.
Several different types of vacuum pumps that can be used for glove boxes, including diaphragm pumps, rotary vane pumps, and scroll pumps. The choice of pump depends on the specific needs of the application, such as gas flow rates, vacuum level, and maintenance requirements.
Vacuum systems for X-Ray Diffraction (XRD)
XRD is a technique used to analyse the structure of materials by examining how they interact with X-rays. When X-rays are directed at a sample, they are diffracted in a specific pattern that can be analysed to determine the sample's crystal structure.
Vacuum is used in XRD to eliminate atmospheric molecules, which can scatter and absorb the X-rays, leading to reduced signal-to-noise ratios and less accurate data. By removing air molecules and creating a vacuum, the X-rays can interact with the sample without interference, resulting in better-quality data.
Vacuum is also used in XRD to reduce sample contamination. When the sample is exposed to air, it can become contaminated by dust, water vapour, and other airborne particles, which can interfere with the diffraction pattern. By using vacuum, the sample is protected from these contaminants, resulting in a more accurate analysis.
To create a vacuum in an XRD instrument, a vacuum pump is used to remove air molecules from the sample chamber. Different types of vacuum pumps, such as rotary vane pumps, diaphragm pumps, and turbomolecular pumps, can be used depending on the specific requirements of the instrument and the sample being analysed.