Selecting the Right Roughing Pump for High Vacuum Systems
Introduction
In the world of analytical instrumentation, achieving and maintaining high- and ultra-high vacuum levels is necessary for producing accurate and reliable results. Instruments such as mass spectrometers, particle accelerators, and electron microscopes often need vacuum conditions as deep at 10-8 mbar or deeper to minimize particles interfering with results. While turbomolecular pumps are normally used to attain the high- and ultra-high vacuum levels, they need a backing pump, also referred as a roughing pump, to generate the needed foreline pressure for the turbo pump to function. This article will cover key consideration for selecting a backing pump as well as going over several vacuum pump technologies that can serve as backing pumps.
Key Considerations for Selecting a Backing Pump
When selecting a roughing pump for a high vacuum system, several important factors must be considered. The pump must meet the foreline vacuum needs of the turbomolecular pump to ensure it functions properly and meets the instruments high vacuum requirement. Ensuring adequate pumping speed is also an important consideration to ensure the roughing pump can handle both the initial pump down of the system’s volume as well as the gas load during operation. Additionally, the roughing pump should produce a clean vacuum free of hydrocarbons and particulates to prevent process contamination leading to accurate results. A reliable pump with minimal maintenance requirements is crucial for continuous operation without frequent interruptions or downtime. Low maintenance needs are essential to keep operating costs to a minimum. Furthermore, the pump should produce low vibrations to avoid disrupting sensitive equipment, reducing the need for frequent readjustments.
Types of Roughing Pumps
Several pump technologies can serve as roughing pumps for turbomolecular pumps, each with its unique advantages and limitations. Rotary vane pumps offer a very good ultimate vacuum often down to 10-3 mbar but require frequent maintenance for oil changes and rebuilds, as well as the potential of oil backstreaming into the application, which can interfere with results. Scroll pumps utilize oil-free technology and provide a good ultimate vacuum typically down to 10-2 mbar but require frequent maintenance to replace tip-seals, which also poses the risk of process contamination due to tip seal abrasion. Diaphragm Pumps use oil-free technology, eliminating the possibility of oil backstreaming, and offer low noise, low maintenance with long service intervals, and a moderate ultimate vacuum typically below 1 mbar. However, it is important to ensure the diaphragm pump meets the foreline pressure requirement of the tubomolecular pump. Screw vacuum pumps are an oil-free technology with low maintenance requirements and depending on the model, can generate vacuum down to 10-3 mbar range.
VACUUBRAND VACUU·PURE Dry Screw Technology as a Backing Pump
Among the available technologies, the VACUU·PURE dry screw vacuum pump stands out as an innovative solution. Its operating principle allows for contact-free rotation of the spindles, enabling the pump to operate oil- and abrasion-free. This design eliminates the risk of process contamination with oil and particulates. Additionally, the absence of wear parts reduces operating costs, minimizes downtime, and allows for continuous operation, an important feature for high vacuum systems. Its low vibration also ensures the stability of sensitive equipment, making it an ideal choice for high vacuum applications. The VACUU·PURE 10C version is designed with chemically resistant wetted materials for processes that handle aggressive gases.
Use cases of customers using VACUUBRAND pump technology
Institute of Radiation Physics at HZDR
The Institute of Radiation Physics at HZDR operates a superconducting electron linear accelerator, which they use to explore new materials for semiconductor technology and methods for cancer therapy. They were able to test the VACUU·PURE 10 in various processes for their accelerator including to evacuate the two cubic meter isolation volumes of the accelerator module as well as a backing pump for various turbomolecular pumps. The VACUU·PURE offered exceptional performance in terms of ultimate vacuum and pumping speed as well as not generating particles due to the abrasion-free design.
University of Alberta in Canada
The University of Alberta in Canada operates an ion microprobe utilizing ion mass spectrometry. Vacuum is essential to avoid ions colliding with molecules in the atmosphere that can degrade the instrument’s performance. The initial attraction to the VACUU·PURE was the lack of contact seals, which is one of the main causes in time and expense in maintenance for them. They also wanted to avoid particulates and oils that could potentially back stream into the instrument. The VACUU·PURE is living up to their expectations and really exceeding them.
Ruhr University Bochum
Ruhr University Bochum manufactures semiconductors using molecular beam epitaxy (MEB) and focused ion beam implantation (FIB), which require ultra-high vacuum. They use VACUUBRAND MD 4 NT diaphragm pumps as fore pumps for their turbomolecular pumps. These pumps operate relatively quiet and can run for several years without issues, as well as meeting the lab’s oil-free requirement.
Conclusion
Selecting the appropriate roughing pump is crucial for the efficiency and reliability of a high vacuum system. Each pump technology has its advantages and limitations, making it essential to consider the specific requirements of the application. For processes that require a foreline pressure down to 10-3 mbar, the VACUU·PURE dry screw technology offers an ideal solution, providing clean, reliable, and low-maintenance operation, as demonstrated by its successful implementation in various research institutions and laboratories. When choosing a roughing pump for high vacuum applications, careful consideration of these factors will ensure optimal performance and efficiency of your process.
