Performance Testing of a Potential Replacement for Normetex Pump

Normetex® Model 15 scroll pump backed by metal bellows (MB) pump made by Senior Aerospace Inc. has been the preferred technology for use in tritium facilities world-wide. Normetex pumps are no longer available and identification of alternate pumps is required for performance and compatibility with tritium gas. Many of the pumps that could be used to meet the functional performance requirements (e.g. pressure and flow conditions) of the Normetex pump have features that include the use of polymers or oils and greases that are not directly compatible with tritium service. Though they are less desirable, alternative pumps may be used in tritium service with appropriate engineered controls to mitigate the impact of degraded organic compounds. These alternative pumps require characterization for potential application in tritium service.

One pump that has been identified as a potential replacement for the Normetex pump in some tritium service applications is the Edwards nXDS15iC. A series of pump tests were completed using this pump as a candidate replacement pump. The purpose of the pump testing is two-fold: (1) obtain baseline vacuum pump characteristics for the replacement pump intended for use in tritium service; and (2) verify that low pressure hydrogen gas can be transported over various distances up to 92 meters (300 feet) by the candidate pump. A series of pump tests were performed at various configurations using hydrogen gas (no tritium) and nitrogen to ensure that this pump can meet the performance requirements.

The Edwards pump meets the desired functional performance requirements, though there are other tradeoffs that must be considered. As for cost considerations, the Edwards scroll pump costs about ten (10) times less than a Normetex-equivalent scroll pump, which would significantly reduce initial start-up costs in a facility. However, the lifetime of the Edwards pump in a nearly pure tritium process stream is speculated to be only 3–6 months due to the polymer tip seals, whereas the all-metal Normetex pump can last for 5 years. Each application must determine whether the alternative pump considerations outweigh the cost differential. This paper summarizes the results of the tests that have been performed using various pump configurations.