Lab update – Polymeric Compensator Test Campaign with Daniel

In this month’s lab update, we look between the tubes. A reliable connection between pipe sections is essential. The connection must be able to cope with temperature induced changes in the material and at the same time guarantee air-tightness. This connecting element is one of many mission-critical elements needed to build our DemoTube. Daniel is currently testing various designs of this connection in his experimental test stand.

Together with our partner ditec dichtungstechnik, we have developed a compensator made of polymeric material, which is to be used as an interface between tube segments. In the current test series, the aim is to check this compensator in different setups. On the one hand, we test the connection with different pipe materials, for example concrete to steel. And on the other hand, we experiment with different sealing methods. This includes tests with contact pressure, strip clamping and bonding.

Furthermore, the right coating for our steel parts is important to prevent them from oxidizing. The oxidation creates holes in the steel and could influence the air-tightness of the compensator interface. Our partner Oerlikon Metco helps us in choosing the right coating solution for our purpose, so that a good longevity can be achieved.

 * Test stand

The test stand is constructed as follows. (see picture) Two concrete pipe sections, each closed by an end cap made out of coated steel, are connected by the compensator. The various sealing techniques – contact pressure, strip clamping and bonding – can then be applied. A vacuum system from our partner Leybold is connected to the test piece and pumps out the air from inside the tube. The aim for our DemoTube is a pressure of 1mbar. These tests allow us to check and document the minimum requirement on a small scale. The pressure inside the compensator is measured through a pressure sensor. Monitoring the pressure increase over time a leakage value can be computed.

Furthermore, the permeation of the material itself can be tested. Permeation is a form of leakage and can be quantified by leakage measurements. In order to analyze the permeation of the compensator, we make use of models from literature. Complementary to leakage, this metric is key to quantifying the amount of air passing through the material since the permeation is dependent on temperature. On hot days this value tends to increase because the molecules in the material expand, leaving behind bigger gaps and thus letting more air pass through. This leads to higher permeability between the vacuum inside the tube and atmospheric pressure outside the tube and therefore to higher leakage.

These connectors are one of many essential components to make vacuum transport possible. Our focus in the development of this component remains to keep infrastructure costs as low as possible, while assuring the system itself is as robust, simple and reliable as possible.

“For our Hyperloop test facilities, we examine existing technologies from the industry. High-end vacuum-rated components are in some cases oversized, which tend to increase their price. By reviewing and selecting the right components, we can save costs and deliver an economical overall package. Thanks to our in-house experimental research, we can test, select and verify the suitable ones.”

Daniel Elmeua Lehmann

Vacuum Mechanical Engineer