Depending on pressure and temperature levels, Greene Tweed said it recommends special O-rings made from FKM or metal spring energized (MSE) PTFE lip seals that offer "exceptional" resistance to hydrogen exposure.
Greene Tweed is currently evaluating new sealing solutions and thermal insulation materials for extreme temperatures found with liquid hydrogen.
A further issue is that the low lubricity of the hydrogen molecule can lead to excessive wear and friction in equipment, like valves and compressors.
To address such problems, Greene Tweed offers a PFA composite with unique dry-running properties and a special cross-linked PEEK polymer material.
Looking at weight, a key issue in aircraft fuel-consumption, Greene Tweed noted that energy density of hydrogen (by volume) is around three times lower than jet fuel. Reservoir sizes must, therefore, be dramatically increased to transport the same volume of energy with hydrogen as with jet fuel.
As a lightweighting solution for hydrogen aircraft, Greene Tweed pointed to its Xycomp thermoplastic composite, which is already extensively used in the aerospace industry as metal replacement.
Carbon/PEEK composites are permeable to hydrogen due to their molecular structure and relatively large space between the molecules and the graphite planes. So, they cannot accumulate hydrogen as can be seen with metals, according to the company.
Considering that hydrogen embrittlement is therefore not possible with a polymer composite, "use of our Xycomp solutions makes even more sense in the low-carbon emissions aircraft of the future," Greene Tweed stated.