www.hpmag.co.uk HYDRAULICS & PNEUMATICS November/December 2025 27 high-pressure valves are lower rated but still designed for operation up to 350 bar, for this design of valve, the tube, which is the central bore that the hydrogen flows through, is machined and welded. However, ultra-high-pressure valves require a tube that is machined and screwed. Hydrogen embrittlement The reason this reinforced design is necessary is to prevent hydrogen embrittlement. This can occur when hydrogen atoms penetrate the crystal lattice inherent to the stainless-steel construction, ultimately resulting in micro-cracks that impact the valve’s integrity. At higher pressures, the greater concentration of hydrogen molecules dissipates into the stainless steel more quickly, speeding-up the embrittlement process. Whereas welding can potentially result in weak points that can be penetrated, bolting and sealing the key components of a valve can prevent this, optimising suitability for ultra-high-pressure applications. Another area of potential weakness is the valve seat, the surface that closes against the valve tube to stop the flow and ensure a leak-tight barrier. At pressures up to 1,000 bar, this dynamic sealing point requires a design that can achieve seat leakage as low as 0.0001 ml/s (millilitres per second). This level of tightness can be achieved with precise techniques including a dynamic sealing ring on the spindle. High-resistance seals In combination, for ultra-high-pressure hydrogen applications, the material construction of the seal, which sits against the seat to create the final barrier, is critical. Even at low pressures, hydrogen penetrates elastomers, a typical seal material, resulting in trace permeation of the gas. More seriously, however, is the damage caused to the seal as a result of hydrogen absorption. When there is a sudden drop in pressure, caused by the high differential during the switching process, the force of the hydrogen expulsion during decompression will damage the elastomer and degrade its sealing capability. This is evidenced by bubble formation on the seal. As a result, polyether ether ketone (PEEK) should be used as the seal material for ultra-high-pressure hydrogen applications. With significantly higher resistance to hydrogen permeation, PEEK also retains its integrity at temperature extremes down to -40°C for hydrogen precooling before dispensing, as well as +80°C which can be reached during compression. The importance of inspection Even when high-strength design and construction, combined with durable materials, is applied to the valve body, seat, and seal, an inspection programme is essential to maintain safety and flow performance. For example, my company’s valves’ design for high-pressure and ultrahigh-pressure applications, inspection is recommended between 80,000 to 100,000 switching cycles. A special inspection hole at the sealing point also enhances ease and speed of any potential leak detection. While PEEK seals can be replaced. [1] https://drivinghydrogen.com/2025/0 1/21/aegis-lands-100-million-to-build-30new-uk-hydrogen-refuellingstations/#:~:text=The%20investment%2 0will%20fund%20an,the%20country’s%2 0transport%20decarbonisation%20efforts Ɵ ħĦĦĦĦĶ ĨĮ Ǒ īīĦĶ ĨĦĨĬ Ɵ ƨ Ǒ Ǒ Ǖ īīĦ ǒ ǒ Ǒ Ǡ Ǖ ǚ ǒ Ɵ ǒ ǒ ǒ Ǖ ǒ ǒ ƨ ǎ Ǒ ƨ Ǖ Ǒ Ǒ Ǖ Ǒ Ǖ ǒ Ǖ Ǒ ǚ ǒ Ǒ LjǏ ƠǕ ĶĪĪ ƮĦƯĨĦ ĩħįĬ ĪĪħĪ
RkJQdWJsaXNoZXIy MjQ0NzM=