Hydrogen valves for your H₂ applications

In gas system operations, pressure differentials can often occur at the valve, resulting in a higher pressure at the valve outlet than at the inlet. A so-called back pressure (pressure higher at the outlet than at the inlet) can cause the valve to open against the flow or inadvertently slow down the closing process. Direct-acting or force pilot operated valves provide greater back-pressure safety thanks to their strong closing springs. The EN 161 standard offers a good grounding in the subject of back-pressure safety and valve classes.

In many applications, the ambient temperature plays a less significant role. If the ambient temperature rises above 50 °C, you should examine whether the solenoid valve is appropriate for these temperatures on an ongoing basis. The copper winding of the coil reacts to increasing temperature with an “increased” resistance. This then means a reduction in output and performance. In confined spaces, and with sound insulation and functional protection of hydrogen systems, heat build-up can lead to a reduction in performance and therefore functional limitations. 

The compact design of stationary fuel cells as well as their close proximity to the stack can lead to two challenges. On the one hand, there is the ambient temperature, which is higher than usual, and on the other hand, the large number of process interfaces. Each interface, by itself, represents a small potential hydrogen leak, the consequence of which can be accumulation of hydrogen. Because of the diffusion and temperature aspects, customers and/or testing authorities often define stack control as ATEX Zone 1 or Category 2.

The Joule-Thomson effect is a physical phenomenon that occurs when a gas expands through a choke without exchanging heat with its environment. This leads to a temperature change in the gas. With the Joule-Thomson effect, a gas can either increase or decrease in temperature, depending on its Joule-Thomson coefficient, for which the starting point is the inversion temperature of the gas. In the case of hydrogen, the inversion temperature is > -80 °C. Hydrogen therefore warms during expansion.

Particles inside the system can lead to unintended leaks. Regardless of whether the hydrogen is pure, the system must be cleaned and purged before start-up. Even the smallest of particles damage not only the stack, but also the hard but sensitive seal surfaces of the valve seats. To prevent upstream contamination during refuelling or servicing, install filters in the systems.

Control valves are placed under particularly high demands in hydrogen applications. They must withstand pressures of up to 40 bar, as well as operate safely at high temperatures. The relationship between pressure and temperature is of particular importance when it comes to the control of gases. For example, in order to maintain oxygen in a gaseous state, the temperature must be lowered when the pressure is increased. The ideal gas law describes this pressure-temperature relationship of gases. Thus, an increase in pressure at constant gas quantity and constant volume leads to an increase in temperature, and vice versa. 

Unlike in other applications, the production or use of hydrogen requires an especially high level of valve tightness. If leaks occur, this presents an extreme hazard or reduces the efficiency of the system. Control valves therefore need to have a tightness of 10^–4 mbar∙l/s.

• ISO 15848 – Defines test procedures and leakage classes for industrial armatures and valves
• Directive (TA) – Air – Regulates emissions from industrial plants
• ATEX – Certification for components used in potentially explosive atmospheres
• ASME B16.34 – Sets requirements for valves in pressure applications
• PED – Regulates the design and use of pressure equipment, including valves
• Manufacturer's Declaration – Certifications from valve manufacturers regarding performance, quality, and reliability