HYDROGEN
the entire process less efficient . Lower-quality stainless steel components may allow hydrogen molecules under pressure to diffuse into them , causing a phenomenon called hydrogen embrittlement . If left unchecked , hydrogen embrittlement can accelerate the spread of fissures and weaken components , allowing potential leaks over the service life of the equipment .
Hydrogen valves must perform
Given the critical role of valves in a fluid system , careful consideration must be given to meeting the specifications of the application . When specifying valves for a hydrogen fuel system , operators must take the following into account :
• Pressure : To achieve the desired density , hydrogen must be compressed in on-vehicle , distribution , and refuelling storage tanks at 350-700 bar .
• Stress and vibration : Systems must be able to withstand fast speeds , bumpy surfaces , and a variety of environmental factors such as inclement weather , corrosive substances , and changes in temperature .
• Safety : Refueling stations must be safely operable by the average enduser .
• Maintenance : Technicians must be able to easily and quickly install and remake leak-tight joints during servicing . These criteria must be applied to all hydrogen valves to ensure they always perform at the highest possible levels . Leak-tight performance at the connection , shut-off , or regulation points is essential throughout on-vehicle and refuelling systems . Valves used in hydrogen fuel systems must be able to handle all the challenging operating conditions they may face , depending on the specific application and type .
Hydrogen ball valves
Hydrogen fuel systems use ball valves to start and stop the flow of hydrogen from one part of the system to the other . If ball valves are specified for specific applications , operators should seek valves with stem seal designs that will resist wear over time ( Figure 1 ). Trunnion-style ball valves with direct-load designs can be an excellent choice . Their design enables leak-tight performance each time they are activated , and each time they shut off . Alternatively , bottomloaded stem designs may prevent possible stem blowout , which could enhance the overall safety of the system . Experienced valve suppliers may be able to offer advice on which valves will work best in particular applications . Some ball valves offer two- or three-way functionality , different mounting options ,
and a range of flow coefficients that can be customized to fit specific needs . Lastly , it is important to make sure that the ball valves selected are compatible with other components within the hydrogen fuel system .
Hydrogen needle valves
When the adjustments in a hydrogen system must be more precise , needle valves may be a better option than ball valves . Like ball valves , however , it is important to consider several factors when deciding which ones to specify . Typically , needle valves are all-metal in construction and need significant force to seal properly ( Figure 2 ). If the specified needle valve is not able to withstand such pressure , it may deform the needle itself and possibly the seat , leading to potential leaks and expensive repairs . Secondarily , the pressure is usually applied by large air actuators to open and close the valves , which can cause the needle valve to be under intense pressure for as long as two minutes . To handle such operating conditions , needle valves should be constructed from high-quality 316 stainless steel , which is better able to prevent deformation during repeated use . Not all needle valves are certified to the proper pressure ratings for common hydrogen applications , which means they may not be able to
Figure 1 . To protect end users in hydrogen applications , ball valves must contain stem seals made from materials that are resistant to long-term wear . Image © 2023 Swagelok
Figure 2 . It requires large amounts of force to open and close needle valves in hydrogen applications , which means the specified valves must be able to withstand those pressures over time . Image © 2023 Swagelok
38 Valve World February 2023 www . valve-world . net