While refilling the hydrogen system after an outage caused by a power failure, the excess flow valve located at the hydrogen tank tripped, but did not go fully shut.
The large valve is equipped with a small bypass valve so that the valve can be pressurized on both sides as is required before the valve can be reset. The O-ring which makes this small valve gas tight was deformed and improperly seated, thus allowing gas to flow to each side of the large valve. This permitted the valve to trip normally, but not to seat properly. The following is the manufacturer's evaluation after disassembly and inspection of the valve.
This valve was recently installed to provide excess flow protection to the underground portion of the hydrogen system piping and to provide redundant view more