And you find that odd ?
They are NOT a pressure accumulator, they control pressure when being faced with a higher pressure they let the excess go so maintaining what they are set to.
They will not, AND DO NOT NEED TO hold pressure for hours, unless you want to run a engine with no fuel pressure ?
I have a brand new RS500 one on mine, and that acts the same, the ecu primes first thing in the morning it would not need to if they held pressure, presumably they do this as the makers know they don't hold presssure ?
The prressure will subside back into the tank through the pump when off due to thie pump design, same as they can run backwards, do this to clear them out as well.
tabetha