Surely the reason there isn't a NRV in the supply tank fuel line is because if there was, not only would we have to continuously have the prime pumps on, if it was to stick, the respective engine would cut off! Nothing to do with drain back!
???? I think this is nonsense; I should think that the main reason for
no NRV is, that as long as the respective engine is running the engine driven fuel pumps are maintaining the fuel feed to the engine by means of suction...thats the reason why you switch the prime pumps off after the fuel flow has been well 'established' (engine started). Even if a NRV was installed in the feed line, the engine pumps need to 'suck' just a little harder to overcome the springload of the NRV. No need to do that.
So, NO, you wouldn't need the prime pumps continuously,
and suppose the NRV stuck in closed position....that can only happen in an engine off situation, and you wouldn't be able to start the engine......stuck in the open position.....you wouldn't notice the difference.
And also SS,... i've been reading a lot of posts of you lately, and also quite some replies to your posts, and I believe I've come across the word 'arrogance' more than once. Must be a reason for that
....and as to why the main tank continues emptying into the supply tanks for some time after shutting off the XFER Pumps...I don't know, but witnessed it on two machines.