Here is your answer Dutch.
Now, realize of course that every operator has different philosophies with regard to aircraft ops and such.....but a reason for always keeping the #'s 1 and 4 xfeed valves open (in this case both) is because if you lose power or the valves somehow stick in the closed position, there is no back door way of moving the fuel out of those tanks. However remote the possibility, it still exists, so that is a good reason to keep both of them always open.
Now here is a follow up question to all yous guyz....what does the blue light near the xfeed valves tell ya?......yes any boeing guy can tell you that it is an in-transit light, but what specifically is it telling you that is in-transit?
is that light responding to the sensor on the valve itself?
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think about it below scrolling down for the answer
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the answer is no. the sensor is on the drive mechanism which drives the valve. The drive mechanism is outside the fuel tank, while the valve is inside the tank, this makes replacing inop drives much easier without having to mess with fuel tanks. So this light actually tells you if the drive mechanism is actually working or not, and also indicating that the valve itself could be stuck in an intermediate position etc etc......kinda like those pesky leading edge lights.......it only takes one sensor to not make to make that pesky amber light come on.
yea yea, i know splitting hairs here with this one......but since we are hangering flying!