While filling liquid oxygen into a tank, why do they do open one end? Then what is use of filling?
I don't think people who are filling this truck are beginners. 
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7$\begingroup$ Don't you agree that in order for something to get in the tank, something should get out (to avoid increasing pressure to up levels where it wouldn't be possible to fill)? $\endgroup$ – Molx Sep 13 '15 at 4:54
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3$\begingroup$ I really hope that's nitrogen and not oxygen. $\endgroup$ – Martin - マーチン♦ Sep 13 '15 at 7:38
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1$\begingroup$ Moreover, you need to allow the vapours to get out. $\endgroup$ – WYSIWYG Sep 13 '15 at 10:16
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$\begingroup$ Releasing oxygen gas right over the exhaust pipe seems like a wonderful idea. $\endgroup$ – Marcel Nov 5 '16 at 12:31
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The end is opened to allow oxygen gas to escape. The flow of liquid oxygen into the tanker will not be pumped, just undergoing the natural tendency to flow from an area of high pressure to low pressure. As such, there would come a point when the residual gas in the tanker would start to provide back pressure on the flow input, slowing it down & potentially stopping it once pressures equalize between the tanker and the source.
By allowing oxygen gas to escape the tanker, the pressure will always be lower in the tanker, and the flow will be faster more adequately fill the tanker. The same technique is used when topping up liquid nitrogen in an NMR spectrometer, for example.
