Acecare tank valve and o-rings

Folks,

For those with the double red knob/valve setup. What is the deal with the included bag of o-rings? 

Are they spares or needed for initial install? The black o-ring in the upper left of the bag looks like it fits in the space just above it, but why would only one need to be installed and the others already on? What are the white ones for? Sorry and Thanks guys

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