Lockin fuel cap - reassembly opps

[Saffy]

I renewed my crushed locking fuel cap with a new one. I wanted to use my original lock barrel as it same key for doors and didn't want an new extra key. So I took them both apart and was 'surprised' by a little glass bead, a steel ball bearing a little rocker in the new cap (the old one had lost those bits except the glass bead). Those items a seem to fit into two ports and capped by the rocker... but I am not sure. After the lock swap I have put it all back together with the glass bead in the right-most hole, the steel ball in the deeper left hole and the rocker covering the two, anyone confirm that is correct? I am guess it's a two way breather valve *shrug* or plugs hole when car rolled over ? *shrug*  there was also another brass fitting in both caps with a sprung loaded ball but not effected by changing out the barrel.

[Range Rover Blues]

Depending on model year etc the fuel capmay have a pressure biased breather with vacuum relief too, it takes a positive pressure to breath out but no pressure to breathin (controls Hydrocarbon emmisions).

[DogVanMan]

When I fill up my TD5 110 at local garage after 2 miles running, it's built up neg pressure in the tank (I think) as when i release the cap I can hear air sucking in. Can't say I notice it if I release the cap after driving a few miles.. Do I need a new cap? (Breather knackered?). No other symptoms - engine runs fine etc.

G