Just tried the filter.
I am guessing contains requires the whole string, I tried it for used equipment typing just part of one item and it could not find it.
I then went in to try more - entered the complete string and got nothing. Not sure what the behaviour should be (partial would be more useful) but I could not get it to work.
Numbers for size of cylinder worked fine though.
used equipment does not work well for filters. Just the equipment ID's are stored, the equipment items are in a separate table and thus the filtering does not work here. Look at the UsedEquip field in the logbook table in edit mode. You see just numbers are stored, e.g. "5,2,10".