BBforks,

The lst time I went on a gas course was back in 1980, you appear to have to standards over there, from what my notes tell me our LPG consist of one standard that it conforms to and that's BS 4250.
LPG dose not have any additives and reclamation oil part of the processing system and is deposited in the regulator when LPG is fed to the engine ie sludge and heavy ends I refer to the stuff.
The benefits of running an engine on LPG and I'm sure you know them,
1 less engine wear
2 engine oil life extended 400%
3 smoother engine running due to LPG being over100 octane s
4 less spark plug wear.
5 les Co Co2 emissions
.Filters over here usually are of two types a solenoid type magnet for trapping iron filings that come out of the tanks, very fine micron mesh filter as on the Cat trucks I have noticed and quite thick felt pad filters as used on Yale trucks as on the impco gas system and Asian system.

I hope this info is of some use.

Regards Titus