Yes, the cover should just pull off - no part of the pressure screw mechanism should retain the cover.. the pressure adjuster is sealed against the cover with an O ring but the only part of the pressure adjust mechanism that attaches to the cover is more of a flat disc (inside) than a shaft.. The disc may be stuck in the cover slightly due to the O ring but between the the disc and diaphragm there is pretty much only a spring - The pressure adjust allen / torx screw will probably be retained in the cover when the cover comes off and not affect the cover coming off. Increasing pressure setting will put the spring under more tension and could aid getting the cover off. For re-assembly, on the one hand decreasing reducer pressure setting lowers spring tension so can make the cover easier to refit, on the other hand a setting other than minimum pressure can help you locate the spring properly (but keeping spring located properly while putting the cover back on isn't as tricky on these reducers as it is on some reducers anyway). When the cover comes off you'll see how the pressure adjust mechanism works, since you've been turning the pressure adjust screw it would be a good idea to make sure threads in the disc will/are engage(d) before bolting covers back in place, as turning the adjuster too far can cause the threads to completely unscrew coming off the threads (again the threads don't in any way hold the cover to the unit).
VSI reducer £25 in need of repair http://www.lpgforum.co.uk/viewtopic.php?f=29&t=14155
, got a few myself too!
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