An existing bulk LPG system covered by GSUIR is served by a number of regulators, newer ones have OPSO/UPSO valves, older ones do not. The aim is to replace all non OPSO/UPSO regulators within a four year timescale, is this acceptable or does the replacement programme need to be accelerated for legal compliance to be maintained? Not a gas expert by any means and really struggling to find a definitive answer to this one; sources of reference that frame answers given would be really helpful for my own understanding. Cheers.