These regulators ensure first stage pressure reduction and a continuous gas supply to the installation. This valve switches to your reserve cylinder should the supply cylinder pressure drop. The indicator arrow turns red when the system has changed over and points to the empty cylinder. The indicator turns white when turned towards the new service cylinder. Twin stage/twin cylinder installation propane gas regulator kit. For use with cookers, hobs, gas fires and ovens and the likes. UK Gas Safety Regulations state that in any domestic installations of over two cylinders an OPSO device is required.