Is there such a thing ?

[Sharon the Cat]

We have just had an auto-changeover valve fitted on the cottage cylinders. You leave it set to one cylinder & when that runs out it pulls from the other one but shows a red marker to tell you that tank is empty. Then you swap the tank & switch it to the other tank & wait for the red marker again. That way you only have to check every so often & will know if one tank has run out.