At all, it is recommended to remove the existing regulator if it is flow rate – scale in liters / minute – especially if it has a Bourdon tube indicator (watch dial with needle). If it is to make comparative test of consumption it can be maintained but opening the step to the maximum with the Vigila as in regulator mode , in that case the measures offered by the mechanical meter or rotameter will not be correct. If it is a pressure regulator what there is – scale in bars – it will suffice to set more than 2.5 bars and prevent anyone from changing it.