Boiler Safety Valve Setting

Boiler safety valve setting detailed calculation - 10-10-2010, 15:57 Boiler safety valve is set to lift at any pressure, but not more than 3% above working pressure. Also the safety Valve re-sits at 5% below working pressure. There are 2 safety valves. Both the safety valves are to be set at a pressure not exceeding 3% of the normal working pressure (stamped on name plate). Let us say the working pressure of the boiler is 7 bar. 3% of 7 bar is (7+0.21) = 7.21 bar. which means, both the safety valves have to be set at a pressure not exceeding 7.21 bar.  Apart from that, let us say one of of the valves have been set at a pressure say 7.15 bar (assuming two digit decimal even though the practice is not referring to 2 digits), then the other valve must be set at a pressure range of 10% within this. i.e the other valve setting must be 7.16 bar. I used two digit decimal only for understanding the precision of calculation. The second safety valve must be set within 10 % of the setting of the first safety valve. If any one has any other understanding please do discuss.