If your furnace blower fuel pump is 100 psi + what should be the requirement's for an Oil Safety Valve pressure limits and what is the normal size of fuel lines for a single line furnace I'm thinking 3/8 ?
The normal size depends on the pump, how far from tank, how much lift, size of nozzle/firing rate. Oil safety valve goes on the tank to prevent the tank from leaking in the event the oil line breaks, preventing gravity flow from empting the tank.
The oil safety valve isn't under pressure, so I don't know what you mean by 'pressure limit'. A vaccuum allows oil to pass.