Mahmood: Is the pump a positive displacement pump with a pressure relief bypass or is it a pressure limited pump?
in either case you must return the excesss fuel to the supply tank, the energy wasted will convert to heat so you do not want to return to the pump inlet. Raghunathan's site has a good solution provided it is fast enough with the rest of the fuel system in the loop. In fuel systems the parameters are carefully selected so that at max output there is minimal spill back fuel. The rest of the system is set up for minimal fuel under pressure to limit the amount of energy that needs to be controlled and minimise response time. When you select a control valve confirm that it will work correctly with the fuel that you will be using and at the filtration level you are using or you may have a catastrophic valve failure. If the flow rate required is low enough and the fuel is kerosine or diesel an automotive fuel repair shop may have a fuel metering valve from a diesel engine that could be adapted should the cost of the flow valve be to high. Terry