Here＇s a six-step plan for using the Instrument Society of America＇s (ISA) standardized procedure to size control valves for compressible flow, ISA established a committee in 1961 to develop standard control valve sizing equations, Their efforts culminated in a procedure that has achieved the status of American National Standard, Later, the International Electrotechnical Commission (IEC) used the ISA works as a basis for international standards, Except for some slight: differences, the ISA and IEC standards have been harmonized.