Where a valve is needed for regulating the pressure inside a process. The issue is that the pressure setpoint.Varies quite a lot. The valve(s) is installed downstream of the process, and the process itself has inlet flow controlled. The minimum flow is on the order of 10% of design flow, max flow 120% of design. Pressure setpoint can vary anywhere between 3 barg to 8 barg. Following on valve selection: a) The best test for all valve selection is to give a complete perofomance requirement description, including pressures before and after  gas valve, fluid and flow descriptions, temperatures, operation, certificates and tests, actuation and operation details, closing and opening times etc. etc. In addition give a sketch of required deliverytimes, expected lifetime and number off. b) Second step ask two or three quality valve suppliers for a preliminary offer including alternatives and suggestions. c) Base your official inquiry on what you have gathered of information on commercial available solutions on this. d) On the small sizes you mention a standard valve with variated trim or special types may cover your total requirement. Following on regulating purpose: aa) In processes regulating requirements are often set 'too fine' complicating the process control. Be sure that the valves actually are necessary. bb) Same as above: check other cheaper solutions for control cc) I have seen alarmpoints in processes set too fine, or to react too soon, and process extra controls then required not to release the fine alarmpoint. Be sure this is not the case. dd) I have on steam seen unnecessary double controls, for instance outlet and inlet, working against each other, keeping heat exchange surfaces half drowned in condensate in stead of free against steam, reducing heat transfer to much less then half capacity. Any similarity? ee) Possible swinging curve in regulation if inlet and pressure control not properly damped or tuned too fine?

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