This will be a pretty straightforward task for the right person. I have limited the budget for the project to 100 USD, so if you feel its more work for you - you are probably not the right person for the job. Here is what I need :-
I need a pressure regulator (simple spring operated or pilot operated depending upon the following parameters), to regulate a maximum pressure of 1 MPa (approx 10 bar) to a constant pressure of [url removed, login to view] MPa (2.5 bar), the mass flow remaining constant through the regulator (valve).The fluid will always be n-Butane. I will need basic calculations for the design, in case the fluid needs to be changed.
I prefer the design be in Solidworks (If you have skill in designing the right product, this requirement can be waived).
I would really like to get some fair idea that you can do the job (helps lessen time wastage), so ask some right questions in PMB.