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 0.25 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.
The pressure regulator will have mass flow rate is 5e-8 kg/sec.