Although your system has a pressure less than atmospheric, the principles of pressure loss and its calcullation are the same as a "pressurized" system. You need to calculate the line velocities and line fluid densities, calculate the velocity head and multiply be the "k"...
The most appropriate codes and standards is usually a function of what you are specifying. Ultimately you, or your customer, have to decide on the governing standard.
I am on boards for ASME and ISO with respect to flow measurement. ASME (like the rest of the world) is leaning toward...
The cost of adding a diffuser to a PTC-6 nozzle is pretty insignificant: Depending on the size, you might be talking about a couple of percent. Depending on your flow characteristics, there are a number of methods to reduce permanent pressure loss.
David Wyatt
Wyatt Engineering
401 334 1170...
