Here's a post I made a few years ago about this valve. There, I ended up with
Cv = 0.395 at 25°C and 60 lb/in
2 for the Festo VPLE18-M5H-4/2-1/4 (using SI conversions). Today, re-doing the calculation, I got
Cv = 0.407 (using Imperial, unconverted). Would someone care to read up on the calculation method (linked in the previous post, and in the attached spreadsheet) and verify the numbers?
All of this assumes that
Cv (flow coefficient) is calculated at the as-used pressures. If the manual's
Cv limits apply at the valves' maximum pressure ratings, or at the manufacturer's chosen measurement conditions, they may not match what I did above. (
Cv at the valve's maximum pressure rating is most generous for the teams. If inspecting and faced with a spec sheet for an unfamiliar valve, I would instruct the team to calculate it this way, to use the most lenient interpretation given the ambiguity.)
For reference, for this valve,
Cv at 25°C and 120 lb/in
2 (which the valve should never see in FRC service) is 0.219. At 100 lb/in
2 it is 0.265. I don't actually know the pressure rating of this valve, but seem to recall that some Festo valves were only rated for something near 100 lb/in
2, and received special dispensation from FIRST.
By the way, there was some sort of
controversy about calculating the flow coefficient in
Machine Design. I never really figured out the implications of that.
Finally, for completeness, here's another version of the valve's spec sheet:
http://www2.usfirst.org/2005comp/specs/Festo1.pdf. I believe that's the old one, describing only one of the possible wiring patterns.