oric_dan(333):
That site is very useful. The result with those numbers is not very good, so needing something more like
Fpwm=10Khz, Fc=100Hz, or 100:1 to get low ripple.5K and 10uF -> F3db = 3.18 Hz, which is quite low, but probably ok if all you're doing is changing slowly.
My suggestion was 100K and 1uF, giving F3db = 1.59Hz and time constant = 100ms. I guess we need to know how fast the OP needs to move the valve.