Better to have a strong pump and not use all the power than to be underpowered.
You must have sufficient water pressure to fuel the spray bar because washing your gravel completely clean of any fine and flour gold is of maximum importance!
You can always go with a larger pump and vary the speed as well as use a valve to control the water volume.
I am able to run a high volume of water through my trommel and still capture the fine glacial gold common to the northern states due to my sluice design.
I am using "Clarkson Riffles" ( 1" tall 2" apart) over black vortex mat with a "rubber flap" at the sluice entry to knock down any flour gold.
Believe it or not the Clarkson riffles are designed to be most efficient with a 3" per foot drop, coupled with a fast water flow.
The flour gold (or any size for that matter) typically will not make it over more than a couple of the 1" vertical riffles and the vortex mat is like a gold magnet, once the gold hits the mat it's trapped there. The only draw back to the Clarkson riffle design is that you end up with more concentrates to process than with shorter riffles, but I feel the difference in performance justifies the trade off.
Here is an example of fine and flour glacial gold taken from a creek in Indiana with my DIY 15" trommel....
Be sure and post photos of your build, it would be great to see it.
Go for the gold!
GG~
