Riffle size?

[KurtB]

I am going to modify my sluice to a highbanker. The riffles are 3/8" high. Do I need to increase the size of the riffles to work with the increased water flow? Any suggestions on a good grizzly design?

Thanks

Kurt

[kiwi jw]

3/8th" high riffle is a pretty small riffle for any type of recovery system.

JW

[Hoser John]

You have low velocity riffles in a sluice L shaped and in a high velocity hi/b you utilize modified hungarian riffles which are reversed. Then you must dump the expanded metal as the L lip is not at the top and the thin edge does NOT seal anymore so you lose your gold through the gaps. Turn on a flashlight in the dark and looksee--bummer ain't it. Anyhow-width of sluice--hp of motor and size of pump are your determining factors to riffle construction in height and angle too. Post more--John

[KurtB]

Thank you for your replies.

Kurt

[kiwi jw]

Hi there Kurt, If you want to use expanded mesh under your riffles, as hoser john says you will get a little gap under the riffles where it straddles over the mesh & that will allow water pressure under the riffle & so help in washing out the material that is supposed to gather on the down stream side of the riffle. One way around that is to use a riffle shaped like this with a big foot at the bottom that will span that gap in the mesh & cut off the water from going under the riffle as long as the riffles & mesh are tight down onto the carpet or matting. These riffles are 3/4" high







A highbanker doesnt need to have an aggresive flow of water down the box. Especially if the material has been pre classifyed. The only reason you need a strong flow down the box is to wash on & out the bigger stones that you shovel or dump into it. The more gentle the flow the better your fine gold recovery is going to be & the stronger the flow the more chance of losing finer gold.

This is probably a bit strong a flow for this short box, notice the white water over the riffles, but I needed the stonger flow to run the suction nozzle. The gold wasnt very fine & I didnt appear to lose any.







When I use this set up as a highbanker/banjo I only need to run the motor on start up idle only & it gives plenty of squirt in the water jets & will run for hours on one tank of gas. The water flow is enough down the box to was on the material & very good at fine gold recovery. You will see the difference in the water flow over the riffles. A lot more even & smooth with no white water.





Fine gold recovered



My sluice box I run a smaller riffle of about 1/2" high with a 28 degree slope, not 45 degree & spaced further apart. More for low flow & lower velocity of water. It gives more time for fines to settle out. I generally pre classify the material to aid in the gentler flow & still allow the water to wash on the waste material without having to help it through.



Pre classifying material in my sieve buckets



Ready to feed the sluice with the pre classifyed material



Feeding sluice



Wash up



Result






happy hunting

JW

[russau]

kiwi i would think it would be advantagious to make thar riffel system so that you could flip it over and use the deeper riffel also on your highbanker.just a thought.

[Tarkus]

JW: Great post, I build most all of my own equipment and as soon as I can get the program working again I'll post some of my project pic's.

[DanB]

B e a u t i f u l ............look at all that yellow stuff...... keep up the good work....and tones of AU to U.

db

[KurtB]

Thanks for all the pictures and advice. Seeing all that gold really gets the fever going.

[russau]

Kurt for the size of the gold your getting in Nebraska a small riffel will work fine for you! but youll need to controll the water and your feed and keep anything from slipping underneath your riffels. if .like Hoser said, if you can see ANY light underneath the riffel, youll be losing your fine gold for sure!.on my dredge ,i weld the expanded screen to the edge of my riffels so that when its clamped down, everthing goes down against my mat/carpet/miners moss or what ever i use to help collect the fine gold. large riffels are fine if your getting any nuggets. but for fine gold ,the trubidity/bubbles of the water will flush out that midwest glacial gold!

[KurtB]

South Dakota and Colorado are the only places that I have been. I prefer South Dakota because I have found more flakes and small pickers. It's about an eight hour drive one way to both places so I can't even be called a weekend prospecter. I have attached some pictures of my sluice and home made hopper/grizzly. It's not quite done yet but it seems like it will work fine when finished. The 12 volt pump is 2000 gph and seems to be just about right.

Thanks again for all the advice.

Kurt

[Vance in AK]

You guys build some great highbankers! Insperational you are

Hoser, thanks for answering a question I had before I even asked it (You must be psycotic or something! ). I was assuming I needed to remove the expanded metal from my A-52 highbanker/2.5" dredge conversion now that I was finally getting around to putting in the dredge/highbanker riffles. I've used it for years with the original (only a few times a year) so I guess it's about time. Lowered the angle of the grizzly so it doesn't shed material quite as fast. I also put a plate in the hopper that directs the slurry to the very top of the sluice rather than dumping it straight down. Punch plate for the 1st foot of the sluice, then about 8" of nothing(but carpet), then the riffles. Ribbed carpet from one end to the other. Need to put in a light rubber flap near the top to smothe the flow a bit.
I will be running my new Honda WX-15 unless we are using my old 2" dredge at the same time, then the highbanker will get the old 3hp BS with 2" trash pump.
Any other suggestions for mods? Not much big gold here on the Kenai, but some pickers & small nuggets.
Also thinking of converting the little 2" dredge (It's an old Keene, the floats on 1 innertube type) to a very backpackable dredge/highbanker unit along the lines of JWs using the WX-15. A WX 10 might work too but I don't know if it will run the 2" dredge with the standard Honda pump. I hear the WX-15 will run a 2.5" & one guy said it will run a 3" in shallow water but I ?? that.

By the way, not trying to hijack the thread but figure the info applies to original poster too.

[Goodyguy]

This is what I learned yesterday at the GPAA gold show. Sluices are not made right!
They are best at placer gold recovery, but share a common design flaw that reduces maximum gold recovery.

The purpose of a sluice is to separate all sizes of gold from the other material such as gravel, sand, dirt, etc. trapping the gold and eliminating the waste.

To achieve that task a sluice needs to:
Create the proper vortices to allow the different sizes of gold to separate and drop out of the water flow to then become trapped for recovery.


Here is the main design flaw in sluices: The water flow over the riffles is going the same speed as the water flow over the expanded mesh. Because the expanded mesh is located in the same part of the sluice as the riffles there is no way to adjust the water speed separately. * see below.


Expanded mesh is best at trapping small or fine gold. But for the proper vortex to form, the water speed needs to be a lot slower than for riffles.

Riffles are best at trapping larger gold but to form the proper vortex the water speed needs to be a lot faster than for expanded mesh.

Riffle height should be no more than 1" tall and then the top lip not extend forward more than 1/2 inch and the 1/2 inch lip should be elevated 15 degrees above perpendicular to the sluice box and the riffles should then be only 2 inches apart. any more or any less apart will not create the optimum vortex.

Here is a link where this info may be verified : http://ygsftp.gov.yk.ca/publications...errecovery.pdf


Go for the gold!

GG~

*To overcome this problem, a proper sluice design would have to have a way for reducing the water speed over the expanded mesh while allowing faster water speed over the riffles. But how do you achieve that and still be able to keep the sluice clear from building up too much material at the slow part?

Can a sluice be designed to eliminate that problem?

[Astrobouncer]

Riffle height should be no more than 1" tall and then at the top not extend forward more than 1/2 inch and the 1/2 inch part should be elevated 15 degrees above perpendicular to the sluice box and the riffles should then be only 2 inches apart. any more and any less apart will not create the optimum vortex.

GG~

This supports what my own testing shown in the field. I tried 6 inch, 4 inch, 3 inch before finally settling on 2 inch on the sluice I use now. The further apart the riffles were, the more they backed up.

[Goodyguy]

Riffle height should be no more than 1" tall and then the top lip not extend forward more than 1/2 inch and the 1/2 inch lip should be elevated 15 degrees above perpendicular to the sluice box and the riffles should then be only 2 inches apart. any more or any less apart will not create the optimum vortex.

GG~

This supports what my own testing shown in the field. I tried 6 inch, 4 inch, 3 inch before finally settling on 2 inch on the sluice I use now. The further apart the riffles were, the more they backed up.

Now I know why mine have been getting clogged and why I also had to keep a bucket at the discharge end of the sluice to catch the lost gold. And I could never get the angle of the sluice or the water speed adjusted to prevent it.

Not only are my riffles too far apart they also do not have the correct angle at the lip to create the proper vortex.
I will definitely redesign my riffle setup before my next trip out.


GG~

[Shake n Flake]

*To overcome this problem, a proper sluice design would have to have a way for reducing the water speed over the expanded mesh while allowing faster water speed over the riffles. But how do you achieve that and still be able to keep the sluice clear from building up too much material at the slow part?

I can think of a couple ways to do this. One could make the mesh area wider than the riffle section; the same amount of water, moving over a wider chute covered in miners moss, would move more slowly. Another would be to hinge the sluice, allowing the riffled area to be set at a steeper angle than the mesh/moss part.

[Goodyguy]

*To overcome this problem, a proper sluice design would have to have a way for reducing the water speed over the expanded mesh while allowing faster water speed over the riffles. But how do you achieve that and still be able to keep the sluice clear from building up too much material at the slow part?

I can think of a couple ways to do this. One could make the mesh area wider than the riffle section; the same amount of water, moving over a wider chute covered in miners moss, would move more slowly.

We are thinking alike.

I thought of doing that also, but in practice wouldn't the extra material just build up at the slow part and not be washed down and out of the sluice?

Another would be to hinge the sluice, allowing the riffled area to be set at a steeper angle than the mesh/moss part.

I also thought of that idea but still can imagine the build up of material at the slow section.

The catch is: Keeping the material moving fast enough to keep it from building up where the waterspeed slows down to allow the proper vortices to form over the expanded mesh area.

Whether the slow section was first, in the middle, or at the end, it would still create a bottleneck causing the material to build up due to the slow water speed.

Perhaps I am over thinking the whole thing and should just be happy with the compromise that is currently being used.
I always keep a bucket under the discharge end anyway.

GG~

[Goodyguy]

*To overcome this problem, a proper sluice design would have to have a way for reducing the water speed over the expanded mesh while allowing faster water speed over the riffles. But how do you achieve that and still be able to keep the sluice clear from building up too much material at the slow part?

I can think of a couple ways to do this. One could make the mesh area wider than the riffle section; the same amount of water, moving over a wider chute covered in miners moss, would move more slowly. Another would be to hinge the sluice, allowing the riffled area to be set at a steeper angle than the mesh/moss part.

Would you put the slow part toward the top end of the sluice or at the bottom end?

[Goodyguy]

Riffle height should be no more than 1" tall and then at the top not extend forward more than 1/2 inch and the 1/2 inch part should be elevated 15 degrees above perpendicular to the sluice box and the riffles should then be only 2 inches apart. any more and any less apart will not create the optimum vortex.

GG~

This supports what my own testing shown in the field. I tried 6 inch, 4 inch, 3 inch before finally settling on 2 inch on the sluice I use now. The further apart the riffles were, the more they backed up.

Riffles too close together or too far apart creates packing.





Ideal

[strickman]

or the dovetail box/sluice design with riffles in the upper section , expanded on the lower -wider section = slower water .