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2" dredge build - sluice box design questions?

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2" dredge build - sluice box design questions?

Postby PAsniper » Tue Mar 24, 2015 12:02 pm

Hey all... I could really use some advice from you mastermind dredgers... I am in the process of building my 2" an had some design questions... Here are a few details (and some pics attached):

52 gpm 1.5" pump
Home made 2" "infinity jet" (special thanks to Robert @ Goldsnare company)
8 foot 2" suction line
My sluice I've already fabbed is 11" wide x 33" long
I planned to have my sluice non-adjustable (drop per ft) and set at 3/4" per foot drop

My question(s) is/ are:

What would the depth of water flow through my sluice be approximately if I'm running 80% throttle? The reason is, I'm wondering if I'll have enough depth in the sluice to incorporate an over/under design. I was thinking of maybe 1/4" punch plate set roughly 3/4" high with "v-mat" in the lower section with 3/4" high riffles and moss on top. Or possibly even "gold hog" on top. I would really appreciate suggestions.... Mainly:

1) will I have the proper water depth for over/under? I'd need at least 2" water depth I assume
2) should I make the angle of my sluice adjustable?
3) if I make the sluice single stage, would 15" of punch plate over "v-mat" then 18" of moss / clarkston riffles be efficient?

Sorry for the long post, and I will update pics though out the next few weeks. Thanks in advance fellas!

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Re: 2" dredge build - sluice box design questions?

Postby PAsniper » Tue Mar 24, 2015 12:06 pm

For some reason I cannot upload pictures (I think because I'm trying to upload from my phone).... I will try later from my home PC. Thanks guys!

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Re: 2" dredge build - sluice box design questions?

Postby sanman » Tue Mar 24, 2015 7:34 pm

sniper, your requested information is one of the largest request I have seen in a very long time with so many variable answers....In MHO build a basic dredge and than tune it in and make it work just the way you want it to ....After that make changes ONE at a time to see if it helps or hurts....and ALWAYS have an adjustable sluice...hope this helps...
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Re: 2" dredge build - sluice box design questions?

Postby PAsniper » Tue Mar 24, 2015 9:02 pm

Thanks for the advice, sanman.

I am attaching some pictures for a better idea. My main question really is this: Will I have enough depth in my sluce to run a 2-stage? I would hate for my sluice to not have enough flow to wash the upper section material out (minus the gold hahaha).

Anyway, I will try to update this build with pics througout and ANY input is appreciated. I am very open-minded, especially when getting info from you all... Thanks!

Rich

IMG_1378.JPG
Float and Pump
IMG_1378.JPG (222.25 KiB) Viewed 6881 times


IMG_1379.JPG
Float, pump, sluice
IMG_1379.JPG (223.94 KiB) Viewed 6881 times
Last edited by PAsniper on Tue Mar 24, 2015 9:03 pm, edited 1 time in total.
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Re: 2" dredge build - sluice box design questions?

Postby adawg » Wed Mar 25, 2015 4:05 am

Without actually putting the dredge when completed, in the water, filling the box with water, it is difficult if not impossible to calculate what your
final angle of sluice will be . The weight of the motor, pump and jet will reduce your angle, while the weight of water and material, may or
may not balance that out . Like Sanman said, make sure you can adjust your sluice box in field .
Even the weight of the pump, and hose on one side will add horizontal angle, that is it may lean to one side .
The angle of input from your jet will also affect your flow greatly . Make sure your input from jet is slightly above your punch plate as well .
Good luck ..
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Re: 2" dredge build - sluice box design questions?

Postby kruzman » Wed Mar 25, 2015 2:45 pm

why would go put 3/4 in riffles in a 2in dredge especially on the east coast?
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Re: 2" dredge build - sluice box design questions?

Postby PAsniper » Wed Mar 25, 2015 3:40 pm

Thanks for the advice guys....

adawg, I've modeled everything for my dredge in AutoDesk Inventor, using physical properties for all materials (even water flow) and if my design and calculations are accurate, my center of gravity is right in the center of my floats.... Let's hope it is correct haha...

Kruzman, What do you recommend for riffle height? I was thinking of 3/4" clarkston riffles about 8 of them spaced roughly 2.375" apart, over miners moss. But the uppermost section of my sluice (14 or 15") would be 1/4 punch plate sitting 1/2" high over V-mat.

Any advice appreciated...
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Re: 2" dredge build - sluice box design questions?

Postby adawg » Wed Mar 25, 2015 4:24 pm

I don't see a prob with the 3/4 inch riffles, maybe wrong .
Are you using a jet flare, crash box or straight jet dump ?
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Re: 2" dredge build - sluice box design questions?

Postby Darin » Wed Mar 25, 2015 9:03 pm

I have not measured mine in a while but I am almost sure Keene 2" dredge riffles are 3/4" tall, and you need room between the punch plate and the top of the riffles, don't set it right on top of them. I can't remember but I think I have about 1/2" to 3/4" between them on mine.It's been almost three years since I built it.
You said the uppermost part of your sluice 14" or 15" would be 1/4" punch plate over v-mat.
I would rethink that I.M.H.O. , because that is the first half of you sluice. You want to catch your gold in the first third of your sluice. Put your best riffles there. Think of the rest of the sluice as a safety. I would stick with Hungarian riffles , expanded metal and carpet or moss.
That's just my opinion , hope it helps.
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Re: 2" dredge build - sluice box design questions?

Postby Sam Burgin » Thu Mar 26, 2015 7:59 am

Your pump as advertised will produce 52 gpm, which is just under 7 cubic feet per minute, so your target of 80% throttle would yield 5.6 cubic feet per minute, or 0.09 cubic feet per second. At a sluice size of 11x33, this water is going into a channel whose volume is 0.21 cubic feet per one inch of sluice height.

So, at 0” drop, you could expect close to (.09/.21) = .42 inches, or close to 3/8 inches of water in your sluice. The greater the drop, the thinner the water.

Riffles, carpet, matting, and material will raise the water level in your sluice, but not the amount of water in your sluice. If anything all that stuff will impede flow of material through the sluice, hopefully.

If you can’t adjust the drop and position on your sluice, you will never get it to operate to its full potential. BTW, nice idea on the floats.

Most everyone eventually migrates to pressure pumps for their dredges. The Keene 2” series of dredges have 100/gmp of water, which means a lot more flexibility to control your water in the sluice.

Lastly, if you are running two sluices, you will need to appropriately divide the water you have. I’m not sure 52 gmp is sufficient for a two stage. On the center of gravity, don’t forget to add the 15 pounds of water within your hoses hanging off the back of the dredge.

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Re: 2" dredge build - sluice box design questions?

Postby sanman » Thu Mar 26, 2015 9:01 am

Sam, you got a PM on the way....
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Re: 2" dredge build - sluice box design questions?

Postby Sam Burgin » Thu Mar 26, 2015 7:58 pm

Steve reminded me that I had not included the couple jet in my calculations.

I didn’t include those calculations because I didn’t feel a trash pump would present a significant amount of head pressure at the input. There may be increased water flow, but I’m unconvinced that 52 gpm will present a significant negative pressure at the nozzle.

The only way I could get my couple jet to work properly was with a high pressure pump. His results may be different.

Good eye Steve!!

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Re: 2" dredge build - sluice box design questions?

Postby PAsniper » Thu Mar 26, 2015 10:04 pm

Thanks for all the replies fellas!

Sam, that was exactly the answer I was looking for, regarding water height in my sluice.... So I'm assuming if my couple jet gives me enough pressure to up my flow, I'm hoping to bump my water depth to about 3/4".

I've had multiple emails back and forth with the inventor of the goldsnare electric dredge... Pretty impressive that he can drive a 2" electric with a bilge pump.... He was fairly confident in my design and was certain that my 52 gpm could get me excellent suction on my nozzle, as long as my head lift wasn't anymore than 3 foot or so.

Thanks for the compliment on my float... It's made of 2" XPS foam (closed cell) from lowes. With some sanding and wood putty to fix imperfections, then 7-8 coats of watered down PVA glue, I'll have a nice, hard, flexible base for paint. Very lightweight.

Have you guys had any experience with goldhog mats in a dredge? Doc from goldhog recommended to me to run alternating Talon / Scrubber mats, no punch plate, no riffles, no expanded. Just those mats. And he recommended having my sluice be adjustable from 3 - 8 degrees. Not sure if I'll go with that or not.

I hope to get more of the build done this weekend... And hope to post more pics. Once again, thanks to all for helping me out! That's one reason I love this hobby, it seems like everyone into prospecting are down-to-earth guys always willing to share knowledge and experience.

Take care guys.

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Re: 2" dredge build - sluice box design questions?

Postby shack » Thu Mar 26, 2015 11:01 pm

Rich,

Cool project! You've already gotten some great advice. Here's some more stuff to consider as you continue your build:

1. Riffle Height: Not sure about the Proline 2", but Keene's dredge riffles are 7/8" in height and the riffle set you use when you convert the dredge into a high banker uses riffles that are 1/2" in height.

2. Riffle Spacing: 2.375" is way to close together. Putting them that close drastically compacts the vortex in between the riffles and makes it practically useless for sorting, retention and discharge. Sanman and I experimented with riffle spacing by creating multiple sets of riffles with various spacing and angles. We tried 2.5", 3", and 4" riffle spacing and ran each set in a washplant sluice for a full day. The 2.5" riffles did not work well at all. 3" riffle spacing worked really good but required a steeper angle and more water. The 4" riffle spacing worked the best using normal angle and volume. Of note, the Keene 2" riffles are spaced 4" apart in both sets of riffles for their 2" dredge.

3. Pump: 52 GPM is not going to cut it, even at 80% of throttle. 3/8" of water depth through a sluice processing nearly 2" material will not allow it to function properly (retain & discharge). Most of the major dredge manufacturers use at least 90-100 GPM pumps. You're also using a wider sluice, so that's another factor to consider. Not sure about multiple stages on smaller dredges. If you go that route you will definitely need more water.

4. Sluice Width: With the pump you're using, you're definitely at a disadvantage with a wider sluice. If you stick with that pump you may want to consider an 8" or 9" wide sluice. Most 2" dredges use sluices that are 10x36. Lots of R&D has gone into dredge sluices over the past 4 decades, so try to start with what is proven to work and adjust from there if possible.

5. Crash Plate: 15" crash plate is fine. Gold will drop through the plate quickly with normal dredging so there's really no reason to have excessively long crash plates in there unless you plan on hogging material or running really fast. If you go with 1/4" plate try to get a plate that is at least 60% open and keep your crash plate height between 5/8 and 3/4". You may want to consider 3/8 plate and 40%-50% open with 1" crash plate height, that seems to work very well on the smaller dredges. I think you'll have to reconsider the pump because even 3/4" of water in that sluice won't be enough to clear above and below the crash plate. Also consider low-profile riffles under the plate directly after the top mat. They typically start about 8"-10" from the top.

6. Guts: Sluice guts are more of a personal preference and you'll see dozens of variations being used. Just keep in mind that you want the gold to drop, stop, and hide as soon as possible. A small section of black ribbed matting up top is good for spot checking and is fun to look at, but it doesn't provide a whole lot of protection for gold (of any size). It also scours easily if rock jams or buildups occur. Definitely do not line the entire top half of your sluice with only v-mat. You'd be wasting the most critical part of the sluice. Most of the dredge sluices you see only have like 6" or 8" of black mat. You want to introduce riffles as soon as possible as well as carpet, moss, and expanded. As mentioned above, adding a couple low-profile riffles right after the v-mat and under the crash plate work well too, just be cautious about clearance (material over riffles under the plate). Putting raised expanded over moss or carpet works extremely well if low profile riffles are not being used under the crash plate. In a nutshell, use whatever provides the most places for gold to burrow down and escape the flow.

7. Sluice Adjustment: Absolutely make your sluice angle adjustable! Besides changing the way you dredge and controlling material intake rates, being able to adjust the sluice angle is one of the primary adjustments you'll need to make and is a must have.

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Re: 2" dredge build - sluice box design questions?

Postby sanman » Fri Mar 27, 2015 7:36 am

•Are these the specs for your pump...?
•If so...the 49' head will give you 21.22 Psi., very low for a dredge...and that is WIDE open @ 4000 RPM's....as the pump gets some wear that Psi, will decrease...

•1.5" gasoline semi trash water pump
•Suction port diameter: 1.5"
•Discharge port diameter: 1.5"
•Discharge head: 25M (82FT) horizontals
• max lifts:49ft uphill
•Suction head: 4M (13FT)
•Maximum capacity: 12M/H (52 gal/min)
•Max power: 3HP at 4000 RPM
•Recoil starting system
•Motor type: air cooled, 4 stroke, single cylinder
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