revisiting the gravity dredge

[principedeleon]

Nicee .. Good spot!! If you want to keep moving forward you could attach a piece of pvc pipe and add a extra piece of hose to give yourself a better reach without losing gravity.

 

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[NeoTokyo]

Congrats on getting it done and the nugget!

If you want, come by and pick up the rest of the 4" dredge hose that didn't split.

I would just wrap it with heavy duty waterproof duct tap to make it last a little longer.

The last thing that I need for my 5" setup is the nozzle.
There is a badass swivel nozzle at the Miners Cache that I am going to pick up to finish this project off.

 

[beekbuster]

Nicee .. Good spot!! If you want to keep moving forward you could attach a piece of pvc pipe and add a extra piece of hose to give yourself a better reach without losing gravity.

my thoughts exactly.

 

[beekbuster]

what i found interesting is there is almost no wear on the nugget i found. it was in a large crack formed from where quartz had eroded from the bedrock. later in the day i noticed the moss covered bedrock had a spot about the size of a dinner plate that was so saturated in rust i would swear there was an old piece of rusted metal in the rock. bringing a hammer and chizel next time. i think that nugget may have came right off the rock it was sitting under.

 

[spaghettigold]

View attachment 1166504

thats a piece i ,d like to find someday.

It works,some refinements on the sluice and you are all in .

 

[beekbuster]

right place at the right time i guess, it was the first piece of the day too. im very happy, it dwarfs all the other pickers ive found

 

[DizzyDigger]

Nice little nugget!

Never found anything close to that size, but...well, someday.

Cropped your pic a bit:

 

[Adventure_Time]

Well it seems either way a gravity dredge of appropriate size will be highly immobile except perhaps adding extensions and readjusting angles as your pay streaks dried up. I'd utilize 2 (or more) intake pipes that merge before the last section of pipe before hitting jet log. Add ball valve in pressure pipe so you can easily start and stop flow without hiking 50-200ft every time you want to clean out or adjust flow. Obviously you aren't easily buying or moving 16" pipes of anything anywhere fast, doesn't seem overly practical logistically. Couple, or four, 8" intake pipes should be able to provide sufficient PSI & GPM to run a 4" nozzle, maybe larger? That is a lot of water..

 

[ClaimStake]

soo, if i may add in here.

I've been Gravity dredging for about 6 years now and i'll say the setups, math and physics i've seen could use some help.

firstly, don't bother with the corex rolls or the pvc the. best and cheapest rout i'v found that works vary well. is to use the triple wall drain pipe 10ft $7-10.

Advanced Drainage Systems 4 in. x 10 ft. Triplewall Pipe Solid-4550010 - The Home Depot

than couple these together with 10ft , lengths of corex. no more than 30 ft please with less than 60ft of triple wall or about 4+ft drop. this is your flexible mining hose you'll be holding on to, "THIS IS NOT USED AS A SLUICE"

4 in. x 10 ft. Corrugated HDPE Drain Pipe Solid with Bell-End-4540010 - The Home Depot

you'll need this to put the corex together with the triple wall.

Eastman 4 in. x 4 in. Flexible Rubber Coupling with Clamps-86007 - The Home Depot

attach the rubber coupler to the corex don't over tighten.

when you find a good spot with some rapids or fall start laying your triple wall out from the top down "BELL ENDS FACING UP" or it will suck air and try to fall apart.
hold everything down with rocks, don't worry about sealing the joints just try to keep them under water if you can so if they do leak a little itll suck in water. usually they pull themselves sealed.
the more you use the pipes they will get harder to get apart (3" anyway they can give ya a fight 4s not so much).

once you have it layed out you'll want to build up a bit of a rock dam at the head of the pipe. have the pipe as low in the water as you can, and stack the rocks on top of it, leave the whole bell sticking out.

at this point the pipes should start running on their own. hold all the corex you want to use under the water, get the air out.

attach it to the triple wall bell. should be sucking like a sob.

this setup is self starting, self clearing, fully modular, cheap, easy, and fairly durable.

be nice to your piping and itll last a while, the corex will start to get little tiny holes from wear. but as long as you keep it under water it cant suck in air.

the triple wall is somewhat flexible. will kink with too much bend. set the end of the pipe chain in a normal 12" sluice, have some water running into the sluice from the stream/river too not just the pipe. this will help eliminate build ups in your sluice, and help even out the blasting force from the pipe. I hold the pipe down with a rock in the sluice.

I've been able to get a 30ft setup running with ~2ft of fall, and still have plenty of power to work with. double that and oh mama. look out power dredge.

the pipes will wear after a while I usually get new pipes every year. not too bad. probably a couple months worth of continuous use. you'll notice the difference between new and old pipes. old pipes loose syphon not as much git. you can also see how marked up the inside of the pipe gets.

they work well for a while though.

edit: also shake and tap on with fist to bounce and send down any caught material out of the corex ridges. be careful with detaching the couple too. gold may get trapped there.

 

[ClaimStake]

here's a couple pics

 

[beekbuster]

how difficult is it to clean out the corrugated line?

 

[ClaimStake]

pretty easy just shake and bang keep it in the water sucking doesn't take much. you'll hear the heavy that got caught in it move down, when it goes silent its cleared. usually takes about 15 sec. the more corex you're trying to use the more work it is.

just went to the rock piles today here in Oroville. not much luck in getting it going, the fall is spread out too much. even in the rapids. and the rocks where we went were too small. nothing to hold the pipe down with.

 

[Adventure_Time]

Slope seems to be the biggest factor more so than just length, even a 4" hose of a 40ft length has plenty of water weight to produce suction at the nozzle but you need enough slope to get to increase it's effective weight. The other thing to consider is the amount of reduction at the nozzle is going to contribute immensely to your suction power. Once you get it in the hose you are golden because you aren't pumping the material up, it only gets faster the further down the pipe it goes. Logistically a venturi suction nozzle is just not practical comparatively. Plus you can use this method to highbank just as easy while one person is dredging with the intake.


(Total Water Weight/Nozzle Volume Squared) * Slope(gradient as %) = Nozzle suction in PSI


Cheers.


(note: your nozzle reduction must be flared/funneled otherwise you might as well just run a pipe of the same diameter as the water will want to pull the pipe instead of the water through the nozzle)

 

[ClaimStake]

Slope seems to be the biggest factor more so than just length, even a 4" hose of a 40ft length has plenty of water weight to produce suction at the nozzle but you need enough slope to get to increase it's effective weight. The other thing to consider is the amount of reduction at the nozzle is going to contribute immensely to your suction power. Once you get it in the hose you are golden because you aren't pumping the material up, it only gets faster the further down the pipe it goes. Logistically a venturi suction nozzle is just not practical comparatively. Plus you can use this method to highbank just as easy while one person is dredging with the intake.


(Total Water Weight/Nozzle Volume Squared) * Slope(gradient as %) = Nozzle suction in PSI


Cheers.


(note: your nozzle reduction must be flared/funneled otherwise you might as well just run a pipe of the same diameter as the water will want to pull the pipe instead of the water through the nozzle)

^what he said.

I've been able to get away with 2+ ft of fall but anytime I've tried less like yesterday. it just wont get go'n. no mater how fast the current is moving.

30ft of pipe with 2ft of fall is the least I've been able to work with. and at that it only just works. well enough to get something done though.

 

[2cmorau]

I found the thin wall pipe would load up in the dips and curves, lost suction at the head, just bends to easy, (if ya can afford too buy the SCH 40 PVC)
so would have to pull the line apart and let all the material flush out into a tub, pain in the arse holding a tub in fast water
so i built this Sub surface, 4"ABS cut 1/4" slots and used an old wetsuit to line the sluice box
now i don't worry so much when the line backsup, just pull it apart, flush get back to sucking up that gold

 

[Hoser John]

Thin wall pipe is like thin wall dredge hose sold with dredges by some...just junk. Sealing junctions so NO air leaks that kills your suction is the chore as gravity suction stops easily. Lotza luck as water in EXTREMELY short supply this year-John