JW's GRAVITY DREDGE

[overtheedge]

I get the idea that this old technology has spurred a lot of think and so far the only person with know is JW. Early on, I got caught in a think trap that was wrong (psi v velocity). I admit that I don't know. The lay-flat collapsing has crossed my mind more than once. I tend to think that with friction loss being cumulative, it might work. It might need a restrictor near the lower end of the lay-flat and/or it might partially collase, but still provide flow, I just don't know. What I do know is that "the surest way to fail is to not try."

I have a 50' section of lay-flat coming from AMDS. I'll cut off the ends and try the install after break-up in a place I can easily and quickly set it up to try. If it works, good. If not, I'll use the lay-flat with my highbanker. I still have 150' of 2" PVC on hand to go with JW's type install.

In a way, this discussion sort of reminds me of the Clarkson sluice study. A whole lotta miners thought and did. Clarkson found out that the miner's think was erroneous. Without an actual attempt being made to see if this idea will work, no real knowledge is added, but rather speculation.

I mean no disrespect to anyone and value everyone's input. We are so used to using pumps that we forget some of the fundamentals. A 100GPM 50psi pump will produce 100GPM at almost 0 psi. It will produce 50psi at zero flow. If we restrict the flow, the pump can compensate to stay on the performance curve. In gravity based systems, the head is constant. The GPMs are restricted by head, cross-section of the pipe/hose and friction loss. The higher the flow rate, the greater the friction loss.

We interrupt this program to allow everyone to just smile, shake your head and chuckle at my foolishness.

Today I start the build of the sluice and header assembly. Actual testing is gonna have to wait about a month and a half. This will still give me a couple of weeks to iron out any wrinkles before the higher elevations go through break-up.

I have Dan's wide and narrow sluices on hand, the highway cones and everything else ready. The hose from AMDS should be here in a couple days.

The flow might be too low for the wide box, so I'll make an alternate header that allows the sluice to be configured as a river-robber at the same time to get an adequate water column depth in the sluice. A better approach might be a moveable baffle on the upstream end of the box. Open and close it as needed to get enough make-up water. I prefer the wide box over the narrow box based upon capacity between clean-ups.

Dick, I noticed the same thing using lay-flat for irrigation. Less than a certaion amount of pressure, the lay-flat was pretty flat yet there was still some flow. With 1/4" screening or smaller over the nozzle (maybe 3/16" openning), I won't have near the problem with blockages if the hose doesn't completely expand. Only by trying will the answer be known. I can still run pipe, so the only thing I lose is a bit of time prior to break-up.

[AceHand]

OTE,
I absolutely agree there's only one way to prove if it works. There hasn't even been a lab test yet, only theory. This is uncharted water we're in. That's a good idea trying it in a more accessable area first. The first time I use any new stuff, I want to change or add something on it before I go out the next time.
Tom

[chickenminer]

Eric,
It will be interesting to see if it is possible to sustain a gravity flow with a slurry in lay-flat. Gotta agree with you guys, ain't nothing like trying ! Screening to - 3/16" or better ought to help a lot.

[overtheedge]

Dick, there are two reasons I'll have a small screen over the nozzle. First, the gold in the Copper River Basin usually is smaller than 1 mm and flat, like seriously flat, maybe 20:1 diameter to thickness. Then there is the matter of such low gradient. The larger the material you wanna send down the pipe, the greater the gradient needs to be to get the velocity to move it. I figure 1/4" might be close to max for gradients less than 1:10.

JW probably has the experience with siphon dredges and might know the material size to gradient figures.

Worked on the siphon dredge today and doped out a way to get any additional water I might need for the wide sluice. After making the roughly 2" x 9" oval hole for the highway cone flare, I just cut a couple holes, one on each side of the flare, to stick 2" pipe in. Figured that since I was handling pipe, I might as well use some for adding any additional water the sluice might need. The flare openning is about 5X the cross-section of the pipe and rather than sloping up to the box, will enter straight on. I want the water to be slowing down before it hits the sluice. Tempted to glue a short section of v-rib at the head of the sluice; might be easier to see whats happening.

[chickenminer]

JW probably has the experience with siphon dredges and might know the material size to gradient figures.

Well, here is my thinking. You are on your own .

JW's is not comparable with what you are trying to do with lay-flat. Totally different characteristics between flat and solid wall pipe/hose. You are bucking lay-flat's inherent tendency to do just that.....
lay flat! This is going to cause considerable more friction, or so it seems to me.

Have you given thought to how many feet of solid wall pipe you are going to start off with on the suction end? I would think the more the better in order to keep a sustainable gravity flow.

I'll be waiting for the "film at 11:00". Kinda wish I was there to help ya fiddle with it

[overtheedge]

Pretty well finished the dredge today. Just a hose clamp and duct tape. I'm not to spend a lot of money on this. Only spent money for 50' of lay-flat and some 1/4" machine screws. The rest was on hand.

With the low stream gradient and long runs to get the velocity, I figure to use 20-30 ft of pipe before trying the lay-flat. It may not work, but I'll cut all but a foot of two off and add more pipe. I'll leave the foot or so in line and use a clamp as the water gate for stating the siphon by filling the system. JW I think said something about plugging the bottom end with a tennis ball. I added a flare on the sluice so hard to plug and fill at the same time.

It'll be interesting, but still weeks away from break-up, too many.

[overtheedge]

Well, gonna see what happens. Mailed off the 2" siphon dredge application today to the FBKS office. I added an attachment describing the dredging system and all the info I could put together. I emphasized that the water velocity was limitted to the same gradient as the stream and therefore couldn't transport any material that the stream wasn't already capable of moving.

I went ahead and requested an extended season 15Apr-15Oct. Figured that they would either permit it or they would shorten it in the box they fill out. Anyway, we'll see.

[chickenminer]

Eric,
Have you had a chance to try out the new project yet. Curious if it worked at all for you and if so how well.

[overtheedge]

Permit date starts on 15 May. Probably just as well. Was a lot of shelf ice on the river a few days ago and over a 1/2 mile stretch, I was only able to get in the river in two places.

Did find something interesting though. One place was just below an inside curve of the river and among a fair size boulder patch, yet still pretty well along the side of the gut of the river. Figured there oughta be some good colors. Surprise, surprise. Very little colors compared to the top inside edge of the skim bars.

Appears that the < 1 millimeter flaky gold common to this area lacks the mass to settle out in the current of the gut. Water depth was less than a foot to foot and a half where I sampled. I was able to deflect the current where I sampled and even wrestled several 100-300 lb boulders out of the way. Wasted half a day, but learned a bunch about fine gold deposition.

Education doesn't come cheap. You can pay with dollars or labor. At the end of the day, how much goes in the poke?

Side note: At the upstream location where I was able to get off the shelf ice and into the river, there was a skim bar high and dry and most of all thawed out. I tried out my idea of digging with a garden spading fork. The four heavy tines worked well to get between the shingled cobble and pitch them aside. All that was left to dig with a shovel and classify out was the -1 5/8" material. The skim bar was at the high water mark. The garden fork will be be part of my kit from now on.