JW's GRAVITY DREDGE

[overtheedge]

Been rethinking the hose issue and something jumped out at me. First a caveat. My experience with hose is confined to forest fire fighting and irrigation. We used hose to the irrigation guns in the brome fields.

The size of the material and its ability to be moved by the stream flow is completely dependant upon gradient.

From USGS IC 6787 Placer Mining in the Western United States:
Material FPS
fine sand 0.5
coarse sand 1.0
Fine gravel 1.5
1" gravel 2.5

When hose is layed out and filled with water, it conforms to the supporting surface. It also has a way of wiggling around. Another problem is the inner surface is rougher than plastic pipe, but not grossly so.

Therefore it would seem that if we layed the hose, filled it with water and then walked the line and straightened out the kinks, its ability to move material might just work. It is all about the gradient and minimizing the kinks.

So from the crude table above, if we screened the intake to restrict the size of the material to what the flow will always push down the hose, we might be able to substitute hose for a substantial portion of the run. In my case, <1/8'-1/4" in a 2" hose might just work for a siphon dredge.

I can't see any reason why 4" hose wouldn't work for just water in gravity based supply lines. 100' sections of 4" hose are easily transportable and cheap compared to pipe. An added advantage might be the ability to use a hose clamp at the midpoint of the run and not have to go all the way back to the sluice to open the water line.

For low gradients (<4 degrees) I use a rule of thumb of 4"/second/degree of slope= feet per second of water flow. From what I can tell, the rule is fairly close to reality, but fails more and more as the slope is increased.

Am I sure of this? Nope, but it makes enough sense to me to buy some 2" lay-flat to try it. Worst case scenario; I have some 2" for the highbanker and don't have to reduce the 2" pump outlet to the 1.5" hose I currently have. The design I'll try is flex-hose at the nozzle end (screened to 1/8"), then 2" pipe for 10-20' (something to tie a rope to and use rocks to hold in place) then a hose run to the 10-20' of pipe at the sluice. For couplings, I'll use my old standby, exhaust pipe and hose clamps. From measuring, I found the threaded couplings and cam-lock fittings for 2" hose to be about 1.625" inner diameter. No sense in restricting the flow any more than I have to, hence the exhaust pipe.

Steve, I haven't found hose on the AMDS website. Do you carry it in stock or is it special order?

I should have stated hose without any fittings and in longer lengths. That is why I had the inner dimensions of the fittings in the previous paragraph.

[Steve Herschbach]

Hi ote,

Yeah we stock hose but are low until the Keene order arrives. What size you need? I do not list it on the internets as it usually is too bulky to ship but I guess I could list it as a reference item so people would know. WE do list layflat at http://www.akmining.com/cart/hose_co...d_fittings.htm

[AceHand]

OTE, uh oh, I really hate to bring this up, but I beg to differ. If you're talking gravity dredge and lay flat hose, it will probably work, but not as well as pipe. I don't think lay flat will work with a siphon dredge. Reason being that the siphon is sustained by the rigid walls of the pipe as the fluid below it creates suction to get the water out of the upper pond. Will this suction just suck in the walls of the lay flat hose instead of drawing more water in? The suction needs to be transferred all the way to the top to bring in fluid. If there is enough pipe above the lay flat, it may suffice but not be beneficial.
On the other hand, if you're talking jet style, the restriction at the bottom will possibly keep the lay flat expanded, but you still need sufficiant pipe above the lay flat to get it started. A lot of variables here and I don't know for sure what I'm talking about, but this is what I've deducted from the past few days. I sure hope I'm wrong because lay flat is cheap and easiest to transport but I have my doubts as to it's effectiveness. My wife says I sound like a jerk, but I hate to see anyone go to all the work of trying lay flat and finding this out. When we talked about hose before, I assumed it would be rigid.
Tom

[Jeff in ME]

While I know little about dredges I'm trying my best to follow along with this thread, as I have little knowledge about dredges compared to others on this site. This is an interesting topic.

When talking about power jets in the posts above, I'm guessing this supply line is separate from the hose and nozzle being used to suck up material. Although it would require more material be used, what's the possibility of using a double power jet (as used in twin engine/pump dredges) to increase the suction? Would this help (or even work) or would the suction be the same?

I understand it would require more material be hauled to the site, but as mentioned above, it's being hauled in once as apposed to hauling fuel every day.

Jeff

[AceHand]

OTE mentioned the double jet in post #39. Steve and him talked about larger orifices. They all sound like good ideas to me. A field test may be in order if anyone ever tries this with a questionable amount of head and has the parts to do so.
I've been trying to think of a small scale test for lay flat. I don't know of any small (1/2" or 3/4") hose that would work. I have 1 1/4" but a hill, water to location, fittings, etc. will take too much time when there's other priorities at work and at home. I don't think the roof will support a full horse tank of water, either.
I'm going to ammend my last post. I called a siphon dredge a suction dredge. Sorry for the mistake.
I don't believe I ever thanked JW for starting this post and sharing his pictures here. That's really some set-up you've got there. Draining the ponds to dredge and such, you've really put a lot of work into your project. Thanks to Steve and OTE also for the ideas and info. This thread has gone a looong ways for expanding JW's operation to other areas using alternate but similar methods.
I looked back in the thread tonight. I wondered for quite a while why the hydraulicers started their pipe large and got smaller. JW's right about cost and transportion but when he posted the friction losses from larger pipe you can see. That 4" pipe has hardly any friction loss. They weren't gaining pressure as I had originally thought, but couldn't figure out how, they weren't increasing velocity, they were just keeping as much psi and velocity as they could. Losing as little as possible to friction on the way down. JW stated that in fewer words, but it didn't register then. Maybe you guys knew that, but it just dawned on me today.
Anyway, thanks to all that have contributed to this. Now if only I could try it, lol.
Tom

[Vance in AK]

JW, if you were to dissappear you would surely be missed.
I have learned a ton & got a pile of great ideas from your posts already, & have LOVED learning about NZ.
Hang around. Besides, I want to hear how your trip a few days ago went.

[overtheedge]

Never thought I would get this excited about JW's siphon dredge.

Anyway found some info in the USGS Bulletin 263 "Methods and Costs of Gravel and Placer Mining in Alaska". On page 134 in the bulletin, there is mention of miners using canvas hose 6-14" in diameter to move water from the head ditch to the sluice. He called it flume hose and no more than 100" of water (?) and no more than 50' of head. I'm not sure what the author meant by 100' of water, but he did say he didn't recommend using it due to being makeshift, but allowed as it had use in primitive situations in remote areas.

It wouldn't be that difficult to add a restrictor at the bottom end if the hose is coupled to a length of pipe. Just get a PVC cap and cut most off the end. Hold it on with a sheet metal screw. An easier way to restrict the flow would be to compress the hose to 1" somewhere near the lower end. By compressing the hose, the cross-section drops from 6.28 sq.in. to 4.83 sq.in. I think for it to possibly work, the nozzle would have to be screened. Otherwise the restriction might become a dam and if you have to repeatedly walk back to clear it, you'll call it even worse.

If no one can show that this is violating some physical law, I'm gonna try it. JW's siphon dredge just opens up a whole new ballgame in remote areas and if lay-flat can be used for part of the install, its just that much less to pack in. I'm looking at 8 miles cross-country on foot. Now you know why I don't wanna hump the pump.

Gonna pick up 100' of 2" lay-flat anyway. Got threaded fittings on hand so if it doesn't work for the siphon dredge, I can still use it on my 2" pump.

[JDC]

I believe Ace is correct, the lay flat should work fine if you start off with ridged and then change over. With lay flat you will need to know the head pressure and make sure to be inside the tolerances of the hose your using. Also make sure to put a valve of some kind in the top of the system, I will bet if you have 100 feet of head your going to break something eventually and need to shut it down.

Jeff

[overtheedge]

2" layflat has a max presure of 80psi.

I'll be using it under low head conditions similar to JW's install. By low head, I mean 5-20 feet. Hence my need to really watch the friction loss problem.

In the south end of the Copper River Basin, the paystreaks are small; under 100cy and usually under 25cy. It takes an inordinate time to locate them and with the small size, a person has to watch the initial and operating expenses closely. Then coupling this with the lack of easy access, it adds in the weight factor.

As an example: If your pump consumes 0.5 gallons an hour, you run 10 hours a day for 3 days, you have to pack in 15 gallons minimum, about 100 lbs. Roughly 3 round trips each taking the better part of a day. Now just how much does that pump weigh? For a couple of locations, I can use a cart for most of the distance, but there are several spots where it is on your back getting past the bad area. Even carts are limitted in weight capacity on unimproved trails: couple hundred lbs maximum usable. I figured transporting 4-5 days in and another 3-4 days out.

I don't mind humping in with a day pack and a pan to locate the hot-spots, but spending days packing in (and out) a quarter ton of gear and supplies several miles for a few days operation doesn't make sense when the possible recovery is a few ounces max. Hence my enthusiasm for JW's installation and its capabilities. I should be able to get everything packed in in a long day; about 16 hours and 2 trips at my sustainable 2 MPH.

It IS all about economy. Time and money invested per ounce recovery. I will test the basic install for feasibility somewhere I can drive to. I already know JW's install works with plastic pipe, so the question is "paper or plastic" er .. no, it's lay-flat usage.

Thanks JW

[chickenminer]

Eric,
Hmmm... I think you are going to be very disappointed in trying to use lay-flat hose for that purpose. I have always used it in a pressure system and unless it was significant pressure the hose tends to compress on itself. In a strickly gravity feed situation I think you are going to end up with the hose wanting to collapse on your material it is suppose to be carrying. If the "flume hose" is like the old stuff I have seen here in the Fortymile, it is a stiff canvas. Nothing like todays lay-flat.