New Zealand Gold Prospecting & Metal Detecting Forums Archive

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JW's Gravity Powered Dredge

Glennl		Posted : Saturday, 28 May 2011 3:40:58 AM(UTC)
Rank: Gold Dust Groups: Registered Joined: 3/03/2011(UTC) Posts: 6 Location: nelson, NZ Thanks: 2 times Was thanked: 2 time(s) in 1 post(s)		Hiya, I too have been interested in this system for a while. I have trialled the idea on a small pvc version with enough success to upscale it to a 2 inch power jet. The original idea was to save me lugging a pump onto site but now with it working I realise with the set up time and the weight involved it would be quicker to just carry a pump onto site! but not half as much fun, and its absolutely silent so even the birds still come down for a play..I will try to upload a couple of short movies I took, but they aren't great as I was worried I would drop my camera in the water, and that only left me one hand to use the sucking end but it gives a good enough image of it in action! But you get the idea. I have about 15m of drop over 100m which gives sufficient oomph to create about 20psi. I had 50m of 100mm pvc layflat hose into 50m of 50mm fire hose into a reduced stainless powerjet and a 50mm suction line. On the video I had a galv. tin shield made up to slow down the water flow, not realising how effective the system would work, so there is water (and probably my gold) going every where!), but for a first time effort I wasn't too worried. Since this was taken my 100mm line was fleeced by some light fingered sod who will get there's once karma catches up with them, but will get into it again once the days warm up, not that it feels much like winter yet. The detector will keep me warm for now. File Attachment(s): IMG_0024.JPG IMG_0025.JPG

mwyatt		Posted : Wednesday, 23 March 2016 4:22:49 PM(UTC)
Rank: Gold Flake Groups: Registered Joined: 14/12/2015(UTC) Posts: 28 Location: Auckland Thanks: 72 times Was thanked: 15 time(s) in 8 post(s)		I'm also looking into the Gravity Dredge idea. JW where did you say those pipes of yours is located? :) The lay flat hose won't work, since gravity dredging (siphoning) works on negative pressure. JW you mention first using 2" hose. Any feedback? Is your reason for opting to use 4" later on due to the amount of material you can move? Or did you have other issues with the 2" hose? In terms of DOC, this setup would still be considered to be hand tools right? :)

kiwikeith		Posted : Wednesday, 23 March 2016 9:13:20 PM(UTC)
Rank: Gold Ingot Medals: Groups: Registered Joined: 28/06/2011(UTC) Posts: 648 Location: hector Thanks: 359 times Was thanked: 230 time(s) in 154 post(s)		I think if you used layflat on the feeder then it would work . you would have to have a good head . I have been meaning to try it out , so I will get out there any other thoughts on the layflat

mwyatt		Posted : Tuesday, 29 March 2016 10:09:51 AM(UTC)
Rank: Gold Flake Groups: Registered Joined: 14/12/2015(UTC) Posts: 28 Location: Auckland Thanks: 72 times Was thanked: 15 time(s) in 8 post(s)		I did try out a 2" x 100' hose today in a local stream. With a 4' or greater drop there is some serious suction. You get your hand in front of the nozzle and it suck in your fingers or the glove gets suck'ed in. And it takes quite a bit of force to remove your hand again. I was also really impressed with how easily I could open up a 2' deep hole. The only issue I had was rock jams in my home made nozzle. Yeah, I was an el'cheapo and made a nozzle from a 2" mild steel exhaust pipe, learned a few lessons tho. Don't put the bolt to restrict the rocks being suck'ed into the hose half an inch deep in the nozzle (reason fingers got sucked in so often). Below is some of the pro's and con's I can think about: Pro's * good suction with +4' drop (any less drop and you waste your time) * quiet (no motor) * privacy :) Con's * carry heavy hose to stream * limited to areas where stream has good elevation changes * tricky to prime hose and get water flowing * once primed, you have to be careful not to suck air, else you start priming again Apart for that, I would say it was quite a successful test and it is a viable option in very specific applications.

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