revisiting the gravity dredge

[SierraMadre]

Hydrostatic pressure = .052 X weight of fluid in pounds per gallon X height of column of fluid in feet. Water weighs about 8.3 pounds per gallon

 

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[SierraMadre]

Water from 100' above would exert a pressure of 43 psi. Makes no difference if it's in a 6" hose or a 1" hose. 43 psi. Of course there would be a great difference in volume. Also you would not get more pressure by swageing down from a larger hose to a small one

 

[beekbuster]

do you need less pressure to run a suction nozzle?

 

[SunshineMiner]

princeipedeleon... I'm wondering If you have a section saaay... Flexihose header ---> Section of Hard PVC Pipe ---> Layflat --- > Section of hard PVC --> Sluice

Use it sort of as a connector in the middle? I wonder if that would work as technically your nozzle and the section of hard pvc are taking up the brunt of the suction force, supplying the layflat as it rolls downhill gaining velocity/keeping suction? BUUUUUT I see a huge problem with layflat in regards to ANY bends/little restrictions along the hose will cause material buildup and be an overall bad day. I like the idea though... *strokes chin*

 

[principedeleon]

You make pressure by reducing the hose size down. Thats how they used to use it for their hydraulic mine monitors... Imagen a 8-10" pipe reduced to 2" .. With a 20' waterfall and some reduction of hose in the bottom you could be supprised the power you could create.

The gravity suction could be so powerful that it would overcome any suction from ALL dredges. I wouldnt want to put my hand in front one of those rocks or how about unplugging a plug up.. It will destroy your hoses in no time.

 

[principedeleon]

princeipedeleon... I'm wondering If you have a section saaay... Flexihose header ---> Section of Hard PVC Pipe ---> Layflat --- > Section of hard PVC --> Sluice

Use it sort of as a connector in the middle? I wonder if that would work as technically your nozzle and the section of hard pvc are taking up the brunt of the suction force, supplying the layflat as it rolls downhill gaining velocity/keeping suction? BUUUUUT I see a huge problem with layflat in regards to ANY bends/little restrictions along the hose will cause material buildup and be an overall bad day. I like the idea though... *strokes chin*

My use of the lay flat hose would be mostly for supplying water. I wouldnt use it for running material threw it.

But it could be done by placing the layflat where the water gains most of the velocity since thats where you have less clog ups and straighting the hose the most you can without trying to restric the inside diameter.

I would for precaution would reduce the suction nozzle more then normally and feed it slower.

But unplugging a layflat hose is something i havent never went trough and would prefer PVC pipe Or straight regular suction hose.

 

[spaghettigold]

Here's a site I use for pressure conversions Online Conversion - Pressure Conversion
From their calculations 70' of drop (70 feet of head) will get 30psi so a power jet would be very difficult to use unless you have lots of hose and a tall waterfall above you nearby. A 20' drop will give 8.6 psi of suction at the upper end of the hose, making it doable using the standard 1 hose set up that dumps onto the sluice. However using gravity as a supply for a highbanker is doable, since pressure isn't the issue, only supply gph.
I'm curious about how the layflat, vacuum or pressure thing will work. Good idea for running a highbanker in non-motorized/non-mechanical areas

ok,70 feet of head gives you 30 psi. Now psi stands for "pounds per square inch". A 8 inch diameter hose cross section has c.a. 50 square inches,so we have 50 times 30 pounds of pressure.If we neck down to 1 inch isn,t it 1500 pounds in that square inch in a static (no waterflow)water column? And if we take the cap of and let the water flow,is all that pressure transformed in gph or does the pressure also rise a bit? Has there to be a certain angle when necking down ,like the 11 degree angle in the jetlogs ,so we don,t loose force

 

[SpecJet]

ok,70 feet of head gives you 30 psi. Now psi stands for "pounds per square inch". A 8 inch diameter hose cross section has c.a. 50 square inches,so we have 50 times 30 pounds of pressure.If we neck down to 1 inch isn,t it 1500 pounds in that square inch in a static (no waterflow)water column? And if we take the cap of and let the water flow,is all that pressure transformed in gph or does the pressure also rise a bit? Has there to be a certain angle when necking down ,like the 11 degree angle in the jetlogs ,so we don,t loose force

Doesn't work that way, the head pressure (psi) in the 1 inch pipe will be the same as the 8 inch pipe, you would just get a reduced flow in GPM. The total height difference between inlet and outlet determines pressure. In your example, the reducer from 8 to 1 inch would feel the load of PSI x square inches minus the area of the 1 inch outlet.

 

[spaghettigold]

Doesn't work that way, the head pressure (psi) in the 1 inch pipe will be the same as the 8 inch pipe, you would just get a reduced flow in GPM. The total height difference between inlet and outlet determines pressure. In your example, the reducer from 8 to 1 inch would feel the load of PSI x square inches minus the area of the 1 inch outlet.

30 psi x 1square inch minus 1 square inch =29 psi?

 

[spaghettigold]

Where does the whole waterweight from the 8 inch diameter watercolumn go,thats the part that i dont understand.Are you saying the weight of the water is pushing evenly in every direction,not downwards to the 1 inch outlet?

 

[MadMarshall]

A Gold Fever Experience - Gravity Dredge Plans - Olympic National Park

Maybe you find this link useful

 

[spaghettigold]

Thanks MadMarshall,i know the site ,best site for the standard gravity setup.
Since i,m dealing with a watershed that has spotty waterfalls but runs flat inbetween (like 10000 feet distance from 1 waterfall to the other) and good gold is after the waterfall where river widens out dramatically,i,m interessed if it,s possible to run a powerjet or maybe a infinity since it seems to be more effective,by using the VOLUME of the water to amplify the force given from the head of waterfall.The head of the waterfall alone seems not to produce enough amount of pressure in a setup having the same diameter all the way down to the jet.
I have a almost 20 feet waterfall that is 80 feet wide.So there is a big amount of energy ,tons of waterweight going down every second.How do i transfer this energie in to a ventury system.The energie is there.

 

[beekbuster]

yes... what he said^

 

[spaghettigold]

Hi beekbuster.
If i get some info ,i shure share it here.
Enyway this is brainstorming for the future,even if its possible, it wan,t happen this year,still got to build and refine the basics of my dredge.

I will keep my ears in radar modus

cheers;emilio

 

[beekbuster]

60 ft of 4 inch abs and 20 ft of 3 inch suction hose will work just fine for many creeks not too far from here. it seems that is the way to start. at some point ill tinker with it and see what happens. my hypothesis is that the weight of the water in the 4 inch cylinder will increase the suction ability of a three inch intake. ill see what happens. im sure anyone with basic physics or hydrology already knows this answer.

 

[spaghettigold]

hmm..i thought of it in the other way.The bigger hose as a intake only for water to run a powerjet.Are you talking about the standard gravity setup with gravel suction hose directly to sluicebox or about a powerjet setup?

 

[beekbuster]

the traditional gravity setup is what im going to make because its a sure fire method, my origonal post was trying to use gravity to power a venturi. sounds like a long shot given the tables in the link that was posted.

 

[spaghettigold]

Shure easyer with the traditional setup.
However,i don,t know if it will increase the power at suction intake if you have the smaller intakehose there.
To be able to suck out some crevices i took 4 feet of a half inch hose between my fingers and held my hand with the hose over the intake of the 4inch.
It did not increase the suction at the intake of the half inch hose,but it braked the flow in the 4 inch.
Test and let me know.
Happy hunting

 

[beekbuster]

i now have 1st hand experience with a gravity dredge. results are in... it does not take much slope at all to be successful. i acheived it with just 20 ft of hose. problem was the difficulty in seting up a sluice in the terrain i was in. the sluice ended up taking on a lot of water and i lost all the gold that was there. heart breaking. luckily i didnt have full confidence in the setup and i sniped all the big ones i could see, eventually i stopped sniping and just let the hose take it all. saw a few nice pieces in the sluice that were gone during clean up. but i did snipe my largest one yet. 11 grains

 

[beekbuster]