gravity dredge

Replies

Steel Pan May 18, 2010 at 7:11pm

No gas or oil, expences are expences. I'm a cheap old man. LOL
I put together a gravity fed "Long Tom". It will easily convert to a gravity dredge when Kalif. drops the ban.

Here's some great info on gravity dredging that I gleaned from another site.

http://goldfever.com/g_dredge.htm
- andrew hall > Steel Pan May 21, 2010 at 9:03pm
  
  when pumping water uphill, the issue is head loss,when running water by gravity downhill,for a suction device,lets call it head gain.power jets require less volume than a suction nozzle,but are usually unusable in a gravity dredge scenario.if hookah air is unnecessary,then the deposit would be shallow.thus,a suction nozzle is necessary.as these require higher volume/pressure,a viable suction dredge system requires lots of head gain/volume.if the nozzle has a 1.5 hose inlet,like a 3 or 4 inch dredge has,then i would start with about a 4 inch intake at the water source.topography dictates the length of the water supply line.as viable deposits typically occur at a certain drop per mile of streambed,a good gravity line can be many hundreds of feet in length.sometimes a water source is available closer/higher as with a nearby tributary with a steeper gradient than the targeted watercourse.as economically viable deposits are rare,then rarer still are such places where a g-dredge could work without a long water supply line.am not trying to pee in anybodys wheatys,its just physics.i have been working on this idea for a while,even in my sleep.had a sweet gravity highbanker setup earlier this winter,was using 400 feet of 2inch poly plus 100 feet of 1.5 fireline.just to run a almost stock keene combo unit in highbanker mode.worked best at night,when flow volumes were highest.would clean the intake strainer on the way in,walk the 500 feet of line down to the digsite,turn a quarter turn valve,and start feeding the hopper.was the most fun ever had highbanking,no pump noise.very cold and wet though.and gravity water sources can carry a lot of intake clogging materials(leaves etc.)as an intake dam is probably required,a proper spillway must be in place,to let these materials pass over the dam.even so,the intake suction involved will still draw these to the intake screen.physics.if you must run 500 feet uphill,fighting briars in the dark several times per night shift,and do pick and shovel work the rest of the time,while soaking wet at about 35 degrees,your day job might suffer.gravity dredging/highbanking has taught me more than any other type of mining,especially about hydraulics.there is an entire science involved.water can be complicated.but well worth learning.the knowledge gained is as good as gold.best wishes.
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  - Steel Pan > andrew hall May 22, 2010 at 10:09am
    
    To deal with the debris clogging my system, I use some widow screen to stop any material entering my water collection funnel. The screen will be placed aprox. 2 ft. upstream from my funnel. It will be set so that water can flow under the screen, should the upper surface area get clogged, which will only be about 3" under the surface of the water. This design saves on having to walk upstream to clear out the funnel.
    Another thing about my design is that, unlike commercial units that have smaller tubing with even smaller holes for making a spray into the header box, the flow from the 1 1/2 " line is disperced across the width of my home made grizzly using a baffle. Any possible clogs can be cleared from inside the grizzly by just removing the internal screens for cleaning.
    I figure to have a maximun flow of aprox. 63 gpm flow into my grizzly/sluice.
    - andrew hall > Steel Pan May 23, 2010 at 3:54pm
      
      that is one good way,is how i run my home irrigation intake from my spring water supply.spray bar setups in a hopper should not have end caps glued on,as unclogging debris would be nearly impossible.a quarter turn valve just before the spray bar is mandatory when using long supply lines.but, you can kill two birds w/one stone if you run a long flume from dig site to hopper head.like a Z,the top horizontal line is the flume,diagonal is the hopper/grizzly,bottom line is the sluice.if you already have a power sluice header diffuser,great.put that at top of flume.or build one and save $.flume needs some slope,depending on material being run.this allows clay and hardpack stuff to completely dissolve before reaching the grizzly.which can now be steep enough to properly self clean.even better is that you can throw the strainer in the truck and never again shut down to fuss with clogged up screen.just figured this out recently,my per shift yardage capacity more than tripled,with 1/6 of the effort spent.the suction created at the intake of a 500 foot 2inch diameter gravity line is truly amazing.one night while still using spray bars,biggest clog up ever.turned the valve off,popped the end caps,turned the valve on.a piece of 10 mil visqueen about 12 foot by 6 foot was ballistically ejected into the dig hole.in one long black blur.had been sucked right out the dam works,by all the suction power created by the head gain.and passed thru splices reducers,elbows valves,tees,etc.any old plywood will do for the flume,longer the better.10 inch width is great starting point,as commercially made power sluice headers drop right in.and would be a modular part of your equipment,as carpets,screens,hoppers etc,are 10 or 12 inches wide.one could be added at downstream end of a standard keene a52 sluice for instance.or the a52 sans carpet and riffles installed at upstream end of flume,for errr other purposes.used that setup once to flush about 300 yards of stockpiled tunnel debris through a recovery system based upon a large highbanker.in the Z configuration,but with about 30 feet flume.sat in a chair and directed the water flow,while processing the previous cleanup.hard to find sites like that.good luck,and have fun.
Gold Seeker May 18, 2010 at 7:07pm

Ray,

I would say that if all they are saying is "No Motors" you should be fine, if they say "No Dredges" then there maybe an issue.

I know that in N.C. in the Uwharrie National Forest, they say "No Motorized Equipment", and they also say "No Dredging" and they will not even let you use a "hand held suction tube A.K.A crevice sucker" the kind made out of PVC pipe, they say that it is considered a dredge because it sucks up sand and gravel, I know this sound crazy but that is what the Rangers Station is saying to anyone using one or asking about using one.

On the gravity dredge the bigger the pipe the better, I would use a 10 ft. piece of 4" PVC pipe and then go to 3" then go to 2" and attaching your hose to the 2" PVC, you can cut the 10ft. pieces in half and use couplings to connect everything together so it will fit into your car, don't use any glue when connecting the pipe.

You will have less friction loss with the pipe, also the pipe will be in a straight line, any bends will be a loss in water flow/pressure.

Good luck and let us know how it works for you!

Skip
- Douglas Sayre > Gold Seeker May 19, 2010 at 3:22pm
  
  The problem with a gravity dredge is getting sufficient head to create a good vacuming action. You need about 6 to 10 feet of fall per hundred feet of pipe to get sufficient sunction and minimize jams.