adding power jet to gravity dredge

[spaghettigold]

hi all

In many places where i like to dredge there,s not enough drop to gravity dredge,Sometimes i can correct that by building dams but when there,s not enough natural drop on the spot to begin with,the dams must be build high ,which then creates a deep pool where i want to dredge .Since i ,m not allowed to use motors i can,t use compressors for diving,deep pools are a limiting factor.
I was thinking to build a maybe 2 feet high dam where i want to dredge to have a basic suction and then build a second higher dam somewhere else ,where i can get 6 feet drop to feed a power jet . Will this slightly increase my suction in the already with 2 feet drop working 8 inch suction hose to a good point? Should the hose that feeds the power jet have a certain diameter? Is bigger better?

 

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[rivets]

Six foot of head pressure equates to 1,8828 PSI which be 0.12609 BAR ( 10 meters = 1 BAR ) I would guestimate 3.5 BAR or 35 meters head or 50 PSI be a bare minimum to drive the size of dredge you are wrestling with and so you will need over a 100 feet of drop ...

Pipe size will determine GPM but this will have limited advantage in creating the venturi effect given the slight gradient simply because gravity's effect on water means its weight is dispersed in the pipe ... in other words you could easily hold the water back by sticking your finger in the orifice ... try this with your pressure pump and the answer to your question is self evident ...


Its funny because they sell these dredging pumps and call them high pressure pumps but in my little world i've water tested pipes with pumps up to 350 Bar which be over 5000 PSI



This has the makings of an excellent thread ... here's hoping the seasoned ( or marinated ) prospectors chime in

 

[spaghettigold]

thats also something i wanted to know ,how many feet of drop one needs to run a 8 inch power jet,thanks rivets.


I was hopingl 6 feet drop in to the power jet increase the suction to a ideal point if i,m almost there . In this vid you can see the waterflow with c.a 6 feet of drop,it was like a excavator at the suction inlet.


In the flat spots i want to work,I thought since the watercolumn in the suction hose is already powered by 2 feet of drop,maybe 6 feet drop in to the power jet could simulate /add the equivalent of 1 feet drop,so that it would be like i,m working with 3 feet drop which is near a good workable slope for my 26 feet hose.

thanks for the effort rivets

 

[Timberdoodle]

This is one of those questions where building a small 2" jet to test for improved suction would be worth some effort.
A basic understanding of how a jet works.
A jet works by entraining water in the fast outflow from the jet orifice which is travelling around 75-100fps (feet per second) depending on PSI. inside the jet once all the speed is transferred to the water column this causes certain pressure level which continually pushes water from the output of the jet. Water is drawn into the suction hose due to the low pressure area in this fast flow and replaces the water pushed out. (a jet's function is somewhat similar to how a centrifugal pump operates. A pump uses mechanical force to induce speed into the water which is converted back to pressure. A jet uses this pressure to induce speed through the orifice which then entrains the water and it is converted back to pressure)
So the key here is how much speed can be obtained from the pressure of a 6ft drop and will that be enough to induce additional speed into the suction line. I estimate around 25fps will be achievable which is slow by comparison and would then require a much greater orifice size to transfer enough energy through the jet and this is where trial and error comes in building a test jet.
In building a test jet I would start with a 2" jet with a full 1" orifice fed by a 1.5" feed line and give it a try to see if there is a improvement. Try different orifice sizes too see which is the best match.
If this works, I would simply increase all components 4x the initial size. 8"jet, 4" orifice, 6" feed line.
I think your idea has potential to achieve a very small increase in suction but that may be enough in those hard to work areas.

 

[rivets]

In this vid you can see the effect of the gradient at work ... the effect of gravity on the volume of water within the pipe in a vertical position compared to the other vid where the gradient was slight and so its weight dispersed throughout it and although head pressure remains the same over the 6' due to gravity the speed is increased by the same principle and so the increase of GPM thus more sucking power ........

And so this be a good example of the need for PSI and GPM working together ( speed of volume ) which Timberdoodle has explained ... it is possible to use water head/ PSI to increase itself and drive to a greater height ... a hydraulic ram pump being the example, but this delivers a tiny fraction of the volume required to drive it and so it will increase PSI but no GPM which a venturi requires both ....

 

[Hoser John]

I know dozens who tried and failed lotza luck as wimpy suction is no good,just use gravity suction and works just fine but jets not so much-John

 

[rivets]

Well I would heed what Hoser John says ... and so as the Jesuits have banned moto pumps and you will be syphoning for the foreseeable future your not going to need your jet which I would assume is were the plug up's mostly wedge, as well as the fact you wont be sucking up heavy/large boulders with your now limited suction power and so here is another

Plumber's Tip



Get rid of the restrictor on your hose as well as ream the inside edge of your pipe and this will significantly improve the flow rate

 

[spaghettigold]

This is one of those questions where building a small 2" jet to test for improved suction would be worth some effort.
A basic understanding of how a jet works.
A jet works by entraining water in the fast outflow from the jet orifice which is travelling around 75-100fps (feet per second) depending on PSI. inside the jet once all the speed is transferred to the water column this causes certain pressure level which continually pushes water from the output of the jet. Water is drawn into the suction hose due to the low pressure area in this fast flow and replaces the water pushed out. (a jet's function is somewhat similar to how a centrifugal pump operates. A pump uses mechanical force to induce speed into the water which is converted back to pressure. A jet uses this pressure to induce speed through the orifice which then entrains the water and it is converted back to pressure)
So the key here is how much speed can be obtained from the pressure of a 6ft drop and will that be enough to induce additional speed into the suction line. I estimate around 25fps will be achievable which is slow by comparison and would then require a much greater orifice size to transfer enough energy through the jet and this is where trial and error comes in building a test jet.
In building a test jet I would start with a 2" jet with a full 1" orifice fed by a 1.5" feed line and give it a try to see if there is a improvement. Try different orifice sizes too see which is the best match.
If this works, I would simply increase all components 4x the initial size. 8"jet, 4" orifice, 6" feed line.
I think your idea has potential to achieve a very small increase in suction but that may be enough in those hard to work areas.

thanks for the details timberdoodle.Unfortunately i,m in the process to add two 110mm (4.3 ") inlets to the flare.This will not increase suction but should at least solve the problem of rocks not clearing out of the box .Next i have to raise the mesh over the undersection some half inch,which i hope should help ,together with the increased waterflow to keep the under section from clogging with lights. Then i want to add 3 feet additional sluice run(unscreened expanded) that widens out from my actual 25 " to 35 inches for the case i have too much waterflow.
This is what i can do at the moment with time and cash available.
But i will come back to the power jet later.If you see a small potential that it could increase my suction a little bit thats all i need to know,because i have also places with 16 feet waterfalls.

What does the orifice look like?

 

[spaghettigold]

In this vid you can see the effect of the gradient at work ... the effect of gravity on the volume of water within the pipe in a vertical position compared to the other vid where the gradient was slight and so its weight dispersed throughout it and although head pressure remains the same over the 6' due to gravity the speed is increased by the same principle and so the increase of GPM thus more sucking power ........

And so this be a good example of the need for PSI and GPM working together ( speed of volume ) which Timberdoodle has explained ... it is possible to use water head/ PSI to increase itself and drive to a greater height ... a hydraulic ram pump being the example, but this delivers a tiny fraction of the volume required to drive it and so it will increase PSI but no GPM which a venturi requires both ....

Could,t it increase my suction a little bit...

 

[spaghettigold]

I know dozens who tried and failed lotza luck as wimpy suction is no good,just use gravity suction and works just fine but jets not so much-John

john,i would love to but then i need oxygen.

 

[spaghettigold]

Well I would heed what Hoser John says ... and so as the Jesuits have banned moto pumps and you will be syphoning for the foreseeable future your not going to need your jet which I would assume is were the plug up's mostly wedge, as well as the fact you wont be sucking up heavy/large boulders with your now limited suction power and so here is another

Plumber's Tip



Get rid of the restrictor on your hose as well as ream the inside edge of your pipe and this will significantly improve the flow rate

hi rivets ,i experienced how the restrictor ring and the bend of the nozzle took away power. Here,s my thread look at post #130 http://www.treasurenet.com/forums/gold-prospecting/433395-8-inch-gravity-sluicing-9.html What do you mean by ream the inside of the pipe?

 

[rivets]

Pipes when cut have a bur on the inside lip ... and especially in your case using syphonage restricts the inlet face of the pipe causing turbulence ( negative pressure ) right where you don't wont it ...

this may sound insignificant but in smaller syphonic pipes can effect flow rate by 50% + ...

understanding syphonage is the waters energy giving gravity the and so it pays to help in every way


File the inside lip nice and smooth at an angle ... in other words give that pipe some love

 

[Timberdoodle]

thanks for the details timberdoodle.Unfortunately i,m in the process to add two 110mm (4.3 ") inlets to the flare.This will not increase suction but should at least solve the problem of rocks not clearing out of the box .Next i have to raise the mesh over the undersection some half inch,which i hope should help ,together with the increased waterflow to keep the under section from clogging with lights. Then i want to add 3 feet additional sluice run(unscreened expanded) that widens out from my actual 25 " to 35 inches for the case i have too much waterflow.
This is what i can do at the moment with time and cash available.
But i will come back to the power jet later.If you see a small potential that it could increase my suction a little bit thats all i need to know,because i have also places with 16 feet waterfalls.

What does the orifice look like?

The orifice would be the point of maximum restriction in the powerjet pressure inlet side. In a Keene powerjet you will find a hourglass shaped restriction point. In a homemade jet the "orifice" is the welded on jet pipe which is smaller in size than the pressure hose feeding it. Will it work well enough is still a question in my mind. I have run jets with as little as 5-10psi and seen great improvement on suction. The ability of a flow of 25fps to help induce a flow speed of 12fps vs something like 6fps in the suction hose for good suction is a question that is best answered in a couple hours of building a small test jet at very minimal cost and time before ever trying to make a 8" jet. If it wasn't miserable weather I would be out building one now to try and better answer your question. Maybe next week I will have the time and weather co-operating. The biggest difference between this idea and using a standard jet that's gravity fed is the size of the orifice. A standard jet with a normal orifice for a pumps use is small (commonly 1/16th the jet area) but passes volumes of water under speed created by the pressure. In this test the use of very low pressure (2.6psi) with an orifice of 1/4 the size of the jet area will pass a similar volume of water. What I like about this approach is that to achieve good syphon suction in a gravity dredge usually means that you need 4-6ft of drop which may require 100ft or more of hose length in the area your working which corresponds to high costs of suction hose and dealing with jams etc.. If the gravity assist jet works you could run cheaper hose/pipe uphill to gain some of the suction required for good operation.

 

[spaghettigold]

Pipes when cut have a bur on the inside lip ... and especially in your case using syphonage restricts the inlet face of the pipe causing turbulence ( negative pressure ) right where you don't wont it ...

this may sound insignificant but in smaller syphonic pipes can effect flow rate by 50% + ...

understanding syphonage is the waters energy giving gravity the and so it pays to help in every way


File the inside lip nice and smooth at an angle ... in other words give that pipe some love

you mean the suction tip pipe?Because after the swivel tip there,s no pipe ,only hose.

 

[spaghettigold]

The orifice would be the point of maximum restriction in the powerjet pressure inlet side. In a Keene powerjet you will find a hourglass shaped restriction point. In a homemade jet the "orifice" is the welded on jet pipe which is smaller in size than the pressure hose feeding it. Will it work well enough is still a question in my mind. I have run jets with as little as 5-10psi and seen great improvement on suction. The ability of a flow of 25fps to help induce a flow speed of 12fps vs something like 6fps in the suction hose for good suction is a question that is best answered in a couple hours of building a small test jet at very minimal cost and time before ever trying to make a 8" jet. If it wasn't miserable weather I would be out building one now to try and better answer your question. Maybe next week I will have the time and weather co-operating. The biggest difference between this idea and using a standard jet that's gravity fed is the size of the orifice. A standard jet with a normal orifice for a pumps use is small (commonly 1/16th the jet area) but passes volumes of water under speed created by the pressure. In this test the use of very low pressure (2.6psi) with an orifice of 1/4 the size of the jet area will pass a similar volume of water. What I like about this approach is that to achieve good syphon suction in a gravity dredge usually means that you need 4-6ft of drop which may require 100ft or more of hose length in the area your working which corresponds to high costs of suction hose and dealing with jams etc.. If the gravity assist jet works you could run cheaper hose/pipe uphill to gain some of the suction required for good operation.

"I have run jets with as little as 5-10psi and seen great improvement on suction." You have seen this improovement in a gravity dredge assisted by power jet ?

"If the gravity assist jet works you could run cheaper hose/pipe uphill to gain some of the suction required for good operation." Thats exactly what i was hoping for.I can have 164 feet of pvc 4.3 " hose for about 100 dollars. Not sure about 6" but may be obtainable.
I have no workshop and all that must be welded and bended i have a metalman doing it,Thats why it,s costly for me.Besides getting it done correctly,my river is couple hours by car away so testing is always a big time and cash investment .It would be great if you can test this(no psi)

Another question;would multiple jets along the hose add up force?

 

[spaghettigold]

huh..and i discovered the like button

 

[Timberdoodle]

I have run submersibles on low pressure bilge pumps with good suction since there is no lift necessary above the water. I haven't run a gravity dredge assisted by a jet but I will try a test this next week and let you know how it works out.

 

[rivets]

The hose is the pipe

 

[rivets]

Spaghetti ... Timber ... I like your tenacity ... and you are correct if you can speed up the flow + add volume into the pipe/hose ... it results in more suck ... and I would position this low pressure jet much further up the pipe than you would a high pressure one


This reminds me of when I worked as a chemical cleaner/hot oil flusher/pipe tester on a oil rig and the right dodgy things I would come up with to counter act temperature ...


Think steam jet

 

[spaghettigold]

yes rivets,it,s seems obvious from what i,ve read that its difficult to run a power jet by gravity because it takes a huge amount of head but since i just want some assistance from the power jet maybe there,s some potential.It,s all about increasing opportunities,optimizing and then maybe have another 3 or 4 additional spots where i can work ,that where out of reach before.

Since where dreaming around a little bit here another question; Would the water in the 3 inch pipe rise over the level of the 8 inch hose intake?If so,how much c.a,again thinking the 8 inch hose has 6 feet of drop.
Emilio