Gravity dredge variation.

[impfected]

I have been thinking of making a gravity dredge to use in a remote location to save weight and fuel.
I was thinking that instead of using the upstream end of the siphon hose as the suction side of the dredge, can I instead use it as the hose to develop pressure for a standard suction nozzle at the end of the siphon hose and have a standard hibank/floating dredge setup at the bottom where the work is being done. Essentially illuminating the engine in the system.
Has anyone done this? Maybe I don' t have a real grasp at the length of hose needed to develop the needed head to replace a dredge pump.
I was thinking in the 3" size range.

Thanks in advance.
Alan In Seattle.

[dickb]

For every 33' of head height above the outlet, you gain about 15 lbs of pressure. Thats why you see most city water tanks about 100' above the ground. Same would work for the dredge if your pump puts out about 45 lbs pressure, you need the top of the inlet to be about 100' above the dredge. I think most pumps work at less than 45 lbs.

Dickb

[Sean C]

This is something that I have also been wanting to do. I'm no engineer, but in my mind I figured if you start with a larger intake diameter hose and necked it down to a smaller hose before reaching the jet tube, you could create more pressure with less head height. Any thoughts?

[russau]

this is true to an extent! but you still need the height to attain the needed pressure. decreaseing the size of the opening at the venturi/venturis is where the pressure is amplified. you do need to keep your hose as big as you have all the way/or as close to it as you can get.the bigger hose allows you to maintain that needed pressure.

[Geo-George]

Pressure remains constant regardless of intake size. It's the "drop" or "head" that determines psi.
....and yes, you can make sufficiant suction to operate a nozzle.

A larger intake prevents cavitaion in the line due to the fact that, the falling water in the line can possibly draw in air in a vortex. The larger intake increases the surface area of draw, reducing the chance of a vortex and the vaccuum per sq inch of area. Say a 3" followed by a 1", a lot stronger draw at the 1" vs the same draw spread over 3". Use a screen of some type to keep pine cones or other debris out.
At the bottom of the line, where you are going to use the power, you will have a steady source to access in many ways. What can't you run off of a water wheel?

[Geo-George]

Here is some info from when I was reseachig the same subject.

"O.K., here's what I managed to find per your advice on finding a conversion table.

http://www.shipcopumps.com/mathwizard/m ... t-head.asp

It shows that 40' of head produces 17.3 psi
Now if I were to increase the head to say 60', the psi increases to 26.
The table also allows you to enter a psi and shows the required head.

A formula I found:
http://www.accontrols.com/documents/Wat ... etHead.pdf
Multiply the psi by 2.309 to get the feet of water, or......
divide the feet of water by 2.309 to get the psi. ( @ 62* F. )

I do thank you, finegold. You got me to thinkin' and pointed me in an great direction."

[ROKONRANDY1]

not a practical idea for dredgeing, works good for ground slucing or a shelf shotter, any time you can string some pipe of any size and store water to run threw it you will release the stored energy in the water. With a 12 inch pipe line you can store 3 feet of water over the pipe and when it is released into a bank it has the power to move a 6 inch rock. rokonrandy

[Sean C]

Pressure remains constant regardless of intake size. It's the "drop" or "head" that determines psi.
....and yes, you can make sufficiant suction to operate a nozzle.

A larger intake prevents cavitaion in the line due to the fact that, the falling water in the line can possibly draw in air in a vortex. The larger intake increases the surface area of draw, reducing the chance of a vortex and the vaccuum per sq inch of area. Say a 3" followed by a 1", a lot stronger draw at the 1" vs the same draw spread over 3". Use a screen of some type to keep pine cones or other debris out.
At the bottom of the line, where you are going to use the power, you will have a steady source to access in many ways. What can't you run off of a water wheel?

Are you sure this is right? A larger volume of water would weigh more thus increasing the its kinetic energy I would think. Wouldn't a 4" hose provide more pressure than a 2" hose given they both had 50 ft of drop?

[Hoser John]

Lots of work to set up and your water collection funnel system size,configuration and placement in a pond to supply the water is a HUGE part of the equation. All conical hose size restrictions up the psi and pumping stats do not apply to gravity feed as many other factors are then applicable. Works ok and definately the way to blackop or work extreme areas. Just caught some CENSORED on my buds claim and they cleaned out over a hundred feet a bedrock with a simple hose/solid pipes stashed in the bushes and a multi tiered terrain-tons a au 2 u 2 -John

[Geo-George]

Pressure remains constant regardless of intake size. It's the "drop" or "head" that determines psi.
....and yes, you can make sufficiant suction to operate a nozzle.
quote]

Are you sure this is right? A larger volume of water would weigh more thus increasing the its kinetic energy I would think. Wouldn't a 4" hose provide more pressure than a 2" hose given they both had 50 ft of drop?

Take one sq inch, now 1 sq ft. The overall wt. is more for the sq ft, but it's still the same per sq inch.
Now if you take the 144 sq inches from the sq ft and stack them, you have increased the "PSI" by 144.
Take that sq ft and stack 144 more on top, you have increased the "PSI" by 144.
In both cases the PSI is the same. Something to remember, "Gravity" pulls straight down.
By using a larger pipe you are only increasing surface area, not pressure.

Another name for the system you are talkin' about is a "Simple Simon" dredge.
If you have enough drop available, this is a very effective system.

You are right where I was, but I got my answers right here.
Again, I thank members for the solutions to my quandries.

If you go here, you'll find the sumation of my inquiries on the subject.
viewtopic.php?f=5&t=428&hilit=gravity+sluice&start=10