moving sand

[pvet7521]

I would like to know all and any way to move sand in 130 ft of water . And it has to be done inconspicuously. I need to move about 3 ft of overburden covering a complete ballast pile. All credible suggestions appreciated.

 

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[Salvor6]

The best way is with an air lift dredge for several reasons. First of all it is easy to build, cheap, and it works great at 130 feet. Here is a pic of a 4" dredge I built out of PVC pipe.

 

[Jason in Enid]

Like Salvor6 said, an airlift will be your best option for work at 130 foot deep. The longer your expansion/dredge tube is, the more force your air will generate. Just be careful because it can create HUGE amounts of suction if you get carried away. Your biggest problem will be working time at that depth.

 

[Dell Winders]

The problem is an air lift requires a large volume of air from a big noisy compressor on deck. A great attention getter. Dell

 

[Jason in Enid]

The problem is an air lift requires a large volume of air from a big noisy compressor on deck. A great attention getter. Dell

Lots of SCUBA boats carry onboard compressors. Don't see why it would be an attention getter.

 

[FISHEYE]

For deep water dredging instead of using air you use water.It works the same way and is a lot better since with pumping water you have gravity helping you.

 

[Jason in Enid]

For deep water dredging instead of using air you use water.It works the same way and is a lot better since with pumping water you have gravity helping you.

What? How is gravity helping? When using a water pump, from the deck to the surface you have a few pounds of gravity pressure, but that is nothing compared to 80-100 psi generated by the pump. There is no added gain below the water surface. Air lift, the suction can be changed by extending or shortening the up-draft tube. Due to the costs and difficulty in moving pressure hose underwater, the clear advantage is to the airlift.

 

[AUVnav]

Fisheye has the right idea...basically a subsurface dredge...dont use compressed air, just use water pressure.

The surface vessel can provide the water pump, which goes down to a section of pipe, suspended horizontally near the bottom. The jet type of suction works the best, not a suction nozzle...

This moves the overburden to the end of the suspended section of pipe...

(perhaps by gravity he means the water going down from the surface to the dredge.)

Bottom mover on steroids

 

[FISHEYE]

All deep water dredges and trenchers use water jets and water jet pumped suction devices to remove over burden.Pumping high pressure air down deep would take a compressor the size of a house.Any other pump just wouldn't cut it deeper than 30 foot.Its all about physics.Get a 10 foot aquarium tube and put a weight on it.Then drop it in a pond or tank that is 10 feet deep or more then try and blow thru it to make bubbles.You will hurt yourself trying.Then fill the tube with water and you will notice its a lot easier to move the water.

 

[Trembull]

Fisheyes right
Water weighing in at almost 8 pounds per gallon, At 100', Pressure from the weight of the water alone would be something.. Look at Your local drinking water towers, Filled by pumps, Pressure I believe is by weight of water leaving the towers height.
In school seems like I remember them saying how they got water to and through the Time square building,Pumping it up into Tanks. The pipe joints are all welded, because there is 300 to 400 psi on the water lines at Ground level, Because of the weight of water from that height..
My Two Cents

 

[Jason in Enid]

Fisheyes right
Water weighing in at almost 8 pounds per gallon, At 100', Pressure from the weight of the water alone would be something..
My Two Cents

There is ZERO additional head pressure below the surface of the water. The only head pressure is from the deck to the water surface.

As for the need for a "house sized" air compressor, please review your math. 130 FSW depth has a pressure of 4 ATM which is 4 X 14.696 = 58.78 PSI. That's all you need to get the air to depth to go back up the expansion / suction tube. The cheapest air compressors can do that.

 

[Trembull]

YES, If your working thru a soda straw, That Cheap compressor won't have the volume to keep up with the bring up

 

[Jason in Enid]

YES, If your working thru a soda straw, That Cheap compressor won't have the volume to keep up with the bring up

You don't need a huge volume of air. A standard air hose is plenty. You aren't moving sand with air pressure, you are moving sand with the expansion of the air as it rises. Yes, you do need some volume but you are making it sound like you need some extraordinary measures and it simply isn't true.

 

[aquanut]

Jason in Enid is correct.
Aquanut

 

[Dell Winders]

Air Pressure is not the determining factor. The volume of air has to be sufficient to to expand the rising air bubbles to the entire diameter of the air lift tube. A 5 cfm compressor will not produce enough air volume to operate a 6 inch air lift. 30 cfm or more will. Dell

 

[Sommy]

So the next question is to where each type of overburden mover DEPOSITS said overburden...the airlift deposits it a little ways away...unless you have an airlift that has a section of hose attached to seperate the airlift and the intake. This is cheap and easy, but you need a few mods to the airlift, most important would be the air valve that supplies the airlift should be moved to near the intake so that you can shut it off as the need "arises".
The water dredge idea is more expensive but would not produce the air bubble cloud at the surface, would be easier to deposit the overburden further away, and would reduce the amount of suspended partcles getting near the surface...which is easy to see while using an airlift.

 

[stevemc]

Having tried to use a water pressure powered dredge, and an air powered air lift, in deepish water, the water powered dredge hose gets filled with sand, the airlift will not. That is why they normally use an airlift to work deep water sites. They wont work in shallow water. That is where a suction dredge works best. Water powered. you could use a water powered dredge to move the sand a short distance away, but not very far or the sand will fill the hose. It cant be very long. The air lift hose stays clear and you can move it a long way away by having the airlift hose go downcurrent. If you have a huge amount of water flowing in a suction dredge, you can move a ton of sand successfully, but then you have to use a monster water pump. Air is easy to pump deep, its the expansion of the air that makes it work so well in deep water, not just the air flowing. Suction dredges water doesnt get stronger as it get closer to the surface. That is why the sand piles up in the hose.

 

[Trembull]

Thanks Steve, Makes sense .. Seeing how powerful water can be by volume. I look towards that direction. Honestly haven't seen or done either way..

 

[rgecy]

The air pressure required has to be greater than surrounding and just a little bit above will not deliver the needed volume.

At 130' you are going to need more than 100psi and any where from 70-80cfm for a 4" dredge and more than 150cfm for a 6" dredge. Per Bob Marx! And thats one hell of a compressor!

I would say the water dredge would be less noise, less conspicuous. Just do like they do on gold dredges and use a suction hose with the jet located farther up the tube. It doesnt have to be at the suction nossel, but certainly cant be at the surface. Just far enough away to carry away the overburder.

Robert

 

[wwwtimmcp]

how much cfm for a 4" airlift at 35 feet ?