Underwater Dredges and Sluice Boxes

There are other drawbacks when it comes to the underwater dredge. Some of them are difficult to use around or under boulders. Besides that due to the fact that the discharge point is much closer to the person operating it he will often times find he has to dredge some of the tailings again if he is working in an widespread overburden. Nonetheless, non of these problems are terrible issues to handle when you compare them with the amount of time you are saving in removing a large quantity of overburden and a lot of bigger operations use the combination dredge in order to get bigger jobs done.

In theory an underwater dredge has an unlimited depth and sometimes it is the only type of dredge that can be used by a scuba diver. The centrifugal pump is supposed to pump water to any depth making sure the pressure of the water does not make high pressure hose or suction tube collapse. This would be at more of a depth than a diver could work anyways, and the underwater type sluice can be considered useful for any depth you need. There have been cases in which gold was recovered from depths of sixty feet and more in some cases.

One of the good things of owning a fixed ejector sluice is that later on when it time requires it, the underwater sluice and longer high pressure hose can be added and it will not cost a great amount.

The initial idea from the underwater dredge was to connect the ejector to a sluice on the surface and this is the closest that modern dredges have come to the hydraulic elevator that used to exist in the past and the only actual difference is the ejector that can be moved.

When it is done this way, the jet goes into the tube right on top of the head of the suction nozzle and the jet is supposed to move the whole column of water in order to get some momentum from the stream. This sucks up energy a lot quicker than the higher mounted ejector does for the simple reason that there is now more entrained water for the jet to be able to push.

One good and advantageous aspect about this type of operation is that the weight of the water that is inside the tube from the bottom of the jet to the mouth of the nozzle does not cause as much pressure outside of the tube in order to make the water go in at a quicker speed. This is definitely a plus, however it is not sufficient to beat the loss of energy higher in the tube. For the same length of suction hose the higher mounted fixed ejector is a lot better and useful.