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Dredge Overloading
Overloading happens when there is a lot of weight in the material that is getting dredged to the point in which it is so much that it does not allow lift and successful sluicing. This does not usually happen in water that is waist high but when you are working in depths that can be dived in or that go further than six feet it begins to occur more often.
You can in most cases detect the first indication of overloading at the suction nozzle and not in the sluice. The suction at the nozzle is highly reduced and the amount of gravel gets to be too much than the dredge is able to handle. When the problem is very big, overloading is able to cause cavitation at the base of the jet. There is most likely not any amount of sand that can be so great that it could change the pressure gain at the nozzle so that the sand flow back into the low end part of the suction tube.
The thing that occurs in overloading is that gravel and sand cause high frictional forces inside the tube that can turn into such a great amount that the movement of the stream is slowed down. On occasions this effect can be very pronounced and the suction at the nozzle almost stops. This problem can be observed more in the fixed ejector close to or on top of the surface type, and usually always happens in depths that are above ten to fifteen feet.
The way to resolve this is pretty easy, all you have to do is back the suction nozzle away from the gravels and let more water go up to the suction tube until the fraction of water to the gravel is augmented. The speed inside the suction tube will quickly speed up and the gravels will begin to move again. You will be able to notice by looking at the suction nozzle. It is a sign that you have been attempting to suck up too much gravel in the tube and in order to prevent it from occurring again you just have to increase the distance of the tipi from the gravel by a little bit. After you are able to see the gravels moving inside the tube regularly at around the same speed, you will be able to tell that you have located a good distance of suction for the kind of material you are dredging.
There is also another type of overloading that occurs sometimes however it is a bit trickier to detect by the suction tube operator since it does not always show itself in a very reduced type of suction. It occurs when the overloading takes place between the bottom of the jet and the pressure box. Due to the fact that the base of the jet will always generate a good amount of suction, the sands and gravels will keep on flowing in however they will not be sped up as much when the jet travels back up to the pressure box. With very increased sand in comparison to the water, the riffles will get plugged up quick rapidly and all the values inside will be washed out through the sluice.
