Prospector's Library

Learn: 'How Do Suction Dredges Work?'

How does a gold dredge suck up gravel? Also learn the differences between a power jet and a suction nozzle.

Suction dredges utilize a high pressure gasoline powered water pump to suck up water, gravel and gold and inject this material into a sluice through a header box. The header box dampens the rush of water and gravel so that it flows evenly into the sluice. The sluice box then expels the worthless gravel and retains the gold. I get a lot of questions about how a gold dredge can literally suck up gravel from the bottom of a stream without the gravel going through the gasoline powered pump, which would destroy the pump. The answer is that a device is used to convert the pressurized water discharged from the pump into a vacuum. This device can either be a power jet or a suction nozzle. These two devices work the same but are configured differently.

A power jet is attached directly to the header box and the pressurized water from the pump is injected into the power jet and that the water is blown directly into the header box. This causes a vacuum to form in the material hose which sucks up water and gravel from the other end of the hose, and they are likewise sucked up into the header box. The header box is simply a deflector attached to the end of the sluice which dampens the force of the water and gravel so that it flows evenly out of the sluice. The sluice captures the gold behind the riffles exactly like it would when you use it as a stream sluice.

A suction nozzle works in a similar fashion except instead of being attached directly to the header box it is attached at the far end of the material hose. A vacuum is created which sucks up water and gravel but the material is pushed through the hose instead of being sucked through the hose, as in the case of the power jet.

So, which system is better?

The answer is that they each have advantages and disadvantages. The advantage of the power jet is that the operator of the dredge has to only deal with one hose when he is dredging. The power jet also allows deeper dredging because the power jet will lift material higher than a suction nozzle can push it. The disadvantage of the power jet is that the power jet and supply hose must be kept under water at all times. Therefore they do not work very well when working in shallow water. The advantage of the suction nozzle system is that you can dredge in very shallow water and walk around with the suction nozzle completely out of the water without effecting the performance of the sluice. The disadvantage is that you have two hoses that the dredge operator must deal with. Generally speaking a dredge designed to work on flotation, with a compressor for underwater dredging, is almost always equipped as a power jet. A dredge that is designed to work with the sluice on a stand, in shallow water, is almost always equipped with a suction nozzle. If you are using a high banker dredge combo with multiple uses you can also purchase the power jet and suction nozzle so that it can be used with either configuration depending on the application.

4/17/2014 11:25:53 AM