Therefore most dredge permits refer to the nozzle size, not the hose size, when imposing rules and restrictions. The volume of material processed is determined by the nozzle opening, not the inside diameter of the hose. A 5' dredge may have a nozzle opening of 4' for this reason. However, nozzles are used on dredges which restrict the intake to a size smaller than the inside diameter to help prevent clogs. So a 5' dredge has a main suction hose with a 5' inside diameter.

Manufacturers rate suction dredges by the inside diameter of the main suction hose. Floats are also needed because there is rarely a nice gravel bar in just the right place to set up a dredge without floats. Every inch of vertical lift above the surface of the water robs power/suction from the system. This is because a dredge has just enough power to lift water and gravel to just above the surface of the water. Dredges almost always need to be mounted on a set of floats. A sluice box works because gold is 15 times heavier than sand and gravel and so is easily trapped by the riffles and carpet in the sluice box. Material is transported from underwater to the surface and run through a sluice box to capture the gold. I made a removable restriction nozzle so I could get my hand in to clear blockages, and for easy replacement as it wears out.A suction gold dredge is basically an underwater vacuum cleaner. The water was only 2 feet deep where I was working, but the old venturi did not have had that sort of power. The result was great, power increase was such that the water and gravel came up the hose with such velocity at high rpm, that it shot right over the sluice box and landed back in the creek 2 feet beyond it! I had to slow it right down to be able to wash the gravel. I will try to load 2 photos showing what I came up with.

I used alloy for weight reasons, but also because it was what I had on hand. I lined up the new 3/4 inch jet to be slightly pointing downward but up the center of the pipe - so the water jet would hit the bottom of the pipe about 3 or 4 feet up. Mostly because my hand wouldn't fit up past the nozzle restriction. The old shop bought venturi had worn totally out and was very hard to get jammed rocks out of. My pump is a 5 hp Honda driving an Onga pump - a factory built pump/motor unit available here in NZ. The last one was four inch and I used a 3/4 inch jet with a flare out to the 1 1/2 inch supply.

Hi there, I have made a few suction venturi nozzles over the years, as I couldn't find or couldn't afford store bought.

Dredge nozzle design