Operating a Portable Dredge How a Dredge Works Before you Buy: Research dredges and
dredging laws by reading and watching videos Procure a claim, or
club membership with claims where dredging is allowed
Dredges work by creating a powerful vacuum from water forced at a high velocity, through a tapered jet. Water and gravel from the bottom of streams or lakes are vacuumed into a suction hose and delivered onto the sluice jet flare and are distributed along a classifier screen. Smaller and heavier particles drop into riffles, or become trapped in the miners moss, carpet, or other material designed for this purpose. Lighter and larger aggregate are returned back to the water. The force of water flowing over the riffles allows heavier material
to settle, while the lighter material is washed away. This continuous self-cleaning allows for prolonged dredge activity. The sluice would need to be cleaned only once or twice in the course of a normal dredging day. Before starting the engine, the pump must be fully primed, meaning it must be full of water, and air must be removed. On smaller models, thrust the foot valve back and forth, under water, in a reciprocating motion until you can see water flowing out of the discharge end of the pump. On larger models with a rigid foot valve, remove the cap and fill to overflowing, taking care to keep out any sand or debris. You can put the intake portion of the foot valve in a bucket placed under water to keep sand out during operation. Priming the suction hose is not necessary, but you should know that when the tip of the suction hose is taken out of the water during operation, air will enter the suction system and cause suction to cease until it’s resubmerged. Suction will commence as soon as all the air has passed through the system. Make sure to patch any air leaks. To avoid jamming the vacuum, see that mostly water is being vacuumed and solid material being dredged never exceeds 10% of the total volume. Most jams can be cleared by flipping the rubber damper back and using a probe to loosen solid material. If the suction hose becomes jammed, the hose may need to be removed in order to get it dislodged. If the adjustable sluice box isn’t at the right angle, it could overload and riffles will fill with excess material, or material will flow too fast, causing material to be lost back into the water. A normal tilt angle is about ¾” to the running foot. A 4-foot sluice box should have an approximate tilt of 3”.
Dredging Essentials: Use an air filter and change it once a year, minimally. Use a spark arrestor. Change the oil after 5 hours for a new motor and every 20-25 hours after that, using the weight specified for the motor. Avoid condensation by topping off the gas tank after use and never leaving it empty. To store in the offseason, first add a fuel stabilizer, hook the pump to a water supply, and run 5-10 minutes.