1. SUCTION DREDGE OPERATION
Placer Examination Techniques

2. Suction Dredging is…
The activity of sucking material with a gas propelled pump and depositing it on a sluice to collect the heavy material, or…
Underwater vacuum cleaner.

3. Dredge Size Rated by the size of the intake nozzle.
Range: 2 inch to 10 inch diameter intake.

4. 2 and 2 ½ inch dredges “Backpack” dredge Carried by 1 person
Small drainages
Poor access
2.5 hp engine
50-90 lbs.

5. 3 inch dredge Shallow drainages
Sniping along banks of larger streams and rivers
5 hp engines
20 – 35 foot intake hose
150 – 200 lbs

6. 4 inch dredge Common size 1 to 2 person operation
1 person can haul once partially disassembled
5 – 8 hp engine
20 – 30 foot intake
200 – 250 lbs

7. 5 inch dredge Common size Single 8 – 11 hp engine, or
Dual 5 hp engines
Disassemble to transport
30 – 40 ft hose
Assembly time: ½ to 1 hour
300 – 400 lbs

8. Dredge Production Manufacturer estimated production
Production based on experience
4 inch dredge
5 yards/hour
1.6 yards/hour
5 inch dredge
10 yards/hour
3 yards/hour
6 inch dredge
15 yards/hour _
8 inch dredge
25 yards/hour

9. HOW IT WORKS Engine drives a centrifugal pump and air compressor
Pump drafts (pulls) water and forces it into a pressure hose
Pressure hose is a direct path to the intake hose and causes a suction (venturi effect)
2 different configurations
Suction nozzle
Power jet

10. Suction Nozzle

11. Power Jet

12. Advantages – Which is better?
Suction nozzle
works better in shallow water
Power jet
Creates a stronger suction
Fewer hoses at the “working end”

13. Baffle Box

14. Clean-up Coarse pieces are picked out of the sluice on a daily basis.
Concentrates are washed out of the sluice on a daily or weekly basis
Exams: sluice is cleaned after each sample

15. Clean-up
Concentrates (black sands) are processed by panning or using a concentrating device such as a gold screw or gold wheel
Very fine gold will require mercury amalgamation

16. AIR
Hooka – low pressure air system using an air compressor feeding air lines and delivering air to the diver through a regulator.
Air tank partway through the circuit supplies a constant volume or air, regulates the feed, and is an emergency supply if the compressor fails.
Regulator – one way valve delivering a low pressure air supply on demand