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Piranha Diver Cutterhead

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Frequently Asked Questions About The Piranha Diver Cutterhead

  1. What is the Piranha Diver Cutterhead [PDCH]? It is a hydraulic powered mechanical excavation tool. It is not a pump.
  2. What types of material will it handle? Soft to stiff mud. Material that when squeezed with your hand, will extrude from between your fingers. Material, that is harder than mud, will require careful analysis as well as larger hydraulic motors with additional torque. Contact Dredging Specialists for assistance in evaluation of hard material.

    Mud is a fine grain size, cohesive material. This means that the particles stick together. The opposite is sand, where the particles do not stick together. In sand and other free flowing, non-cohesive materials, the Piranha is not needed. Straight suction from a centrifugal pump is the best dredging method for sand.

  3. How deep can I dredge with the Piranha? There is no limit. If a hydraulic leak would develop inside the housing, the housing could become pressurized and burst. To prevent the Piranha housing from becoming pressurized, a vent hose comes to the surface. Air pressure is introduced into the vent hose to compensate for the water pressure that is outside the case. Down to 100-ft.[30-m], compensating air is not needed. Below 100-ft. [30-m], the compensating air pressure is adjusted to the same pressure as the water.
  4. What type of hydraulic power unit is needed? A minimum flow rate of 2-gpm. [7.5 Lpm] with capability for 2,500 psi. [172-bars] with a 5-hp. [3.7-kW] driver. A maximum of 5 gpm. [19-Lpm] with capability for 2,500-psi. [172-bars] with a 12-hp. [8.9-kW] driver.

    A larger power unit can be used, if a bypass flow control valve is used to limit the flow to 5-gpm. [19-Lpm]. Contact Dredging Specialists for proper set up.
    The power unit can be powered by a gas or diesel engine or an electric motor.
  5. What kind of pump is needed? A centrifugal pump with a flow rate of 400-gpm. [1,500-Lpm] to 500-gpm. [1,900-Lpm]. A jet pump, [sometimes called a venture pump], can also be used.

    Higher flows will not improve or limit the production of the PDCH. Higher flows will only waste fuel.
    If the depth is less than 15-ft. [4.6-m], and/or, the suction hose is less than 40-ft. [12-m] long, the pump can be mounted above the water. If the depth is greater than, or the suction hose is longer than listed above, the pump should be submerged.

    Pumps mounted above the water can be driven by gas or diesel engines or an electric motor. Submerged pumps are driven by electric or hydraulic motors. One of the keys to high production is to keep the suction hose as short as you can.
    The particle size that will pass through the pump is important. Select a pump that will pass as large a particle as you can.
  6. What size suction and discharge hoses do I need? If you are rigging up specifically for the PDCH, use 4-in. [10.2-cm] suction and discharge hose with the flow rates recommended above. This will provide a velocity of 10–fps. [3-mps] to 13–fps. [4-mps] in the suction and discharge hoses. This will prevent sand or other material from settling out and causing a plugged line. It will also provide good production. Now, if you have a larger pump, and say 6-in [15-cm] hose, go ahead and use them if you maintain the recommended velocity.
  7. Dredging Specialists will be happy to assist you in the selection and set up of the proper hydraulic power unit and the pump, and pipeline.

  8. How much production can I expect? Our tests show that in stiff mud, you can get 14 cubic yards, per dredging hour [10.7-cmh]. This is 233% of a diver using straight suction in the same material. If you are bidding work and without experience using the PDCH, we recommend that you use 80% of this figure.
  9. What is the size of the PDCH? As the diver holds it, it is 22-inches [56-cm] from left to right, 14-inches [35.6-cm] high and 9-inches [22.9-cm] thick. The weight is 93 pounds [42.2-kg] above the water and 5-pounds [2.3-kg] of buoyancy in the water. Weights can be added to provide the buoyancy or weight desired
  10. Does the diver get tired using the Piranha? No the divers report no more effort than using a suction hose.
Glossary of acronyms
PDCH: Piranha Diver Cutterhead

hp: Horsepower

gpm: Gallons per minute

psi: Pounds per square inch

cyh: Cubic yards per hour

ft: Feet

fps: Feet per second


kg: Kilogram

Lpm: Liters per minute

cmh: Cubic meters per hour

mps: Meter per second

cm: Centimeters

kW: Kilowatts

bars: Pressure

m: Meters]