Frequently Asked Questions About The Piranha Diver Cutterhead
- What is the Piranha Diver Cutterhead [PDCH]?
It is a
hydraulic powered mechanical excavation tool. It is not a pump.
- 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.
- 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.
- 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.
- 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
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.
- 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 10fps.
[3-mps] to 13fps. [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.
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.
- 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.
- 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
- 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
gpm: Gallons per minute
psi: Pounds per square inch
cyh: Cubic yards per hour
fps: Feet per second
Liters per minute
cmh: Cubic meters per hour
mps: Meter per second