GENERAL OPERATING
INSTRUCTIONS
THE FOLLOWING INFORMATION SHOULD ENABLE YOU TO UNDERSTAND THE
BASIC THEORY OF OPERATION OF A PORTABLE DREDGE.
For more complete understanding on this subject, we recommend you read any
one of a variety of books available through the Keene Library of Books, such as The Gold
Miners Handbook, Dredging for Gold or Advanced Dredging Techniques. The vacuum on a
portable dredge is created by a "venturi principal". A volume of water is pumped
through a tapered orifice (jet), by a special designed water pump. A high velocity jet
stream is created within the jet tube producing a powerful vacuum. As indicated in the
diagram gravel is dredged into the suction hose and is delivered to the sluice box header.
As a slurry of water and gravel enters the header box and is spread evenly over a
classifier screen. The smaller and heavier particles drop below the classifier screen into
an area of less velocity, allowing a slower and more selective classification of values.
Often values are recovered and easily observed before they even enter the riffle section.
The lighter non bearing values and larger aggregate are returned back into the water. The
riffles, or gold traps in the sluice box are best described as "Hungarian
Riffles". This type of riffle has proven to be the most efficient gold recovery
system. As material flows over the riffles a eddy current is formed between each riffle
opening. This force allows the heavier material to settle out of suspension and the
lighter, non value bearing material to be washed away. This continuous self cleaning
principal allows a dredge to be operated for prolonged periods of time. Normal conditions
require a sluice box to be cleaned only once or twice a day.
PRIMING THE PUMP
Before starting the engine, the pump must be fully primed. This means the
pump must be full of water and all air removed. All jetting pumps provided with our
dredges have a mechanical water pump seal. Without the presence of water in the pump,
friction could cause a seal to overheat and require replacement. Priming the pump on some
of the smaller models is accomplished by thrusting the foot valve back and forth under the
surface of the water in a reciprocating motion. This will cause water to become pumped
into the foot valve assembly into the pump. A pump is fully primed when water is observed
flowing out of the discharge end of the pump. It sometimes may become necessary to hold
the discharge hose above the level of the pump to complete the priming operation. The
larger dredges that have a rigid foot valve, are easily primed by removing the cap
provided on the foot valve and filling, until water overflows. Caution must be exercised
to prevent sand from entering the foot valve or intake portion of the pump. Excess amounts
of sand could dam age the water pump seal, or pump impeller. It is recommended that the
intake portion of the foot valve be placed in a sand free environment underwater, such as
a small bucket or pan.
PRIMING THE SUCTION HOSE
Priming the suction hose need not be of concern in most dredging
operations, but is important to understand the principal. When the tip of the suction hose
is taken out of the water during operation air will to enter the suction system and cause
the suction power to cease temporarily, until submerged again. The suction will commence
as soon as the air is passed through the system. It is important to ensure that no air
leaks occur in the suction system.
SUCTION SYSTEM OBSTRUCTIONS
The suction system can become jammed while dredging. This can be caused by
dredging an excess of sand, causing the suction hose to load up, or a rock that has become
stuck in the suction system. Rock jams generally occur in the jet, or just before entry
into the jet. This can easily be cleared by removing the rubber plug located on the front
of the header box and thrusting the probe rod through the header box and down through the
jet in an effort to strike the obstructed area. It may occasionally be necessary to remove
the suction hose to remove an obstruction. Sometimes obstructions can easily become
dislodged by back flushing the system. Back flushing a suction system can be accomplished
on some models by reversing the flow of the suction hose at the header box, by blocking
the flow of the water as it enters the header box. If this is not successful. it may be
necessary to locate the blockage in the transparent hose and dislodge it by a striking the
obstruction, taking care not to damage the hose.
SOLID CONTENT
Care must be exercised to prevent dredging excess amounts of sand. A solid
to water balance must be maintained. The solid content being dredged should never exceed
10%. If a suction tip is buried into the sand and not metered properly the solid content
could cause the suction hose to become overloaded with solids and suction will cease, this
will also cause the sluice box to become overloaded with solid content, resulting in a
loss of values.
SLUICE BOX ADJUSTMENT
Most models have a slight adjustment to raise or lower the sluice box. The
proper sluice box adjustment can effect the recovery of values. If the sluice does not
have enough angle, the sluice box will "load up" causing the riffle openings to
fill with unwanted excess material. Too much angle will cause the material to flow too
fast, resulting in loss of values, evidenced by the riffles running too clean. The optimum
adjustment of a properly working sluice box is evident by only a portion of the riffle
visible while operating. A loss of values can also occur if the solid content of the
suction discharge is too heavy in solid content. Remember, the solid content should not
exceed 10 %. A normal sluice box tilt is approximately 1/2 inch to the running foot. A
four foot sluice box should have an approximate tilt of 2"
CLEANING THE SLUICE BOX
Before attempting to clean the sluice box, it should be allowed to run with
only water for a few minutes in order to wash out any excess gravel that have accumulated.
Either turn engine off, or let run with a slow idle, then remove the classifier screen and
replace the wing nut to prevent losing it. Unsnap the riffle latches, fold the riffle tray
up, and let rest against the header box, taking care not to let it drop back into place
while cleaning. This could result in a potential injury! Place a wide tray, bucket or
large gold pan at the end of the sluice, then carefully roll up the riffle matting and
wash into the container at the end of the sluice. Rinse any excess gravel that remains in
the sluice into container. All material must be removed before replacing the riffle
matting, riffle tray and classifier screen.
ENGINE SPEED
Most small engines are throttle controlled. The speed of the engine can be
controlled with the use of a lever. Although the rated horsepower is achieved on most
small engines at 3600 R.P.M., it may not be necessary to operate the dredge at full speed.
Lower speeds conserve engine life and fuel economy. Be sure to read all instructions and
especially the engine instructions that are provided with each unit. ENGINES ARE NOT
SHIPPED FROM THE FACTORY CONTAINING OIL. OIL MUST ADDED PRIOR TO USE! ENGINES OPERATED
WITHOUT SUFFICIENT OIL SUPPLY WILL INVALIDATE ENGINE WARRANTEE!
TROUBLE SHOOTING
[A] IF SUCTION DECLINES
1. Check the suction device for an obstruction. An obstruction can be
removed by probing the obstructed area with the provided probe rod. I may be necessary to
check the suction hose for a visible obstruction. This can be remedied by either back
flushing the system or dislodging the obstruction with a gentle blow.
2. Check the pump for loss of prime or blockage. The foot valve may be too close to the
surface of the water and air may enter the intake of the pump via a small whirlpool. The
pump intake or foot valve screen may be plugged with leaves or moss, restricting flow into
the intake of the pump. Check and tighten all clamps to prevent an air leak.
IF PRIMING THE PUMP BECOMES DIFFICULT
1. Check all clamps for an air leak.
2. It may be necessary to check the foot valve for a small leak. This is accomplished by
removing the foot valve assembly from the pump and blowing air into the hose portion of
the assembly and listening for an air escape. It may be necessary to remove the hose and
check the rubber valve for an occurrence of a leak, or for a small obstruction preventing
the valve from sealing.
3. If a water pump seal is either defective or damaged, a leak will be evident on the
inside portion of the pump around the drive shaft. Often a new pump will leak slightly,
until the seal and gasket has become fully seated. This is a common occurrence in most new
pumps. |
