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The Pocket Sluice

Author Topic: Pinched sluice  (Read 10209 times)

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Offline rockpup

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  • Yar der be gold in dem pans!!
Pinched sluice
« on: April 21, 2009, 07:39:29 PM »
Here is a Forgotten piece of placer mining equipment.Everyone talks about fine gold recovery,I am very surprised no one has thought of using one of these.It is very straight forward,would be a easy home bulid.It would take some time to design a splitter but the concept is real simple.Very simple,cost-saving,cheap.I am going to have to look around for some more information on this.

The Pinched Sluice: A high capacity concentrator that will catch fine grained gold is called the "pinched" sluice. It uses another concentrating approach to improve upon the sluice box.


Fig. 4.5: Plan and Sectional diagrams of a pinched sluice, showing the separation of high density material from low and medium density material at the end of the sluice.

Particles on the bed of a sluice box have a lifting force on them similar to aerodynamic force. The velocity of water is higher at the top of the particle than at the bottom. This velocity shear creates a lower pressure area at the top of the particle that "lifts" it up. The particle is then carried downstream until it again hits bottom.

This process is called saltation. It is repeated over and over until the particle leaves the sluice box. Particles of high specific gravity have lower lifting force per unit mass and tend to stay close to the bottom, producing a layered effect. If the pinched sluice has laminar flow, the layers become well defined, with virtually all the heavy minerals on the bottom.

When such a sluice is narrowed or "pinched" at the downstream end, the depth of the flow is increased making the layers easier to separate into concentrate and tailings. Particles larger than 1.65 mm (.06 inches) tend to roll rather than jump. This destroys the layering effect, making classification necessary to keep the layers stable. The pinched sluice must be operated with an even, dense feed. If this is done, very high recovery rates may be achieved.

Offline GollyMrScience

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Re: Pinched sluice
« Reply #1 on: April 21, 2009, 09:54:31 PM »
 A pinched sluice is most often used as an upgrader and is not usually a final recovery system like a sluice is. I have seen systems that use a series of pinched sluices to upgrade further at each step. It can be very difficult to get a good clean split in a sluice type system as there is drag fro the sides of the trough. This interferes with the clean flow and the resulting efficiency of the split.
Feed can be a trick - don't want to cause duning in the trough but have to balance slurry ratio well.

If you are willing to deal with a larger cons volume the pinched sluice can be used as a primary concentrator but you will have a lot of con to deal with and the separation system will have to be upgraded to a great extent.

A modern analog would be the Reichert Cone. Its design gives the same effect but cones can be stacked to get more work out of less floorspace and they can be configured to redo mids to upgrade them further to a con with cleaner tails as a result. They also suffer less from the problems that sluices do as they dont have the side drag effect or the duning problem or potential.

They still need some careful classifying and slurry control though.
What the heck - lets just keep mixin' stuff together till it blows up or smells REALLY bad!

Offline Vagadero

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Re: Pinched sluice
« Reply #2 on: January 24, 2010, 03:00:03 AM »
How they are looking? Does anybody have pics, please?

Offline GhostRyder

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Re: Pinched sluice
« Reply #3 on: August 25, 2010, 10:31:37 PM »
New miner here.  I was looking at the pinched design and it seemed to be the answer to both coarse and fine gold
recovery.  After reading the way the sluice works this might end up being more work than my idea of a 1/2 grizzly,
boiler box and sluice.

Thanks for all your input and insight everyone.  This is a new hobby to me and I would rather not take my normal
approach to hobbies and just jump in with a lot of cash.  Retired now and have a lot of time for tinkering and building
my own gear.  That's more that half the fun.

Offline GollyMrScience

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Re: Pinched sluice
« Reply #4 on: August 26, 2010, 07:07:17 AM »
The pinched sluice is more "finickity" than a regular sluice - demanding carefully classified and consistent feed. Not very forgiving and unless going to a further upgrade step you will find the concentration ratio will create a significant volume of concentrate that has to be dealt with.
A regular sluice is a displacement system and operates in a batch type mode. In a displacement system like a sluice there is a limited area for concentrate retention and as new material is added if the retention area is full then the action in the unit will cause heavier minerals to displace lighter ones but still keep the volume of retained material essentially the same.
This process will go on with usually diminishing efficiency until losses of desireable minerals become unacceptable. At that point the unit is shut down and that batch cleaned out.
The concentraton ratio can be very high. Often in  the order of a hundred to one or more.
Because you are dealing with a fixed volume and that volume gets richer the longer you run the cons will reflect that. Consider a sluice that has about one gallon of retention volume. Within the first five minutes that volume is essentially full of something. Whether you shut down in five minutes of five hours the volume will remain the same but the amount of gold that will be in that fixed volume increases. This becomes real handy when it comes time to get the gold out of the con. Way less material to handle and the seperation system can be sized accordingly.
Now a pinched sluice uses displacement in the bed to enrich the con but it has a continuous bleed of cons from the sluice. The concentration ratio is a function of sluice design and feed but once that is set the sluice just keeps spitting out cons and the concentration ratios are low compared to the batch systems.
Concentration ratios are good at 10 to one. That means the volume of cons to deal with can be 10 times or more the volume of cons from a standard sluice.
Where a hand mining sluice operator could keep up with the cons produced with a miller table the pinched sluice operator will have to consider upgrading their seperation system to a vibrating table. The standard sluice operator might have two five gallon buckets of cons to deal with after a long day the pinched sluice operator would have two 50 gallon buckets even though they ran the same volume of head feed.
This is a simplified illustration but illustrates why standard sluices are so popular and why pinch sluices are rarely stand alone systems. They serve more as roughers and then feed their con into another system to further upgrade. Gets to be too much for a small operator, especially if they are trying to stay small, light and inexpensive.
What the heck - lets just keep mixin' stuff together till it blows up or smells REALLY bad!

Offline drpop

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Re: Pinched sluice
« Reply #5 on: August 31, 2010, 07:53:07 PM »
would a pinched sluice work well on the beach to feed a beach box. Would a shovel full at a time be constant enough.   



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