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Post by RKC on Nov 15, 2008 9:25:44 GMT 12
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Post by RKC on Nov 15, 2008 9:26:15 GMT 12
From: RKCNZ Sent: 24/10/2008 11:56 a.m.
G'day Dan (Dredgeotago1 ), The dredge that used two 10 hp Honda motors was a 6-inch surface dredge. Regards, Rob (RKC)
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Post by RKC on Nov 15, 2008 9:26:36 GMT 12
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Post by RKC on Nov 15, 2008 9:28:08 GMT 12
From: RKCNZ Sent: 24/10/2008 3:40 p.m. G'day Dan and Vaughan, I'm probably repeating just myself here but I will quote from a previous post I made on this forum which probably better explains what I'm trying to get across: groups.msn.com/golddredgingforum/general.msnw?action=get_message&mview=1&ID_Message=335 What basically needs to be taken into consideration by anyone making a power jet is to get the angle of the venturi right (11 degrees) and to have the diameter of the tube used for the venturi wide enough so that a significant volume of water is introduced into the power jet tube. In the article “Venturi Jet Analysis” Reggie Gould states that “the diameter of the jet (venturi) has to be the correct size in relation to the diameter of the tube that the water is flowing through. The action is fairly simple; it is the effect of a high-pressure stream of water impacting upon the column of water and material in the venturi generating tube. As the column of water moves away from the high-pressure stream of water, it leaves a vacuum behind it.” While it is true enough to state that “the jet (venturi) has to be the “correct size”, it would have been better to state that the diameter of the venturi should ‘not’ be so small that only a high-pressure stream of water enters the tube, without the necessary volume (as large a diameter as possible should be what’s aimed for, while maintaining high-pressure ).
A point that’s extremely important to consider when evaluating power jets is the necessity of using a suitable pump. A pump designed specifically for eductor/suction dredges ‘must’ be used. Only dredge pumps can produce a high volume of water at high pressure. Even a perfectly designed power jet or suction nozzle would be near useless if an unsuitable pump, such as a trash pump, is used. Using a suitable pump is so obvious and well known to experienced dredgers that its importance is not always emphasised … its another reason why production dredges should only be designed and built by experienced dredgers! Regards, Rob (RKC)
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Post by RKC on Nov 15, 2008 9:28:40 GMT 12
From: Dredgeotago1 Sent: 24/10/2008 7:15 p.m. Hi Rob Yes your sketch is what I was suggesting, I have added a picture of the venturi I use. The jet is 1" tube a Reggie Gould and many others suggest and has an ID of 22mm (or 7/8") Have a look at venturi here: thedjdan.googlepages.com/venturiCheers Dan
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Post by RKC on Nov 15, 2008 9:29:17 GMT 12
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Post by RKC on Nov 15, 2008 9:30:35 GMT 12
From: RKCNZ Sent: 26/10/2008 4:27 p.m. G'day Dan (Dredgeotago1), I had a look at the photo of the venturie on one of your 3-inch dredges thedjdan.googlepages.com/P5250026.JPG/P5250026-large.JPG and I see a venturie with an intake a little smaller than I would put on a 3" power jet ... but acknowledge that because of the type of pump you are forced to use, you probably have to have a small reduced venturie to get some punch from the pump. And I also acknowledge that the size used probably does work well enough (on a 3-inch jet). Your mistake is to use the same diameter venturie intake on larger power jets and suction nozzles ... unless I have misunderstood and you actually do use larger venturie intakes on larger dredges. It would be worth clarifying. Do you use venturie intakes of 7/8" on all the dredge size you sell? The article on Bernoulli's Principal was interesting and thanks for posting the URL.http://home.earthlink.net/~mmc1919/venturi.html Also, how do you expect a dredger to go about freeing a blockage in one of your power jets or in the green hose that is fitted between the power jet and the sluice box? And are all your power jets set up the same way as in the picture of the 3" power jet? Regards, Rob (RKC)
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Post by RKC on Nov 15, 2008 9:31:34 GMT 12
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Post by RKC on Nov 15, 2008 9:32:25 GMT 12
From: russ39 Sent: 27/10/2008 11:26 p.m. hi guys,
New Chinese motor and pump owner here.tried it out today with little success,primed it up and away we go,but it doesn't pump.will only pump if sitting in the water.intake hose appears secure.the moment you lift it higher than water level looses its suck.all front gaskets appear OK so is it possible to suck air through the back of pump?is so any thoughts on fixing it.did notice air bubbles in main suction hose when running......
Thoughts please, Russell
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Post by RKC on Nov 15, 2008 9:55:44 GMT 12
From: VJG73 Sent: 28/10/2008 12:17 a.m.
Hey Couple of things you may wish to check. Secure suction hose at foot valve and pump end with hose clips. Not to sure about what foot valve if any your running but some prone to getting small stones in them and sticking open. Especially the plastic Hansen Valve. You can loose prime pretty quickly. Sounds like you have checked the pump.. Mechanical seal in the back of the pump may have failed but I dought it already unless you have run it dry for some time. I presume they have a carbon ceramic seal assemble.. Try disconnecting the delivery side of the pump and force priming the pump . Cheers Vaughan
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Post by RKC on Nov 15, 2008 9:56:56 GMT 12
From: flapperthermal Sent: 28/10/2008 9:59 a.m. Howdy,
I'm a bit confused here now. I'm building a suction noozle for my dredge, my pump (proline) has a 2 inch outlet, so do you build a reducer into the suction noozle or not? How do Keenes build their ones?
Happy hunting Matt
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Post by RKC on Nov 15, 2008 9:59:07 GMT 12
From: russ39 Sent: 28/10/2008 9:48 p.m.
Hi there,
Me again regarding no suck motor. Well appears I've made a joe out of myself. Wire hose clips were sent with pump and used and after tightening these they were covered in tape to stop the odd sharp edge that can occur. Rechecked these today and clip on intake hose had stripped thread and has allowed tension off clamp. Henceforth pump what pumping mostly air not water.
Lesson learnt,don't use sub standard hose clips.......
happy dredging fellas... Russell
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Post by RKC on Nov 15, 2008 9:59:47 GMT 12
From: RKCNZ Sent: 29/10/2008 1:50 p.m.
G'day Matt (flapperthermal), Just to be clear ... is it a 3-inch or 4-inch (surface?) dredge you have decided to make? Regards, Rob (RKC)
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Post by RKC on Nov 15, 2008 10:00:50 GMT 12
From: RKCNZ Sent: 29/10/2008 2:45 p.m. G'day, The following is some interesting infomation on venturies from: www.cbfwa.org/FWProgram/ReviewCycle/fy2002in/projects/34020n.docAbout Venturi Eductors Venturi eductors have been used in the placer mining industry for at least 50 years. Their primary function has been as a means of vacuuming gravel from river bottoms to recover the gold contained there. Water (motive water) under pressure is introduced into the eductor tube through a venturi nozzle. This creates a vacuum at the suction side (up to 15” HG have been verified) and a positive pressure discharge at the opposite end. Since there are no moving parts in the eductor tube, gravels (or fish) can pass through the eductor without damaging it - or in the case of fish, damage to themselves. We have developed the process of using the positive side of the eductor to safely produce large volumes of water that will influence a larger volume of water (zone of influence) and duplicate or simulate bulk flow or thalweg. Initial inquiries to Keene Engineering, the leading manufacturer of suction dredges in the United State, have produced a rule of thumb flow ratio. Since the mining industry has largely been concerned with the amount of suction produced, no one has prepared graphs or flow charts for the discharge side of the eductor: hence, the purpose of this project. The “rule of thumb” as related to us is a 1:5 to 1:6 ratio of motive water to discharge water. No pressure or velocity graphs are available. Translated into real terms of water movement, this means for every 100 gallons of motive water, there would be 500-600 gallons drawn through the eductor for a combined output of from 600-700 gallons of water. This discharge is commonly achieved with a 4 inch venturi eductor. An 8 inch eductor would have a motive water imput of 400 gallons per minute with a discharge volume of 2,400 - 2,800 gallons per minute. We have been told that these figures can be extrapolated, but there is no scientifically researched data to verify this. If this is true, it can be hypothesized that large diameter venturi eductors can produce volumes or discharge of water: i.e. 32 inch eductor with motive water of 6,400 gpm has the potential output of 44,800 gpm. The larger volumes of water produced by these eductors lead us to several hypothesis: (1) That bulk flow can be simulated in a forebay or reservoir; (2) The extreme velocities produced at the center of the “zone of influence” will cause smolt to shear away, not be entrained, and thus serve as a velocity “curtain”. (3) That the smolt will entrain in the fish friendlier, thalweg like velocities to the side, for guidance to SFBís; and (4) That turbulence can be engineered and/or directed to provide a multi-sensory approach to smolt guidance. Regards, Rob (RKC)
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Post by RKC on Nov 15, 2008 10:01:31 GMT 12
From: flapperthermal Sent: 29/10/2008 9:57 p.m.
Hi Rob,
My dredge is a 4 inch surface machine. I'm looking at a couple of small water ways to dredge so a suction nozzle appears the way to go, any tricks to building one?
Regards Matt
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