subsea dredge pump system

want to build a 4 inch dredge.

Post by diamenia

Hi everyone, I am diamenia, live in the republic of Liberia and want to build my own gold dredge. i have a 4" Robin firefighter engine/water pump and want to use it to build my dredge, can any one help me with ideas for the construction of my dredge? Diamenia

Post by RKC

G'day Diamenia, To answer your question in detail you can find a previous thread at the following link ... ( Building a small dredge ). But before you start, and go to the trouble of building a dredge, I suggest you first give some consideration to the size of dredge you should be building. A four inch dredge is essentially a recreational dredge and if you build a dredge this small you will be extremely restricted as to what you will be able to do. I don't know what you have in mind to dredge but as you are in Liberia my guess would be that you want to do some commercial-scale serious profit-orientated dredging! Here in Australasia a dredge this small would rarely be used by serious dredgers ... they would only be of use to a professional in rapids to clean out exposed crevices with little overburden to remove. They can be used to sink prospecting holes, however the holes would not be deep enough in most rivers to prove anything conclusive. Where the overburden above bedrock is more than a few feet deep, as it is in most auriferous waterways, these dredges won't get a prospecting hole down as far as bedrock. And, if the water depth from the surface to the top of the river gravel is more than a meter, most 4" dredges won't be of much use. If a professional dredger wants to prospect an area of interest by sinking numerous prospecting holes, and who needs a dredge small enough to be portable, he will chose a 5" over a 4" every time. Even a 5" dredge has its limitations for prospecting ... a 6" dredge is a better choice if the waterway to be prospected is big enough to allow it to be maneuverable. If you are going to dredge a waterway of a fair size where the overburden above bedrock is more than a few feet deep, you would be better to make a 6" dredge. With a 6" you can do a lot of prospecting and can also do some production dredging immediately after the prospecting phase has ended. Regards, Rob (RKC)

Post by diamenia

Hi Rob, many thanks for the useful information given me. Right now the only thing about the dredge is the price. A 6 inch dredge is very expense to buy, this is while i am looking to build a 4 inch. I have a 4 inch Robin water pump engine/motor, Is it ok to use any water pump/engine to build a dredge? or is it special water pump/ engine to be used to a dredge? Rob your advise is really needed, please. regards, Diamenia

Post by RKC

G'day Diamenia, I would never personally use the type of pump you have, on a gold dredge! But ... I can understand you might have difficulty sourcing correct equipment in your country. So, if that's the way you have to go then do it (its always better to do 'something' than give up and go home . The pump is the heart of a gold dredge, and the pump used on any dredge should be one designed specifically for gold dredging. If a pump is used that is not specifically designed for dredging then you are creating an unnecessary difficulty right from the get go. The following is what has been previously posted in this forum about dredge pumps ... _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! I had a look at the pumps on your web site and the pump on your 4-inch dredge is simply a Chinese knock-off of a standard Honda water pump which is designed to move water in volume. These Chinese pumps are designed for a very different job to the pumps designed specifically for eductor dredging. Eductor dredge pumps move water at high volume COMBINED WITH high pressure. I can't imagine how these Chinese pumps could even come close to doing the job required of a dredge pump. The issue of dredge pumps has been refered to previously in other posts on this forum and I won't add any more except to emphasize, for any other members building a dredge, that the selection of a pump designed specifically for eductor dredging is essential on any eductor dredge (even recreational dredges) and the pump is probably the most important individual component of an eductor dredge. Using a Chinese high-volume water pump on a dredge would immediately be seen by most potential customers as a design compromise and this is probably why they are asking for pumps such as the Keene pumps. All the dredges any potential customers have previously seen would have been viewed in catalogues and on the Internet, and all would have dredge pumps used on them. The only place a dredge can be seen with a below spec water pump on them is on Trademe in New Zealand. There is a reason why all established dredge manufactures only use pumps specifically designed to use on eductor dredges._ Regards, Rob (RKC)

Post by lbd

i have a 4" Robin firefighter engine/water pump and want to use it to build my dredge, Hi Diamenia You mention having a 4inch robin pump/motor. Can you advise what size motor is driving the pump? I ask because a 4 inch pump could run a 6 inch dredge, depending on a few things.... a 4 inch pump may be too big for a 4 inch dredge Cheers

Post by diamenia

Hi every one, Sorry for not coming back to the forum for the passed few weeks due to high malaria plus to i had. i just getting back from the hospital. As i am thinking about building a dredge, I want to know what size of dredge pump can i use to build a 4 inch, 5 inch and 6 inch. the Robin 4 inch water pump I had is not suitable for dredge as i was advised. now if I am building a 6 inch twin engine dredge what size of pump can i use? a local welder in my area had promised to build me the power jet and flare jet. which web site can i buy a used pumps? new one will be very costly, I need your help. Thanks, Diamenia

Post by lbd

Hi Diamenia... You say _"build a 4 inch, 5 inch and 6 inch"_ Your 4 inch pump may be suitable for a 6 inch dredge...what are the pump details? Any second hand pumps in NZ would not be worth shipping to Liberia...you would be best to look at your industrial areas in your country to see what is available. have a look at this website...it will help you match pumps to dredge sizes...

Post by diamenia

Hi Sir, I would like to use a 200 GPM Direct Mount Pump, which goes on 3 to 6.5 HP engine. will this be OK? Thanks, Diamenia

Post by vagadero

Does anyone have a 4" suction nozzle at hand? What is the (nominal) outside diameter of the pressure pipe welded? According to the calculations an sch 40 1" steel pipe (OD 1.32" ID 1.05) should be fine. However I'm still unsure. So is that right?

Post by RKC

G'day vagadero, Suction nozzles and power jets are, without a doubt, the most problematic dredge parts for a home build dredger to construct. Most dredge builders would be far better off to buy a power jet or nozzle from an established dredge manufacturer. I can't add any more about building a nozzle or power jet than what has been previously written in this thread. If you decide to go ahead and build your own 4" nozzle you will mostly have to consider the design of the reducer that goes in the "pressure pipe" you refer to. The following is from the above thread I am refering you to. _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)