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Post by RKC on Nov 15, 2008 9:05:04 GMT 12
From: alluvial0 Sent: 9/10/2008 9:42 p.m.
Hi there Dave, Could you put a picture up of your Brown Bros pump? You may have seen the other posts on Brown Bros pumps & the Imporium pumps.
Cheers
Regards
Alluvial
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Post by RKC on Nov 15, 2008 9:05:47 GMT 12
From: RKCNZ Sent: 12/10/2008 4:38 p.m.
G'day Dave (davec761),
I very much doubt there would be any noticeable improvement in running the pump you have now (blue pump aka Brown Bros pump) off a 6.5 hp motor instead of the 5.5 hp motor you are presently using.
If you really want to get into good gold, my thoughts would be that you should stick to using the 5" suction hose (rather than going down size to a 4" hose) and just increase power. You could do this most simply by adding another motor/pump ... so you are running, say, two 5.5 hp motors (of course this would then probably mean you would have to increase the size of your dredge by adding more flotation, change the power jet and so on ... but there are minimum requirements that can't be avoided if the aim is to get gold in payable quantities). But, if you decide that going to a dredge that is larger in overall size would not be worthwhile, you should realize there will be operational limitations and the gold will not come in the quantity it would with a dredge that has sufficient power and is not compromised in design.
Any surface dredges smaller in size to a 5-inch dredge are virtually useless, especially in Otago where there is usually some overburden to get through to get the best gold on bedrock. And for most serious dredgers even a 5-inch dredge is regarded more as a prospecting dredge rather than a dredge for production mining. And to get really serious, a dredge 6-inch and larger will be essential.
Regards,
Rob (RKC)
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Post by RKC on Nov 15, 2008 9:06:09 GMT 12
From: alluvial0 Sent: 14/10/2008 1:58 a.m.
Hi Rob,
How about running two motor/pumps in series in the above 5" situation, then you wouldnt have to alter the power jet with two inlet ports??
Alluvial
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Post by RKC on Nov 15, 2008 9:07:56 GMT 12
From: RKCNZ Sent: 14/10/2008 2:23 p.m. G'day Alluvial ( alluvial0 ), I can’t imagine how it would be of any advantage to run two motors, of equal size, in series. However … there was a dredge sold in the 80s that utilized (ripped off) an innovation fire fighters commonly employed back then which ran two motors/pumps in series. But, the motors were two different sizes, one was a large motor and the other a small motor. I can’t remember if the larger motor ran into the smaller motor or it worked the other way around (maybe someone who remembers the dredge from the 80s can inform us). It could be something worth experimenting with on an eductor dredge if the basic set up was known and if it was known what the theoretical advantages were likely to be. If I get time later today I’ll do a web search to see if I can find anything mentioned on fire-fighting related web sites. My guess would be that it could be old fire-fighting technology which has now been replaced by better technology. Also, it was only ever used on the one dredge from an obscure dredge manufacturer that has long ago gone out of business … so that tells me it could well have been just one of the many gimmicks that appeared on eductor dredges in the 80s designed by those who have never done any dredging and were just relying on gimmicks to sell a dredge to the mug-punter market. And as it did not last and was not taken up by other dredge manufactures, this indicates there were no advantages or there were even possibly disadvantages. On one of my 5-inch surface dredges I used in Otago in the 90s, I had it powered by two 5 hp Honda motors which ran two of the small Jessie pumps, and I could not have managed with using any less power. I occasionally ran it as a 4-inch dredge by running a 4 inch suction hose inside the power jet and, even then, I had minimum suction (at three quarter throttle). I was able to easily get down through about a meter deep of overburden to bedrock in shallow water, but to get through any deeper overburden I would have needed a larger dredge. Having two small motors of 5 hp on a 5-inch dredge has the significant advantage that a single motor/pump (5 hp) can be easily carried by one fit person. If the alternative is employed of using a single motor of say, 10 or 11 hp, to get the necessary minimum hp for a 5-inch surface dredge, then there is the disadvantage that the motor could only be carried by two men (except where the miner could drive right up to the water … and that does not happen very often). This photo i125.photobucket.com/albums/p71/auriferous101/b0aeb595.jpg?t=1223942501is of me with one of the old Prospectors Home dredges that ran two small motors with two Jessie pumps and because of the employment of two small motors, rather than a single 11 hp motor, the dredge was reasonably portable. This is the only photo img.photobucket.com/albums/v172/Coochee/Eductor%20dredges%20and%20equipment/dunstanOK5.jpg?t=1223942795 I could find of my 5-inch surface dredge (in the Arrow river … good gold, and there is good gold still there. I only got the easy gold from the top few feet of the overburden and had to leave most of the gold as the dredge was too small and underpowered to get to bedrock) with two 5 hp motors. Regards, Rob (RKC) |
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Post by RKC on Nov 15, 2008 9:08:32 GMT 12
From: goldtimer Sent: 17/10/2008 8:22 p.m.
Hello,
Does anybody know where I can find out the regulations on dredging in Otago rivers?
Thanks
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Post by RKC on Nov 15, 2008 9:09:50 GMT 12
From: RKCNZ Sent: 18/10/2008 11:31 a.m. G’day goldtimer , Welcome to the Gold Dredging forum! You will have to contact Crown Minerals in Wellington www.crownminerals.govt.nz/cms/minerals and a Resource Management Officer (RMO) in the Otago Regional Council. www.orc.govt.nz/Portal.asp To dredge legally you will first have to apply for a Mining Permit from Crown Minerals, and whoever you first contact in Crown Minerals will send you the forms. My suggestion would be that once you have the name of the Crown Minerals public servant that sends you the first form to fill out, that in future dealings you phone the person so the application process can be hurried along. Crown Minerals get a lot of Mining Permit applications from companies that are only paper shufflers and who are just interested in playing games on the share market, so they are usually in no rush to have their applications processed. So, if you are talking to a person over the phone you can then explain you want the claim for genuine mining and need the process carried out as quickly as possible. What size dredge you intend to use, will determine if you need to apply for a Resource Consent from the Otago Regional Council or not … if you intend to use a dredge with an intake of 6” or less you won’t need a Resource Consent. However, even if you don’t legally require a Resource Consent, my suggestion would be to still talk to a Resource management Officer to be entirely sure you will be legal and there have been no recent changes to the regulations. Also, the ORC would probably like to be in contact with you so they can be aware of what you intend and to know about the Mining Permit. It will be an unavoidable long drawn out process if you have to apply for a Resource Consent ... dredging with a 6-inch dredge will be much easier. There are different RMOs for different areas of Otago and what RMO you need to be in contact with will depend on where the river is that you will apply for a Mining Permit over. The person you first contact in the ORC will put you in contact with the appropriate RMO. Regards, Rob (RKC) |
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Post by RKC on Nov 15, 2008 9:12:35 GMT 12
From: RKCNZ Sent: 20/10/2008 1:28 p.m. G'day, I remember another photo that more clearly shows my old 5-inch dredge with two small motors ... me dredging in the Arrow river (no gold there). img.photobucket.com/albums/v172/Coochee/HOT%20LINKED%20PHOTOS/nzgoldB__012OKOKOKl.jpg?t=1224449851 With the recent rise in the gold price there has been an increased interest in gold dredging and I was thinking today that there could be a market for a small dredge (5-inch) in New Zealand, similar to my old 5-inch dredge, which would cater to those Kiwis who are starting out in dredging. No one is presently making such a dredge ... maybe someone should consider manufacturing a portable dredge to sell to those Kiwis who actually want to get some gold by dredging (even if they are still recreational) as opposed to a fossicker who is just out for a bit of fun and what ever dredge he uses, no matter how bad the dredge is, there will be little difference to the total amount of "fun" resulting. A 5-inch surface dredge powered by two 5hp or 6hp motors would keep the dredge portable and the rest is fairly straightforward (although sourcing some parts would be far from straightforward. And some parts such as suitable pumps would have to be imported). And it would be essential that such a dredge is designed by an experienced dredger or it would never be workable in real world dredging (however, most experienced dredgers are exclusively interested in dredging and my guess would be that they are not interested in using up precious dredging time designing any dredges other than their own dredges). When designing a dredge the devil is in the detail and only an experienced dredger knows the details and how to get the details correct. Looking at a Keene catalogue and then making a dredge from the photos in the catalogue is what has often occured in the past ... but the details are not known to anyone who has to copy from a catalogue and they will never come up with a dredge that can produce gold. My dredge pictured above had a significant loss of fine gold because of the way the sluice box was fed. And what this meant in real world dredging was that the water was flowing far too fast, and boiling, over the sluice box, with much of the fine gold not settling. This design fault could be simply solved if a well designed header box was used. img.photobucket.com/albums/v172/Coochee/HOT%20LINKED%20PHOTOS/abb0378eBigphotoresize.jpg?t=1224449893 Alternatively a jet flair could be used rather than a header box, however this would then have the disadvantage of making the dredge much less portable as bigger floats would be required and the dredge would need to be longer ... so a header box would be the preferred option for a portable dredge. Achieving an acceptable 90% fine gold recovery with a dredge that's designed to be portable, is difficult ... especially if the dredge is used in Otago where the abundant heavy black sands img.photobucket.com/albums/v172/Coochee/NewImageBlackSandArrow.jpg?t=1224453122will clog a sluice box with conventional hungarian riffles. However for the sake of portability some loss of gold would probably be acceptable to most beginner dredgers. The inclusion of hydraulic riffles on a dredge is the main way known to professional Kiwi dredgers to dramatically improve fine gold recovery when dredging in areas of abundant heavy black sands. However hydraulic riffles are not a practical option to use on a portable dredge as the design would be complicated and the whole dredge would have to be much bigger and heavier. Hydraulic riffles are therefore only for use on Production dredges. The usual way for a beginner to get a bad start in dredging is to purchase a dredge thats a dog. And most beginners do start with a dredge that is useless or near useless ... I did, as my first dredge was the 4-inch Goldstriker subsurface dredge. The main problem that results from buying a dredge that's a dog is that it then puts most beginners off dredging altogether ... which is unfortunate as when a well designed dredge is used nothing beats dredging as a profitable and interesting means of getting gold (especially in New Zealand which has an abundance of rich auriferous waterways). A portable 5-inch dredge such as I have described above would inevitably be priced more than what has been offered to beginner dredgers in New Zealand previously, however the difference would be that such a dredge would actually do the job. Also, there would not be a market among experienced dredgers for such a dredge, because experienced dredgers nearly always make their own dredges. And the inexperienced would probably think the dredge is overpriced and far too large as they would be comparing it with other dredges they have seen advertised. So ... it probably won't happen, and beginners will continue to throw their money away, and give up on dredging. When using a dog of a dredge beginners spend most of their time, when they should be learning how to dredge, fighting the dredge. The answer might be for someone to import quality dredge parts, such as dredge pumps, which would then allow people to put their own dredge together. Regards, Rob (RKC) |
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Post by RKC on Nov 15, 2008 9:13:52 GMT 12
From: Dredgeotago1 Sent: 21/10/2008 12:09 a.m.
Hi Rob,
Interesting comments on the 5" dredges. Your dead right about having a dog of a dredge as a first dredge putting people off. You know right away if the dredge you have brought or made is a dud. With that in mind the 4" machines i make now are all light and have quick release everything. Therefore the end user only spends 10 mins setting the dredge up at the river. and better still doesn't require a trailer to transport. If I'd have won lotto in the weekend id build a workshop exclusively for making dredges! dreams are free
When you say your 5" was loosing gold due to water flow, my way of thinking would be to make a wider sluice therefore slowing water down.....
I really enjoy designing dredges and finding ways of making them better. Lately I've been utilizing a laser cutter and getting most parts for a machine cut in batches of 3 at a time. Just thinking about a 5" dredge, a NZ made one would need to sell for about $6-7k to make it viable to make. That would be with USA pumps etc.
I'd like to take this chance to discuss Chinese vs USA pumps. I have used Chinese pumps but lately a customer demanded a Keene pump, i thought this was fair as most seasoned pro's only use USA pumps. I attached it to a 6.5hp motor and to be honest i was quite disappointed with its performance. More to the point the "bang for your buck" is far superior with Chinese pumps. A Honda motor cost $980 odd and a Keene pump about $700 total of $1680. so at $400 for a Chinese motor and pump with a 12 month warranty would that not be a such a bad thing? i can now comment on this after seeing them side by side.
If a 5" dredge requires 2x motors you'd be looking at $3400 approx just in motor and pumps. Thats more than i sell a ready to run 4" for. If one has deep pockets and want no compromise then thats fine but common sense must prevail at some point. I agree when you say that it must be affordable for the average person.
Thats all for now
Cheers
Dan
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Post by RKC on Nov 15, 2008 9:15:15 GMT 12
From: RKCNZ Sent: 21/10/2008 8:44 p.m.
G'day Dan (Dredgeotago1),
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 emphasise, 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.
Regards,
Rob (RKC)
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Post by RKC on Nov 15, 2008 9:15:51 GMT 12
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Post by RKC on Nov 15, 2008 9:16:49 GMT 12
From: Dredgeotago1 Sent: 21/10/2008 9:50 p.m. Hi Rob, The Chinese must have literally pulled a Honda motor apart and copied them bolt for bolt! I'm told you can actually use Honda parts as spares...... Just for peoples interest, stats on volume and pressures as follows: Keene P180 = 1155 litres per min and max head pressure of 49m Chinese 3" = 1000 litres per min and max head pressure of 31m The key for getting pressure is the reduction from 3" to 7/8" To get an idea of the pressure check this link: thedjdan.googlepages.com/venturiCheers |
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Post by RKC on Nov 15, 2008 9:21:48 GMT 12
From: RKCNZ Sent: 23/10/2008 6:21 p.m. G'day Dan (Dredgeotago1 ), By making the diameter of the venturie intake (not too sure of the exact terminology to use, but most readers will probably understand), only 7/8", you have made a critical mistake. With this design fault its no surprise to me that you have been unable to make a critical evaluation of what pumps would be best for your dredge. The intake diameter of 7/8" is far too small! The tube diameter should be twice, or more, the diameter you decided to go with. This suction nozzle img.photobucket.com/albums/v172/Coochee/HOT%20LINKED%20PHOTOS/P1010001_3inchA-1.jpg?t=1224732698 illustrates how large the diameter should be on a venturie in relation to the diameter of the jet tube. Only a large diameter venturie intake can get the most out of a dredge pump so the dredge has enough suction to work with. If I had the time I could do some research on the Internet about venturies and give a technical explanation of why its a mistake ... but I won't, unless it starts raining. I do however need to at least point out the mistake so any other members who are building their own dredges can be aware of a problem that would be costly to rectify. Its a mistake that's probably been made by numerous dredgers when building their first dredge. And I know what a costly mistake it can be as I made the same mistake myself when I built my first Production Dredge many years ago. What I find a little perplexing is that you should have become aware of the mistake during the "sea trials" of your dredge. My guess would be that the problem was not as immediately apparent as it should be because you were using an unsuitable pump that is only designed for moving water in volume. You could 'not' have tried a dredge pump during the "sea trials" as it would have then been obvious as a problem and the venturie needed redesigning. During the "sea trials" you should have carried out some experimenting ... such as putting a dredge pump (a Keene pump for example) on your 4-inch dredge that has the narrow venturie. It would have then been noticeable that there would be little suction produced at the nozzle. However ... the fault is 'not' the pump being used. The fault is using a badly designed venturie. Another experiment that should have been conducted would have been to replace the venturie so the intake is increased to about ... say, 2" in diameter. And by using a dredge pump, you would have experienced a dramatic increase in suction at the nozzle. The dredge pump would have then been working as it was designed to work by moving water at a high volume combined with high pressure. Now, if you used your Chinese pump, on the 4-inch with a large diameter venturie installed, my guess is that you would be lucky to get any suction at the dredge nozzle (but you have probably already found this out for yourself). The pump would be delivering water in a large volume, as its designed to, but without sufficient pressure to introduce water in volume into the power jet ... at pressure! My guess would be that you have learnt from what experimenting you have done that the only means of getting some "punch" out of the Chinese pump was to reduce the venturie to a small diameter. 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. When I built my first Production Dredge it was built in Sydney and had its "sea trials" in a farm-dam just outside of Sydney. I then drove img.photobucket.com/albums/v172/Coochee/ToEdit2005_050.jpg?t=1224731339 with it all the way to North Queensland where I went on to a farm img.photobucket.com/albums/v172/Coochee/P3300006.jpg?t=1224731166 that was the closest the road went to the gold field I wanted to get into (I was staying on a farm owned by another dredger who let me stay in a hut img.photobucket.com/albums/v172/Coochee/qldandnz024b.jpg?t=1224731677 on his property rent free on the agreement that I stay out of the river he was dredging). Anyway, I then spent about a week carrying in the dredge parts myself through rain-forest to the stream I wanted to dredge (carrying each 10 hp motor on my back). And when the day came to start dredging img.photobucket.com/albums/v172/Coochee/qldandnz016d.jpg?t=1224731537 I fired up the motors and got on the nozzle. And I immediately realized I did not have anywhere near enough suction. So, on getting back to the farm and telling my dredger friend I had no suction, he told me the diameter of the venturies (there were two) were too small and that was why I was not getting enough suction. He also added that he had noticed the mistake when I had arrived and unpacked the dredge ... but he did not want to say anything at the time ( probably out of politeness). Once it was pointed out to me, the mistake was obvious. And now that I knew what the problem was I went back down to the dredge and carried out the power jet. The venturies on the power jet were then replaced by bigger diameter venturies at a sheet metal shop and I had the replacement power jet back on the dredge in a few days. And when I commenced dredging there was all the suction I needed. No gold however in that spot, and I had to drag the dredge out (uphill this time). Later I put the dredge into a stream a few minutes walk from the hut I was living in img.photobucket.com/albums/v172/Coochee/qldandnz026d.jpg?t=1224731611and I spent a few months on reasonable gold with a dredge that had good suction. Regards, Rob (RKC) |
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Post by RKC on Nov 15, 2008 9:23:08 GMT 12
From: Dredgeotago1 Sent: 23/10/2008 10:21 p.m. Hi Rob I have done my fair share of testing and around that time I talked to a few die hard gold miners I know (Keith McNaught & Barry Clearwater) who have one thing in common, they say 7/8" jet ID is the magic number. The picture you linked to of a black coloured 3" suction nozzle, i doubt they would run the same diameter all the way from the pump right into the main line as the friction losses would be inefficient. If you look closely at the picture you posted, the tube bend is cut and joined. Why did they not carry on the tube and put one mitre cut and weld it to the main line? I'd say there is a machined reducer there. Id like to back that up with an experience i had with my friends 6" dredge. We were discussing venturis at the time, his suction nozzle looked similar to the one pictured except for diameter. He told me to reach up inside the 6" line and put my finger in the jet (that appeared 2") so i did and my finger hardly fitted in the jet. It would have been very close to 7/8" This dredge by the way way dangerous to stand behind when running. There were certainly no vacuum issues. Go to this link: home.earthlink.net/~mmc1919/venturi.htmlI haven't got time to go into this but its in the realms of Bernoulli's principal. To get water moving at speed in the main line you need to get the jetting water to a fair velocity first. The dredges seen on Trademe in New Zealand have the option of Keene pumps and Honda motors. They are more setup for the hobby miner who doesn't have a spare $7k under his mattress What diameter was that dredge that needed 2x 10hp motors? Cheers Dan Cheers |
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Post by RKC on Nov 15, 2008 9:24:23 GMT 12
From: VJG73 Sent: 23/10/2008 11:10 p.m.
Hey
Though I would throw my 10 cents worth is. Basically there are two options I have found for getting a venturi to work properly. Either way will work if matched to the right pump. High pressure pumps through a 7 / 8 nozzle are very effective for deep water dredging. I have a couple of P180s on Honda's which I have spent ages with getting them to optimum efficiency. I have tried everything from 2 inch right down to 5/8 nozzles at 11 degree entry. The most important point is to reduce frictional loss before being reduced down.
High Volume Pumps such as my Keene P1500 work better through larger venturi nozzles. Twin 2 inch entries on a 8 in jet work well with a great balance between pressure and volume.
You should also not that the use of eccentric reducers rather than concentric reducers on the suction side creates less frictional loss and turbulence. This inturn can increase efficiency on the pump suction side.
Well told you it was only worth 10 cents..
Cheers
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Post by RKC on Nov 15, 2008 9:25:20 GMT 12
From: Dredgeotago1 Sent: 24/10/2008 12:00 a.m.
That was worth 20c
I forgot to add that note you said about 11 deg, your bang on the money there.
I had pondered what was better out of eccentric and concentric reducers. I had used eccentric as i was tight for room. Now i use concentric but after your comments i will research it and might swap back
Rob, In summary my pump evaluation was fair as the venturis were identical in both dredges. I will say though that yes, it it a compromise in design to use a Chinese pump. They still do the job well enough for a beginner however.
Cheers
Dan
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