Collaboration How to run a quieter/silent dredge p

[RKC]

From: Pascal__Fortier (Original Message) Sent: 2/07/2008 9:38 a.m.

Hi, this is Pascal I thought we could start a Collaboration to exchange knowledge to how to run a more quieter dredge in a environmental friendly way. I do not know a lot of ways. Do you? Share your knowledge! I am going to start this discussion on 6 dredge forums that I go on. The links will be provided in my next post to direct you directly to the post you are interested in.

: 1 OK here a simple way I know tight all bolts and reduce vibration everywhere you make sure no bolts are missing a piece of rubber under a compressor goes a long way.

Thanks

Pascal Fortier

[RKC]

cancellation Sent: 3/07/2008 6:01 p.m.

G’day Pascal (Pascal__Fortier ),

Reducing the noise emanating from a dredge is certainly something worthwhile considering and I can think of a number of good reasons to reduce the noise from my dredge. (BTW: there can even be a good reason to take a muffler ‘off’ a dredge motor. For example, I took the muffler off one of my dredges when I was once dredging in very remote country. I was dredging at a high altitude in the Otago high-country, and the extra power I got from the motor, with the muffler removed, made it well worth doing. The noise was incredibly loud in the air and unbearable when I was above water and near the dredge, but it didn’t trouble me in the least when I was working as the noise was so cushioned by the water I could barely hear it underwater.)

The standard mufflers that come with stationary engines are essentially a compromise between reducing noise and allowing the free flow of the exhaust from the piston. And in this respect its probably simple enough to reduce the noise emanation from a dredge by just adding a bigger muffler … however, the result would be unacceptable to most dredgers in that the power output of the motor would then be reduced. So … the option of using a bigger muffler is not usually attempted.

If a dredge engine is run at high revs compared to being run at half throttle, the difference in the noise level is quite dramatic. Therefore, reducing the revs is the simplest means of reducing the noise level. However, if any of the engines typically found on most recreational dredges were run at half throttle the result would be very little, or no suction at the nozzle. Recreational dredges are design compromises and the compromise with recreational dredge motors is that the size of the motor chosen is the smallest size possible. And to get any suction at all, these engines have to be run at a high rpm … and running at a high rpm is noisy! Therefore attempting to reduce the noise on a recreational dredge is a difficult proposition.

One way often proposed to reduce noise levels on recreational dredges is to run the exhaust below water level. I once tried this on the first dredge I ever had, but it did not work. There was a back pressure that caused the engine to stop, and that was the first and last time I tried that theory.

Production dredges can be easier to run quieter as the engines used on production dredges are usually much larger than the engines used on recreational dredges, and can therefore be run at reduced revs without sacrificing suction.

The quietest production dredge I’ve ever seen was a dredge owned by Lubo, that he used in Victoria during the 80s. img.photobucket.com/albums/v172/Coochee/Eductor%20dredges%20and%20equipment/nzgoldA_016.jpg?t=1215051097
When it was running you would have to get within less than 10 meters of it before the motors could be even slightly heard (even on a still day with no wind). At the time I didn’t realise why it was so quiet, but I worked out later that what was most likely occurring was “noise canceling” (aka phase cancellation).

There were two large motors on his dredge (it was one of the old Keene single sluice 8” dredges) and he used to say he tuned each engine so each ran out of phase with the other. I’m probably not explaining it very well and I can’t remember ‘exactly’ what Lubo said he was doing. However … I now realize what was occurring was most likely “phase cancellation”. That is, the noise from one engine was cancelling out the noise from the other engine.

Wikipedia at en.wikipedia.org/wiki/Active_noise_control
says about noise canceling, “Sound is a pressure wave, which consists of a compression phase and a rarefaction phase. A noise-cancellation speaker emits a sound wave with the same amplitude and the opposite polarity (in anti phase) to the original sound. The waves combine to form a new wave, in a process called interference, and effectively cancel each other out - an effect which is called phase cancellation. Depending on the circumstances and the method used, the resulting sound wave may be so faint as to be inaudible to human ears”.

This web site gives a good explanation of “phase cancellation”.
www.thevettedoctors.com/corsa_rsc.htm

Regards,
Rob (RKC)

[RKC]

From: Pascal__Fortier Sent: 5/07/2008 5:25 p.m.

G'day Rob!

Thanks Rob for the long post.

From the Alaska prospecting forum sent me this link. www.jackssmallengines.com/strapmain.cfm
It's seem to be as you were writing, I do not think it would drawn any power but I will get in touch with the manufacturers.

I am presently looking for my exploration dredge, I have many different streams to explore in far country so a small dredge is a must with some modifications you understand. The big dredge is waiting.after the little one to finish everything. Water is not so far away from dry-suit temperature.

One way often proposed to reduce noise levels on recreational dredges is to run the exhaust below water level. I once tried this on the first dredge I ever had, but it did not work. There was a back pressure that caused the engine to stop, and that was the first and last time I tried that theory.

One big dredging player told me that he had problems because the CO2 would cause bubbles to form in the water and then bust near by the dredge forming a cloud of CO2 and some bad mind altering gases. (unless you bring along a long tube to direct them away) But I do not really like the idea of having a system introducing the gases directly into the stream.

It is a wise trick that Lubo had. You can be sure I pressed save this page and Hop into the Mining File.

Regards
Pascal Fortier