This topic is something that I am still doing some research about. Depending on the size and length of your suction hose, what size motor for your pump is best and how much pressure should it have? For example a 5 inch suction hose should work best with a 6 or 7 hp engine?
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Orrin, that is very good explanation of the subject of pressure vs volume in the dredge/HB working requirements .
Doc has put it in plain language anyone can understand.
Thanks for the link, Orrin.
Now Reed has nailed it right in the head.
What I understand that if the sluice is not higher above the water and you're running a short hose , you''ll get by with a lower HP engine, things start to change if your sluice is stood higher and the hose is runs longer then you need much bigger HP engine/pump combo.
Ahmed, I am by now means an expert in pumps and pump technology and have been searching to answer my own issues with using the dredge option on my highbanker. I believe what the Doc was referring to in his article is the issue between flow (GPM or GPH) vs. the head pressure or lift of the pump being used. Most trash pumps have very high flow rates but have limited Head PSI or lift. Most dredge pumps are generally higher quality with much greater lift or head pressures.
It turns out that a high pressure pump can be more effective achieving the lift required for a land dredge with the same or less water flow. The size of the motor is determined by the pump characteristics and shaft sizes.
I found this link that may be helpful to you and others to understand these functions of the pump. http://www.onestopfire.com/head.htm Article is titled "Lift, Head & Flow" and has some interesting conversion charts that may be helpful in determining the type of pump required for your application.
Rob,If i comment and then Reed comments,please disregard my comments and listen to Reed. hahahaha! He knows more than I will in 2 lifetimes. Best of luck Rob!
Naw, you gave him a good answer Ryan but not knowing anything about the dredge he is configuring add's a bit more to it. If he has a new style low profile 5" Keene with a powerjet then the 8hp is a good motor for a 15ft hose and that low profile dredge with a single stage box. Now-a-day's with Keene's 3 stage even they start with a 10hp motor as their smallest. On the old triple side by sides it took an 8hp motor to run a 4" with good suction because they stand higher out of the water and the header box has the powerjet at a steeper angle that requires a lot more power. Dual 8hp motors on the old 5" triple was a great combo but many came with twin 5hp motors. Heck... the more suction, the less plug ups so I run a 9hp Proline HP500 maxed out on my 4" and it's a dredge to be reconned with for sure :)
It also depends on the width of your box and type of jet. To answer the "should work best question", neither a 6 or 7 is best. Best would be a 24"wide box with 18hp electric start Briggs coupled to a Keene P350. But twin 6.5's with P180's or HP350's are a great option for lighter weight maneuverability. With the 18 you can run a 1¼" fire hose for a blaster and that is the real deal.
Dredging 8- 26-2006 008.jpg
I'd throw an 8hp Honda on a 5".Especially if its got a 20 foot hose on it and you plan on dredging at any sort of depth. Ya it weights 55 pounds but you dont want to be in a position where you dont have enough power. Also it would depend on the box style you are using. For instance a straight,regular style box can get away with a bit less water than say the over under box or the triple box. But in my opinion,I wouldnt put any less than an 8 hp on it.The next size up dredge a 6",either comes with 2x 6.5 hp's or 2x,8's hp. This is just my opinion based on my experience. Hope it helps!
Rob, I had similar issues, got this from the Doc at Gold Hog, might help you out.
http://goldprospectingforum.com/viewtopic.php?f=28&t=1296