A different gravity dredge power jet question.

[OwenT]

So this other gravity dredge thread here got me thinking. I didn't read it too well but as far as I saw it didn't cover what I'm thinking. So the question is can you get venturi suction using pipe running down a steeper portion of creek? See illustration:

 

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[rivets]

"I didn't read it too well but as far as I saw it didn't cover what I'm thinking"


Had you read it ......... you would have seen .... that it covered your thoughts very well


PS: your illustration sucks ... or rather ... it won't suck

 

[Timberdoodle]

Hi Owen, Good question. There are basically 2 ways to run a gravity system. The first is a siphon type system where the sluice is located around 4-5ft in water elevation down stream of the suction line. Sometimes you can do this with 20ft of hose and sometimes you may need 100ft of hose to get the drop necessary. The second way is to use a jet connected to a hose running uphill in elevation to provide the head pressure to run a standard jet to create suction. This usually requires 70-100ft of elevation difference to supply the same pressure a pump will deliver to a jet. Your drawing represents the second type and yes it can be done but it does require some understanding of hose/pipe sizes to do this effectively. In the other thread we are discussing whether combining both methods may generate enough additional suction in a siphon system in areas where you can't get 4-5ft of elevation difference and whether a modified jet system used with lower head pressure may help provide some additional suction. The jury is still out on this one as to how much head is needed with a specific jet designed for this purpose. Hope this helps

 

[mike(swWash)]

Here's the feet of head (height of inlet above outlet) calculation....1 foot of head = 0.4335 pounds/square inch. So using this conversion you'll need 69 feet of head to achieve 30 psi outlet pressure. Doable, but probably only if you have a waterfall nearby or feeder stream far above in elevation that you can pipe the pressurized jet water from.

As said above with the type of system in your drawing, how much pressure and flow you need to achieve suction for a dredge is the same whether using gravity or pump supplied pressure and will also depend on the suction hose size and the depth you plan to dredge from also the jet ventury type you choose.
I believe the efficiency of suction to x type jet pressure goes something like this, lowest to highest is a standard suction nozzle with pressure jet at inlet, then the standard jet log, better is a couple jet type system and most efficient is the infinity type.

2 websites I use to answer questions for myself on these type of ideas.

Online Conversion - Pressure Conversion


Calculator: Water Flow Rate through an Orifice | TLV

 

[OwenT]

Thanks, sounds like more work than it's probably worth but that's cool to know it can work.