6 inch dredge not sucking like it should

[timsuss103]

Hi,
I have recently bought a dredge down here in honduras, it's homemade, using a power jet 13hp Honda and a Venturi pump that was designed by a company down here.. I have been using it for a number of days with great suction. It was really sucking. I turned it off for lunch and when I came back to fire her up, the suction was greatly deminished. Like half power. I checked for clogs and everything was clear. There is water running through the sluice coming from the pump. But the suction end is not sucking like it was sand build up in the hose while sucking. I'm wondering if you all may have some brilliant test I can use to determine what the problem is.. or some helpful things to check. I'm new to dredging and have been going through quite a steep learning curve, especially since all the connections are sealed with nothing more than tire tubes wrapped tightly.
There is a small leak coming from the pump, but it has been there the whole time.
Does it matter how high the the connection for the water coming from the pump is, in relation to the pump?
Anyways figured you bright minds with experience might be able to help this poor greeny.
Thanks!

 

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[smokeythecat]

My first guess would be a blockage. The one and only time I dredged, it was a blockage every time it slowed. Most times the blockage was in the hose.

 

[dredgernaut]

foot valve plugged? I always get plant material stuck to my foot valve, stops the correct amount of water from being pulled in

 

[Goldwasher]

organics in the pump itself? stuff that made it past the foot valve.? Remove the housing and check the impeller.

leaks in the hose are never good. a new one can really affect suction.

is the venturi at or below the surface of the water a slight change can make a big difference.

double check for clog in the hose some times its hard to see a thin rock stuck sideways right at the venturi (jet log)

a small rock in the jet can happen too

 

[russau]

I agree with Goldwaher on the venture's location being raised higher to the surface ! Before anything , check to make sure the venture is under water or it'll NEVER suck for you!. Another item to check is the flapper on the foot valve....If it was stored improperly and not hanging up-n-down Or having the rubber flapper open while not in use , it'll warp open and leak your primed water and this also could be your problem. Good Luck on your search !

 

[timsuss103]

Wow you guys are a big help. It was a thin rock near the jet log. But now I am curious, hoping I am using these terms correctly. Is the jet log the point where the hose that comes from the pump meets the jet? If so I have had this thing set up wrong the hole time. My jet log has been about a foot out of the water. That's must be why I have to pump the suction hose up and down and quickly put it in the water to get suction. Ah the internet and your great minds, what a blessing ��.

 

[russau]

Yes the jet log (venture) needs tobe kept under water for suction at the nozzle and it appears your foot valve (rubber flapper) is leaking. Take it apart and flip the rubber flapper over and that should fix your leaking foot valve problem. Let us know how your doing and send some pics. Good Luck!!

 

[Goldwasher]

The jet log is the whole thing the metal tube with the angled jet. The venturi is the more specific area where they meet and the physics do what they do.

when it is at the hose by the box it is called a Jet Log. when it is at the suction end of the hose it is called a Suction Nozzle" They both have a venturi

https://en.wikipedia.org/wiki/Venturi_effect

Based on your description I figured it was an obstruction somewhere on the pressure side.

Yes get the jet log at least at the waters surface with the venturi under water. If you had decent suction before you should have much more after the change.

A 13hp with a good jet and pump should have some great suction.

 

[Darth Placer]

I had a problem once with sudden loss of suction. It happened on a twin jet log. The two inlet pipes make a 180 degree transition. As it turned out a rock got into my hose when I was putting it together or the last time I took it all apart and jammed one of the inlet ports. A quick bang with a dead blow hammer and spinning the jet around freed the little stone.

Lost a lot of hours on that one... live an learn.

For the most part jams will almost always be at either a sharp bend in the suction hose or at the point where the hose meets the jet log. They tend to get caught on the sharp edge of the log.

 

[Hoser John]

To dredge is to learn as always something new happens-some good-some bad but always a lesson-John

 

[mendoAu]

Time for a quick tip. You know how you sometimes don't realize a plug in mid section of your hose until you've sucked up a couple more feet of gravel. Make life easier, end for end your hose. You can then suck all that gravel out and usually get lucky with that stuck rock falling back out the direction it came from.

 

[timsuss103]

You guys are great. Really appreciate the insight here. I've got some more questions.
Ive arrived at a later of hardpack that doesn't budge with my bar. I've seen on other dredges a high pressure water line that people use to spray the hardpack under water and suck simultaneously. How would I go about setting up one of those? Do I need a second motor and water lines and pressure nozzle? Also the creek I'm in is fairly shallow, however upstream has some pools sitting after a waterfall that haven't been touched. Thinking an air compressor would be the ticket here.
Being in Honduras dredging specific equipment is hard to comeby. Could I use an aircompressor from a car? Attach a line and suck air from the line when I need it?

 

[N-Lionberger]

You can put a pipe T or Y if one is available onto the pump, run a 1" hose to a ball valve with a hose barb for a nozzle. If you can get the dredge lower in the water you will have a lot more suction power.

 

[russau]

I agree and it's called a blaster nozzle! Best idea to use one when dredging!

 

[njcommercialdiver]

i had a long thin rock cause a jam in my dredge this year in north carolina, it jammed just in front of the jet tube, i ran the jam rod thru it a couple times but it didnt hit it, i saw it after i shut down and visibly checked the tube and hose for obstructions. i think iot turned sideways when the flow was running thru the hose and when i would run the jam rod, it would turn skinny ways

 

[mendoAu]

Them dang pesty rocks...I call the long thin ones "tumblers" cause that's just what they do.
About that blaster setup (got one and they work big time) if you could post a picture of your pump we might be able to guide you thru the setup.

 

[Goldwasher]

You guys are great. Really appreciate the insight here. I've got some more questions.
Ive arrived at a later of hardpack that doesn't budge with my bar. I've seen on other dredges a high pressure water line that people use to spray the hardpack under water and suck simultaneously. How would I go about setting up one of those? Do I need a second motor and water lines and pressure nozzle? Also the creek I'm in is fairly shallow, however upstream has some pools sitting after a waterfall that haven't been touched. Thinking an air compressor would be the ticket here.
Being in Honduras dredging specific equipment is hard to comeby. Could I use an aircompressor from a car? Attach a line and suck air from the line when I need it?

Yay a picture!!!

See where the green hose meets the jet. You really want to get that lower. maybe move the whole sluice forward? Fashion a frame that lowers the box closer to the water.

I think that is the first welded steel crash box I have ever seen lol.

i do not envy the fact that all your connections are wrapped. Vs. hose clamps... that has got to be a major pain.

But good job making it happen keep it up!!

 

[seafox]

Different situation but we used to flood irrigate and had one pipe that started out as an 8-inch and went down to a 6 in and 1 time got a blockage in it when a piece of grass had a plastic bag wrap around it and it would I mean it wasn't across the whole pipe it was just like a lion and the the friction just killed the flow

 

[logjam]

As far as using an air compressor from a car to breath from, that is probably not a good idea.
You are setting yourself up for illness or death if you breath air from a compressor that uses oil for lubrication of the compressor cylinder. You need to pay attention to the quality of the air you breath. Try to use components that are designed for breathing., and pay attention to where the air is coming from.. .you dont want to be breathing the exhaust from your honda.

 

[njcommercialdiver]

logjam, that is not correct if you are refering to a tire inflating/air nailer type compressor, it is if the OP means an A/C compressor from a car
90 plus percent of commercial diving air compressors are splash lubricated air compressors because diaphram compressors dont provide enough CFM (a kirby morgan helmet requires 5 cfm at 90psi to work "correctly"), they use a synthetic oil (to not combust when hot and cause the offgasses you are talking about if using just straight hydrocarbon based oils), then they are plumbed into a volume tank to capture any oil splash over, then run thru a double canister filter ( first one is a fiber , second is a carbon/fiber hybred) to remove anything else and any foul taste from the volume tank. this is basic knowledge taught in many dive schools. you also use a remote air intake if the wind direction isnt toward the intake and away from the exhaust

you can take a new wheel barrel air compressor drain the hydrocarbon based oil and put the synthetic oil in (several companys make them, i use Bauer in all mine) , run it for abt half an hour , then when its nice , hot and mixed, then drain it to remove all traces of "hydrocarbon" based oils, then fill with synthetic oil and add the filtration and you are good to go. there are several commercial diving equipment companys in the "gulf" area from new iberia along the panhandle in "oil patch" territory that will sell it to you or marvel in camden NJ but they tend to not deal with anybody not Commercial dive affiliated