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Dredge flow/pressure for suction nozzle


Gidday bit of a question for the guru’s. At what point. Does pressure and volume cross over for a 6” dredge.
Is there a calc or a way to figure out how to get the correct volume/pressure ratio sorted. Just about to have a 6” suction nozzle built/ modified. And need to sort the jet sizes. Will be twin jets into it.
Has to push material about 3m. An no I don’t want to run a jet log. As it’s nit practical for my setup.
Any info would be good thanks


Pressure and volume are important no matter what dredge you have!. The key to a good performing dredge is having a good dredge pump that has a mixture of pressure and volume. By far the best solution for this is a centrifugal pump with a closed impeller design. The pump is probably the most important design consideration on a dredge!

You talk about a suction nozzle setup ( you say you dont want a jet log) with a twin log setup?. I’ve never heard of this type of setup on a suction nozzle and can tell you you will need 3 hoses to wrestle with 1 being the suction nozzle and x 2 high pressure lines to the jets. This is just plain impractical! a 6 inch dredge hose is a monster to handle on a good day bloody hell having to man handle it via a suction nozzle setup! There is a reason none of the major dredge manufactures made a 6 inch suction nozzle and this is why. The biggest you could get was a 5 inch.

Im guessing you want a suction nozzle as you will be using this out of the water?

To answer your question and perhaps steer you in the right direction you need to provide some more info such as the pump output and hp as well as the pump outlet diameter size. Also you will need to stipulate what the design of the reducer is within the jet?

Generally the formula is you divide your suction hose diameter by 4.5- 5,25 to get the “jet size” this would be dependent on running intake pressure at around 30-35 psi and having a pump capable of moving minimum around 2200 liters per minute. This formula assumes you have made a reducing conical jet. A conical reducing jet allows the water entering the suction nozzle to have the required velocity or pressure to induce a suction effect. A well designed jet should always be built around the pump that is powering it and is probably the second most important thing on a dredge behind the pump.



I already have a 6” nozzle 2” feed line that splits into 2 jets just as it turns 180degrees to to into the nozzle. I will be replicating this but on a swivel nozzle. Its on a submersible dredge and i was hoping to get away with running it on a proline hp400 on either a 6.5 or 8hp motor. Will tickle it up a bit to get a bit more out of it if i have to but at the same time don’t want to make it un reliable. image|566x500


A 6.5hp should be fine with a proline hp400 pump. There very good pumps. The 6.5hp do struggle a bit if you are running a 2 piston compressor like a Ghast or PCA with that pump especially if your at altitude and/or its a hot day but there’s lots of things you can do to ekk out a bit more performance out of them. Start with removing restrictive exhuast and inlet and replace with free flowing velocity stack and go cart exhuast once you do that replace main jet to a .88 and straight away you have an 8hp motor ! I’m assuming your running a Honda gx200 not a clone gx200?

I run 15hp pumps on my honda gx200 motors piece of piss and also managed to make them lighter with a lot of billet parts.

With that pump combo if you can design it so you can interchange out the reducers to get you the most sux would be the best bet. I’d be starting with a 1 inch and playing round either side of that to hone in on the sweet spot. The hp400 has a far bit of volume behind her but lacks pressure at higher rpm.
I wouldn’t be going down the route of splitting the jets into 2. Keep it simple. I just don’t see the logic of that on a suction nozzle setup. Reason being is you want your jet of water to enter right bang in the middle of the suction nozzle. This helps increase efficiency and ensures the high pressure jet of water remains in the thalweg of the water column. By splitting your actually off-setting the jet column and introducing considerable turbulence into your suction nozzle which will reduce effeciencey.