Pump for 2 inch dredge

I also use a WX10 for my 2" dredge, However, I use it with a special 4 jet venturi designed for the limited volume of the pump to still reach 30psi and draw 80gpm while using only 20gpm. A wx10 with a standard off the shelf suction nozzle or log jet would be substantially underpowered. A infinity/couple jet would also work with it. AP are you using a special jet? A off the shelf wx15 will get ok suction with a 2", but the Honda with a HP pump will really do the job and more. The thing to keep in mind is that a standard suction nozzle or log jet have close to a 1-1 ratio of draw gpm vs jet gpm. To get 70gpm suction draw, you need close to 70gpm supplied to the jet at pressure. If you are looking at other pumps, you want to look at pump curves and find a pump that can deliver 60-70gpm @30psi to even get close to the range that the small Honda with the HP pump can do.

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With all due respect to artisi this isn't quite true (it's a bigger pipe), but more of that later.

first off some assumptions needed to make the calculation work:

Flowrate / velocity. From a quick search it looks like you need about 5m/sec min in order for the gravel / cobbles to be lifted up the pipe and maybe a bit more so lets go for 6m/sec.

17" ID this works out at m3/hr
The differential head of the pump is likely to be with approx. 3m head (absolute) on the suction side to (10m + 5m lift from pump + 2m friction loss) so say 15m differential head.

That pump looks pretty basic to me so if we take an efficiency of 0.5 we're being generous.

fluid density - assuming we have material with an SG of say 1.9 and we have it in a volume ratio of 20% in water, this makes the average fluid density SG of 1.18

shaft power of the pump is then Q x m x SG / 367 x eff in kW
power is 303kw = 405 hp

However there is a lot of uncertainty here so I would go for at least 500hp shaft output.
Remember the pump will only take the power it needs so using a larger engine doesn't mean a bigger fuel bill for the same duty.

HOWEVER, I'm not sure you fully appreciate the impact of extra depth.
For a pump mounted at river level, the only driving force you have to flow water up your 30m long tube is atmospheric pressure minus the pressure at the pump inlet. Whilst the theoretical limit is 10m head water, the practical limit before the pump starts to cavitate and loose suction is probably about 6-7m "lift" capacity.

for a 30m long tube running at 6m/sec you will probably loose 2m at least in friction losses so that leaves 5m head. That 5m is required to lift the heavier fluid up the pipe. That 5m is the same whether you have a tube 10m long or 30m long.

So what changes? - the percent of gravel / rocks you can lift in the water. So the deeper you go the more water per tonne of gravel you need to move which hence costs more and more per tonne of gravel as you go deeper.

A fairly quick search on the internet shows that for a surface mounted pump you are generally limited to around 20-25m max in suction lift before it either doesn't work (not enough velocity or the pump simply cavitates or just becomes very expensive. For 30m + you either need a submersible pump or accept that your percent of material is going to be as low as 5%. Many dredgers locate their pump inside the hull at the bottom and have deep dredgers of >5m water depth to help the pump.

However if you want to give it a try that's up to you - just don't blame the pump when it doesn't do what you want it to do.

Speed of the pump? No idea but I would start at rpm and wouldn't go much above .
NOTE: without doing some tests on the pump to establish your pump curve, the pump might want to consume more power than your engine can supply.
Flow is proportional to speed and is a minimum of about m3/hr
Head is proportional to the square of the speed
Power is proportional to the cube of the speed

Hence you might find yourself trying to increase speed to get the flow rate / velocity you need but then running out of power. The only answer then is to modify the impellor by making it smaller diameter or use a smaller pipe.

Good luck and let us know how it goes.



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