New Zealand Gold Prospecting & Metal Detecting Forums Archive

I've decided to give the gravity suction dredge a go.
After ringing round a few local plumbing supply shops i got hold of a 30 metre roll of 4 inch nova flo, the type that isn't perforated of course.
Man, this stuff isn't cheap. prices varied from $125 inc to $255 plus gst.
Basically the length of nova flo is all thats needed. i think i might still place my sluicebox at the end of it just to check whether the nova flo loses any gold. i 'm planning on making up gib bucket to take the water before it enters the sluice, so as to slow it down if it has too much force. i might add a 2 inch dredge jet to the top end to make a venturi effect.

what my current problem is is that i need to find something simple as a reducer. someone suggested if you don't have one just to use your hand as a guard against larger rocks going up the hose. i think bugger that, too much hassle. i don't want to have to hold my hand over it all day. so i need some sort of reducer in the meantime before i upgrade to a powerjet nozzle.

i saw online on a u tube clip the guys rammed what looked like a pvc plumbing fitting up the nova flo to reduce its intake diameter (the last thing i want is big rock blockages).

well, it seems the local plumbing shops don't have anything if this diameter to fit inside the nova flo - most fittings are designed to go on the outside of pipes.

so i'm looking for suggestions. the simpler the better. i don't really want to have to cut the nova flo itself on the end to reduce it that way.

i will also need to figure out a way to attach a standard dredge suction jet.

any ideas?

Well, a couple of weeks back i got the help of a mate and headed out to test this gravity dredge.

all it was was a 30 metre length of novaflo, the type with no perforations.

it took awhile to figure out a cheap and easy means to fit some type of reducer at the top end.

i settled on a plastic concrete chair that i had in my shed. these are about 40 cents each and are used in the construction industry to hold reinforcing mesh up while a concrete floor is poured.

i attached it to the top of the pipe by drilling 4 holes in the novaflo and wiring tightly in place with some reinforcing mesh ties which i also had in the shed.

i cut off the top part of the mesh seat so all the was left was the bottom plastic rim. perfect.

my mate later suggested that i should have left the whole thing intact but i think it would have left too small an opening.

after a bit of pissing round we found that it was next to impossible to get all the trapped air pockets out.

the stream was raging and every time we got one section of the pipe sorted it would screw up further along.

it actually would lift off the stream bed even with heavy rocks weighing it down.

eventually my mate hauled half the novaflo up the very steep stream bank.

we filled the remaining half and then let down the half that was up the bank.

this method worked perfect and was so simple.

once it was running it did have good suction but i think it needed more.

i am now going to reduce the intake end.

i have bought some pvc plumbing parts to reduce the opening from the 4 inch novaflo down to about 2 inches so that i can also attach some flexible hose.

we found that the novaflo was near impossible to move once it was full with water so not too good for manouvering around the riverbed suctioning.

all in all the gravity dredge is a cumbersome contraption. perfect if you can leave it somewhere. not so good if you have to haul it out each time. definitely a 2 man job.

will still look at getting a 2 inch keene backpack dredge that converts to a highbanker i think.