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plastic bag evacuator

by kakiemon May 11, 2019
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Very nice! I'm curious about how you picked the dimensions/angles? Guess and Golly, Calculations, or CFD? Myself I do a lot of by guess and golly, but I'm always curious about CFD results.

Got me ! Yes I just guessed the dimensions and shapes. However, I looked through different nozzle designs and tried to get an idea about the optimal shape. Perhaps I should have used some free CFD Software. For now I tried to show the idea to use a venturi to evacuate bags in a simple way.

Nothing wrong with starting by G&G, it's often gets me a workable result. CFD sounds dreamy, but I've yet to see a package that's really user friendly. I'd imagine that the major variables are port diameters, and so if someone wanted to tune this, they could redraw it with exchangeable inserts for the bag air out and blown air out nozzles.

I'm curious about this because I've been trying to think of a simple system/mechanism for pumping a small amount of water from a low speed high flow creek. I've been wondering if a venturi vacuum powered ram pump could be built, maybe even using a Tesla valve, so it would have no moving parts and be completely 3D printable. I just don't have time these days, but if it started from something like this it might be pretty straight forward. Might even be able to use venturi inspired flow to turn a "turbo" that would be attached to a pump impeller.

Not sure if I fully understood your idea, but I think the venturi effect needs a reasonable medium speed to work properly. So a slow moving high volume creek probably does not create enough vacuum to drive mechanics unless you have the ability to restrict the whole creek (and therefore increase the pressure difference in between in- and outlet of the venturi to generate proper speed in the restriction).

I haven't done a good job of explaining what I was thinking which is driven by my circumstances. The creek I have is likely between 1-2m/s (3.6-7.2 km/hr), and the drop from one edge of the property to the other is not much, maybe .5m over 20m. If I could even get a small trickle, pumped 30ft horizontal, and 6 ft vertical, it would make my garden so happy, but my closest 110v power is a long way, 60m maybe. There is no option of a dam or flow restriction. I agree that a venturi's effectiveness is directly related to the flow velocity going through it. If I made a 200mm diameter flow tube, that lead to a narrowing restriction I might get 3-4 m/s in the neck? If I had a suction tube in the restriction, I could possibly use the draw from that to suck in a small piston, which should be directly attached reciprocating water pump. I've used something like this in air over hydraulic tools, where a compressed air flow is used to power a small reciprocating hydraulic pump. The other idea that I'm toying with is the paddle wheel and big spiral of pipe that's been used, but is a lot of material for a small amount of pumping.

Guess you don't need a Venturi at all. With this flow speed a ram pump should work without that. ,at least if you modify the parameters according to your situation.

I've built a small ram pump in the past, and have a few reference books on them. They all require at least a bit of fall for the water to accelerate down the pulse tube, generally a 20ft steel pipe is recommended as the pulse feed tube. What I'm looking for is something that doesn't need any head, instead just uses the horizontal flow of water.

I can't imagine, that a venturi could help you since the flow speed of the medium is always higher than the speed on the suction side. But this is just a guess and is not based on calculation. With ram pumps, the first thing I was wondering about, was that the valve that blocks the flow always points upwards. I think a long horizontal tube should envolve enough pressure when blocked frequently.