elongated impeller

[MaxFlow]

I need to make a foot long impeller that would fit nicely in a two inch piece of pvc, does anyone have a fairly easy outlook on construction materials and proceedures to accomplish this?

[wdyasq]

All impellers I have seen are much shorter than the diameter of the pipe.  Is there some now law of hydrodynamics you have uncovered?

Ron

[maker of toys]

wdyasq has the right of it.  1' x 2" is an unusual shape.  at the very least, you're going to need a bearing at each end of the impeller if you want to achive reasonablably efficient tip clearances.

we'd need to know flow rates, proposed rpm, proposed pressure differential and whether you intend to pump or generate with the impeller.  

from what you've said thus far, it sounds like you're envisioning an archemedes' screw, which is a drag-type device, and far better suited to high-volume, low-pressure, low rpm water/granular solids raising than any other task.  Archemedes's screw does have a high tolerence for 'trash' in the substance it's pumping. . .

for high speed, you could get an axial-flow drum pump and modify that. . .  

or stack a bunch of model boat propellers on top of each other if you're dead-set on a 1 foot length. . .  otherwise, you're in for some quality time with power tools.

you could make an archemedes' screw with copper flashing, a piece of thick-wall copper pipe, some tin-snips and solder. . .  the trick would be to lay out the 'screw' portion on the flat material.  a high-school geometry text might be useful, but some experimentation would probably get you there, too.  remember to leave material for 'tabs' to solder the 'vanes' to the 'axle'.  alternatively, you could cut up copper unions to provide propeller-type blades. . . less layout hassle, more cutting.

-Dan

[MaxFlow]

it is a low RPM crank speed, with somewhat archemedian design aspects, the whole impeller will always be submerged in water, some of the other aspects of the project I'm going to hold back for now, sorry.

Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.  Archimedes

[MaxFlow]

this part doesn't generate power but down the line it will, by help of another component.

[Ungrounded Lightning Rod]

it is a low RPM crank speed, with somewhat archemedian design aspects, the whole impeller will always be submerged in water

Then an archimedes screw won't work.  It requires alternate fluid and air to function.

[maker of toys]

I beg to differ.  some of the early ship propellers were more achimedian in form than anything; they ran completly submerged and they still beat the paddlewheel for grip on the water and efficiency. (which just goes to show how lousy the efficiency of a paddlewheel is in propulsion service. . .)

in any event, generating power with a screw is going to be problematic. . . an achimedes' screw is a non-reversable pump.  'Non reversable' in almost all contexts equates to 'low efficiency'

if you're using it as a pump, however. . .   you could make a reasonable approximation of a archimedes screw by heating up (way up; like red hot)) a piece of flat stock and twisting it axially a bunch of times.  getting it to run straight will be a challenge, but hey- no machine-shop required.

good luck.

-Dan

[MaxFlow]

Since it will be turned slowly I was considering this experiment, useing a half inch piece of pvc for the center, and spinning around it the foam that they use for weather stripping, the one side has the adhesive on it, and although I could get larger dimensioned foam, I was thinking of useing 1/4 inch by 1/4 inch, running up two concentric spirals, then putting overlapping pieces over this until I got the outside diameter that I wanted, once it is to the right size, I would coat the whole thing with epoxy, or possibly the stuff that made clackers, which I've got the recipe somewhere around here, for those who don't remember clackers they are two pretty unbreakable glass balls that were on strings, and by smacking them together they would do a pedulum type of movement, I guess it shows my age.

The center piece will be filled with a hardener, and capped so I wouldn't need a bearing at the top just a guidance pin inserted in the hole collar, the bottom would be set with axil and gear.

[Ungrounded Lightning Rod]

I assumed he wanted to pump water up a non-trivial head with a low RPM.  Without the  water being broken into into chunks that sit in moving bowls by buffers of air the water will just run back down and, even if he gets some pumpit, it will be dreadfully inefficient.  (With the water/air boundary it's very efficient.)

If all he wants is thrust - pushing  water around without significant backpressure - it will work.

[maker of toys]

Right-  I see where you're going with the air/water requirement. . . . my experience with screw conveyors was blinding me to the syphon effect.

[MaxFlow]

So your saying, that because of no air involved it will be a non existant force?

Ok, back to the drawing board....

[Ungrounded Lightning Rod]

There will be a force.  But you have a wide-open pipe back down.

It's just like pumping the water into an outlet pipe that you ran back into the water source:  Essentially all your water runs back (though you can tap a litte off the high point on the way) and most of your energy goes into the friction of the water in the piping.

If you have the air gaps it's like a bucket-pump water wheel or string of buckets on a rope or chain: lifting slugs of water efficiently with little friction and no opportunity for the water to run back down.

[MaxFlow]

Thanx everyone for helping me see a little further!

[ignesandros]

I'm not sure those commenting understand what you're talking about. You mean an impeller with a pipe for a shroud? Sort of an in-pipe turbine generator? From this perspective, the difficulty would be in tranfering the force to a generator without reducing the force you're tapping. How swift is the water you're planning to harness? What I envision from your desciptions is more like a turbine and less like an Archimedes pump.

-Andrew

[MaxFlow]

Andrew wrote>  I'm not sure those commenting understand what you're talking about. You mean an impeller with a pipe for a shroud?

Yes and no, but was thinking corkscrew type force in pipe, the end result I was looking for here was a minimal amount of pressure of the water on the outflow end, it doesn't need to be much

Sort of an in-pipe turbine generator?

No, just to get a minimal force upwards of water

How swift is the water you're planning to harness?

It's still

[ignesandros]

How far do you need to lift the water? How many GPM/LPM do you need? I can probly conk something out would have similar properties to what you've stated.

-Andrew

[MaxFlow]

about three feet

[MaxFlow]

the amount doesn't matter, I need a little compression of the water in the two inch pipe that's all.

If possible by other means, I would be interrested in what you might think