Gear pump standard?

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hobgobbln
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Re: Gear pump standard?

Post by hobgobbln »

Bill Shields wrote: Sat Jun 04, 2022 6:36 pm I would drive a dc generator rather than a gear motor pump.
I also would much prefer electric methods but they want mechanical. That is my plan B if hydraulic doesn't work out though.
NP317 wrote: Sat Jun 04, 2022 8:49 pm Sounds like an outboard motor lower unit might work!
That's been my plan too. It will let me test out different props and already has the right angle mechanics in place. I"ll just need to adapt it to mate with the vertical shaft and pump.
BigDumbDinosaur wrote: Sat Jun 04, 2022 9:10 pm Now that we know something about the application, I have to ask why mechanical power transmission can’t be used.
That is fairly complicated so bare with me.

This whole thing is getting installed on a really big floating platform in a river. There will be a round opening in the platform (they're calling it a moon pool) that the prop and shafting will have to fit down through. The table looking part in my "sketch" :lol: will be bolted to the floating platform. On top of the raised platform will be a big metal sculpture of a bird. If that was all it was this would be easy. Here's the complicated parts:

-the river is called a "tidal river"? The direction of the flow of the water actually reverses during the day which I have never heard of. They sent me a graph of the river flow over a few days and its plotted just like a sine wave. Positive values are one direction, negative values are the other.
-the bird sculpture's wings need to move. I'm not building the bird so I'll need to figure out the mechanics of making them move later.
-the whole assembly, not including the raised platform, needs to rotate with the direction of the water essentially making the sculpture point in the direction of flow like a weather vane does in the wind.

Problems I need to overcome:
-most importantly, start telling the guy who takes on these nightmare projects no.
-the prop, vertical shaft and some sort of rudder cannot be bigger than the opening in the platform. There is no dry dock available for install and I was told divers are also not an option. So everything needs to be able to be lowered into the water through the opening. The opening is supposed to be round which also means I may have to make the lower portion off center so it can fit down through. That's one of the biggest reasons a mechanical transmission isn't feasible. Getting this to work at all will be challenging enough. Transferring the rotary motion of the prop through a bunch of right angles up to the top of the turntable is basically a fantasy.
-I need to build in some sort of speed limiter. I will have to engineer this based around normal water flow rates. I'm concerned that during heavy rain the water will move much more quickly and I'll need to make sure this won't rip itself apart. Thinking about trying to mechanically limit the speed makes my head hurt. With fluid power however, I should be able to handle it with valves. In theory at least.
-it needs to be serviceable. Everything breaks at some point. Prop breaks, bearing goes bad, whatever, the lower unit will need to be able to be pulled out of the water without calling in a crane to remove the entire structure in one piece. Another reason a mechanical transmission would be tough.

The only way I can think to pull this off is using fluid power to get the rotary motion from one place to another, so I need to start testing hydraulics which is why I'm asking about gear pumps. I've replaced hydraulic parts on equipment before and I understand the concepts of hydraulic systems, but this is my first time starting from scratch. I've also never tried to build something powered by a river and a prop. The theory and principals check out but, I won't know until I try.

So, can anybody recommend a small, commonly used/available cast iron gear pump? :lol:

Griz
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NP317
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Re: Gear pump standard?

Post by NP317 »

Another potential complication brought to mind by "cast iron gear pump."

Tidal rivers usually imply that salt water is involved. So salt corrosion becomes an additional consideration.
I don't mean to further complicate your challenges, but...
RussN
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Re: Gear pump standard?

Post by hobgobbln »

I did think of the salt water part too. From what I can find, the cast iron would hold up better than aluminum. I’m going to try my best to keep the pump up out of the water regardless though. I may need to make a gear box or pulley system between the prop and pump depending on how things work out. Keeping that up out of the water so I don’t need to water proof things will make it much simpler.

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liveaboard
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Re: Gear pump standard?

Post by liveaboard »

I used to live near Calais, Maine. 60' tides meant that all the rivers around were like that, the currents were just crazy.
And dangerous.

You don't need much power; fractional HP. Still, to get the pump to turn you'll need a prop intended for low speed. Grounding could also be a worry at low tide.
Boat propellers have a diameter, a pitch, and may have 2, 3, or 4 blades. It's a whole thing of its own.
A prop in a stream will turn with good torque.

Hydraulic drives are done all the time, but then you're talking 10HP and up (I installed a 10HP hydraulic bow thruster in a boat I have).

Your original question about fittings; there are standards, lots and lots of them.
Different flanges, bolt patterns, and shafts.
Cones, straight, spline, and I even have one with a slotted end.
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rmac
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Re: Gear pump standard?

Post by rmac »

I wonder if this problem could be at least partially simplified with a vertical axis turbine of some kind ... sort of like an anemometer, but stuck down into the water instead of up into the air. Such an arrangement would be indifferent to the flow direction, and it seems like you could transmit the rotary motion directly from the turbine to the guts of the sculpture with just a simple shaft.

-- Russell Mac

turbine.png
Bob D.
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Re: Gear pump standard?

Post by Bob D. »

I would fight for a concession on design criteria….. I would think a paddle wheel design is the way to go along with all mechanical drive. The least intrusion into the water, self reversing with flow, easy to make in any size or complexity. Not knowing what power you need real world, a paddle wheel can realistically be figured out with simple math. Pretty hard to beat the slow rpm torque that can be made. It may not be required to make anything really big.
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hobgobbln
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Re: Gear pump standard?

Post by hobgobbln »

liveaboard wrote: Sun Jun 05, 2022 3:21 pm Grounding could also be a worry at low tide.
Boat propellers have a diameter, a pitch, and may have 2, 3, or 4 blades. It's a whole thing of its own.
I asked about water depth and supposedly where this is going the average is 20' +/- 6' with the tides so I should be safe.
Yeah, I never knew there was so much to props until I started thinking about all this. Then I started looking at pumps and the migraine began :lol:
rmac wrote: Sun Jun 05, 2022 6:37 pm I wonder if this problem could be at least partially simplified with a vertical axis turbine of some kind
I don't think that would work very well in water. The cups will scoop the water just fine, but the drag of the water on the cups turning against the current will be much higher than in air since fluids don't compress. I found a video of a college in Germany(?) where they had done what you're talking about. Instead of cups they used airfoils or I guess hydrofoils to decrease drag and increase efficiency. While it did work, it bounced around and jumped quite a bit because of the constantly changing drag through the rotation. I'm going to try and stick with something like a prop so the drag is close to constant. Good idea though.
Bob D. wrote: Sun Jun 05, 2022 6:42 pm I would fight for a concession on design criteria
I tried that already. This is another one of those projects that sounds good on paper but is completely impractical. They are hell bent on the opening in the hull being round and 20' away from the edge of the platform. Why, I have no idea. So that complicates the paddle wheel idea. With a round opening I'm limited to a max particular wheel diameter. And if I need to increase the width of the paddles, I'd have to decrease the diameter of the wheel to keep from hitting the sides. Plus, I'd still need to have a rudder of some sort below the wheel to catch enough water to turn the bird. If I were able to build this off the side of the platform, I'd be with you 100%.

I really appreciate all the input and design ideas. I'm always interested in learning a better way. But what I could really use to get going is a recommendation on a very common, small gear pump. Or if there is no such thing, let me know and I'll just pick one. I'm not used to hydraulics so I may be asking for another unicorn for all i know.

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Re: Gear pump standard?

Post by liveaboard »

The cups are probably not the best for water, but I have seen a vertical shaft water wheel on a fairly large hydrogenator, maybe 50kw. It used to supply a small town.

It was 50 years ago and I can't remember the shape of the wheel. The river was routed through a deep narrow channel and the wheel was at the bottom, the generator mounted high above.

If you imagine some sort of guide or half tube, that would be easy to fabricate and lower down. It wouldn't have to be deep.

If you're hell bent on hydraulics, you need to look through catalogs for pumps and motors.
I used to buy from flowfitonline in the UK, but I assume you're in the US.

You can use a pump in reverse as a motor (I've done it). Hydraulic motors can run in either direction, pumps can't.
Look for graphs; there might be minimum speed for the pump.

I've fitted an unknown flea market hydraulic motor too, I just found a similar displacement one in a catalog and used those numbers.

Most likely you'll get small motors / pumps with straight keyed shafts that are easy to work with. I have bought a few, and have a few more on my shelves. You can get ready made pulleys (sheaves) for them, all sizes and types. I'm thinking small timing belt, 1/2" or so.

You'll also need a reservoir tank. With this application, you can forgo other components like PRV and controls, your pressure will be very low.

But from your description, I don't think hydraulic is the way to go; or did I miss something?
I'm not sure how far the bird is from the hole.

Oil lines are great for distance and twisting around obstacles.

You can use mild steel underwater if you use a marine coating (2 component epoxy marine paint for instance) West Marine is recommended for that sort of thing in the US.

Propeller should be bronze and shaft stainless. And you'll need a zinc anode, it's good if it can be replaced from above.

Maybe you could use direct drive, but if you use a conventional prop and horizontal shaft, most likely with space limitations you'll need a belt drive with your pump above the shaft.

Here's a picture of a bow thruster tunnel I made years ago; it's 2 feet under water, but it's possible to clear or even remove the prop without hauling out the ship.
bow thruster inside 2.jpg
The vertical pipe is usually dry inside, but there's a cover at the bottom that can be removed, which floods it to near the top. Then I can reach down to the prop. After closing it up again, the water is drained using the little valve at the bottom.
The yellow thing to the right of the vertical pipe is the hydraulic motor unit.

This is a shaft I made for my boat, with a prop I bought from ebay.
I sized the prop and direction as required, but since I needed to fabricate a new shaft anyway I didn't need any particular cone / key.
Propeller cone is by ratio, like 10/1.
propshaft propeller + nut fitted.jpg
Obviously, yours would be smaller.
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Re: Gear pump standard?

Post by hobgobbln »

liveaboard wrote: Mon Jun 06, 2022 4:18 am But from your description, I don't think hydraulic is the way to go; or did I miss something?
I'm not sure how far the bird is from the hole.
It may not be the best way but it's the best I can think.
From prop to bird is going to be around 14'. That coupled with multiple direction changes, not knowing how the mechanics of the bird will need to be made and that the lower assembly needs to be able to separate and be removable for install and service make me think rigid shafts and gear boxes will be a nightmare just waiting to explode.

Speed control is another issue. If there are heavy rains or if there are damns upstream that get opened and the flow rate increases a lot, I'd need to make some sort of braking system and someone needs to be there to operate it. Or I'd have to find/build a governor or centrifugal clutch so it can't over speed and rip the bird apart. I believe I can solve that with valves if I go hydraulic and it will limit the pressure or flow and just drain back to tank. Again, I'm new to designing hydraulics so I could be wrong there too.
liveaboard wrote: Mon Jun 06, 2022 4:18 am Oil lines are great for distance and twisting around obstacles.
Which is exactly why I've got fluid power stuck in my head. It's all going to be complicated to get working no matter what, but this seems the simplest way.

Griz
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Re: Gear pump standard?

Post by Bob D. »

I think any typical water propeller is designed to perform best in one direction. Any outboard prop is designed for really high rpms that you will never see. Not sure how successful you would be trying to adapt a really large prop to an outboard lower drive but that is a great way to go from a horizontal prop to a vertical drive shaft.
Generally hydraulic pumps all run at fairly fast rpms, 1725-3600 rpms. That will pose a problem.
If two hydraulic motors were plumbed together and one was turned the other would run as a slave.
I think you need to start with the propeller drive first. See what you make for rpms and torque. Then size hydraulics to that.
Might want to inquire about how much oil can be involved before the EPA has issues with a leak going into the water. Being unattended in operation they may well have concerns.
Going to be an interesting project for sure.
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Re: Gear pump standard?

Post by liveaboard »

There is a thing called a "proportional flow valve" that will limit the flow; that's an off the shelf solution to overspeed. They have an adjustment knob on them.
They cost $100-$200.

leaking oil; that's a good point.
Use biodegradable hydraulic oil. That's what it's for, and I used it on my boat in case of a leak. It's also used in tractors on "biological" farms.
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Re: Gear pump standard?

Post by liveaboard »

That hydro generator I mentioned I saw 50 years ago; I remembered it was pretty big but I thought it was just my memory because I was still small.
But I found a picture of it!
This is the actual machine I saw in Meddybemps Maine, being taken away for scrap.

dam-parts.jpg
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