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Gear speed multiplier for pump
2

Gear speed multiplier for pump

Gear speed multiplier for pump

(OP)
I have an unusual situation where I am trying to run a pump manually with a mechanical device that is very slow (40 RPM max) but high torque (1500 in-lbs), while the pump should be run closer to 1500 RPM and 100 in-lbs torque.

Most gearheads seem to be made to reduce high speed motors, while I'm looking for the opposite (convert manual crank to motor speeds). Is this as simple as turning a gear speed reducer around the other way? Any advice where I can find what I'm looking for?

RE: Gear speed multiplier for pump

You need magic. Your power out is greater than your power in.

RE: Gear speed multiplier for pump

(OP)
How could I calculate the maximum possible output from my input?

RE: Gear speed multiplier for pump

Find out how to calculate rotational power (hint: your physics and/or machine design textbook should have it). Theoretically Pin = Pout, but in reality, Pout = Pin - Ploss (where Ploss is lost power due to noise, friction, etc.) Where'd you get your degree, by the way?

RE: Gear speed multiplier for pump

I don't know what you are trying to accomplish. The pump demands ~2.5 HP to put out at the rated capacity, but you are driving at very, very slowly and are not getting even remotely close to that.

RE: Gear speed multiplier for pump

(OP)
I rechecked my pump requirements, see attachment. My initial estimates where slightly off. If I want 125 PSI with the 3/8" port looks like I need 900 RPM, 45 in-lbs, requiring 1/3 HP based on the performance chart.

My crank input power, P = 125 (ft-lbs) * 40 (RPM) / 5252 = 0.95 HP

0.95 HP >> 1/3 HP

What am I missing?

RE: Gear speed multiplier for pump

I agree with the others. Your input power is already 2.5 times too low(not including losses) for the required output.

Kyle

RE: Gear speed multiplier for pump

latest info [900 rpm * 40 in.lb (output)] < [40 RPM * 1500 in.lb (input)] which doesn't violate any laws
first info [1500 rpm * 100 in.lb (output)] > [ 40 RPM * 1500 in.lb (input)] which is not possible

1500 / 40 is a 37.5x speed increase, which seems a lot to me. A quick internet search didn't turn up anything higher than about 7x speed increaser, and those are way too big for your application.

Perhaps you would have better luck using a small DC generator and DC motor to accomplish the speed change? You could also look at a generator + battery + PWM controller if you need variable output speed/power.

RE: Gear speed multiplier for pump

900 RPM * 45IN-LBS out < 40 RPM * 12IN/FT * 125FT-LBS in, so that's a good start over the original request.

The next problem is the 22.5:1 Output to input ratio. That's a pretty large jump in ratio; maybe 3 stage spur gear or two stage planetary. It might be cheaper to get a motor that is matched to the load; likely to be more reliable.

RE: Gear speed multiplier for pump

"I am trying to run a pump manually "

What does this mean??

ivymike - you typed faster than I did.smile

RE: Gear speed multiplier for pump

Power = Torque x rads/sec

For the given pressure and flow, your pump needs 0.333HP

You want more flow, so the pump has to turn faster. Increasing the speed leads to a lower torque, but the extra flow generates extra pressure and pressure x flow means more power...which needs more torque.

You need to work out how much power you need, as a function of the required pressure and flow.

Add in the efficiency losses.

That will tell you the total power you need.

HPost CEng MIMechE

RE: Gear speed multiplier for pump

(OP)
Obviously I would use a motor if possible, but this must be a purely mechanical system. The rotational input I have described is the only source of power. Essentially I am trying to gauge the feasibility of a manual input hydraulic system. Pump selection is not final, but it needs to be stainless, bi-directional (reversible), and around 125 psi, 1-2 gpm. Struggling to find something that will work with my slow input.

RE: Gear speed multiplier for pump

If you intend a human operated crank, recognize that this is close to World class athelete performance levels for short durations.

"A trained cyclist can produce about 400 watts of mechanical power for an hour or more, but adults of good average fitness average between 50 and 150 watts for an hour of vigorous exercise. A healthy well-fed laborer over the course of an 8-hour day can sustain an average output of about 75 watts.[1] The yield of electric power is decreased by the efficiency of the human-powered generator." Wikipedia: Human Power

RE: Gear speed multiplier for pump

(OP)
A hand crank is a good way to think about it, but it's a robot not a human.

RE: Gear speed multiplier for pump

Regular bicycle chain drives are about 5:1 max speed increasers handling power in the range you are looking for; put them in series to get appox. 25:1 total and that would be close to what you want.

RE: Gear speed multiplier for pump

Quote:

but it's a robot not a human

What?

So you intend:
Power source --> Motor of robot --> Mechanical, hydraulic, pneumatic or whatever linkage --> Robot "arm" --> Crank handle --> Speed increasing gear train --> Pump

Don't you think that it would be more efficient to do:
Power source --> Jumper cables from the auto part store --> Motor --> Pump

RE: Gear speed multiplier for pump

(OP)
Yes, but it must be done the first way you mentioned, hence why it is such a challenge. Imagine a Mars rover with a crank arm on it, and you want to drive it around and crank the pumps which are not connected to any power source.

RE: Gear speed multiplier for pump

What is the business case for requiring that something be done in the least efficient way possible?

RE: Gear speed multiplier for pump

Rino has small speed increasing gear boxes, but not in the ratio you need. I guess you could, however, stick two of them together - (1) at 1/5 and (1) at 1/6 that gives you an input speed of 30 RPM.

RE: Gear speed multiplier for pump

low rpm source --> positive displacement pump --> hydraulic motor --> high speed pump --> Nobel Prize in economics

RE: Gear speed multiplier for pump

Driving a crank arm with a crank arm introduces an orbiting force on both objects, which gets worse if the shafts are not perfectly aligned, or if either object has any compliance in its suspension. The vibration produced will be, at least, unbelievable.

Did I mention I think it's a bad idea?

Have you considered hydraulic quick-connects?

Have you considered multi-jaw couplings with a guided/compliant shaft, starting at ~zero speed while coupling and at pump speed while coupled?

Have you considered an eddy-current or other magnetic coupling?

Have you considered a flat plate friction coupling?

Mike Halloran
Pembroke Pines, FL, USA

RE: Gear speed multiplier for pump

(OP)
For what it's worth I drew a simple diagram to show what I am after. A special handle can be made to attach to the gearbox input shaft for the crank arm to latch onto. That's not too problematic, especially at the speeds of the crank arm. It's the gearbox that I am not sure is possible.

RE: Gear speed multiplier for pump

One component that needs to be considered is a place to react the difference between the input and output torques and any non-torque reactions.

RE: Gear speed multiplier for pump

I was going to suggest a rack and pinion setup with something to let you accept reversing motion on the input, but perhaps you can use a friction drive like an old bicycle headlight generator...a 1 inch rubber wheel riding on the OD of a bicycle wheel...robot turns the bike wheel and little wheel turns the pump. You could probably even turn a cogged belt inside out and mount it on the bike wheel with rubber cement, and then 3d print a cogged little wheel for the pump.

RE: Gear speed multiplier for pump

What flow do you need? It looks like you are using a pressure requirement to select a pump when you should be using a flow requirement.
Use a larger pump that will deliver the flow you need at 40rpm speed.

Ted

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