Hydraulic motor power vs speed

   #1  

musselmark

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Generally speaking, if a larger displacement hydraulic motor is geared up with chain and sprockets to achieve the speed of a faster smaller displacement motor, will it still have more power (torque) than the smaller motor?
 
   #2  

oldnslo

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With same hydraulic inputs of flow and pressure the torque output at same speed will be very similar
 
  
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musselmark

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I'm trying to compare motors with quite different displacement. A 23 ci/rev 4500in-lbs motor which turns at 150rpm gear up to match the speed of a 5 ci/rev 1500in-lbs motor that turns at 750 rpm. My application is I have a winch made with the 5ci motor and it is geared down with chain and sprocket to give me the amount of pull I need. Problem is it is very slow. Would using the 23ci motor geared up give me equal pulling power but also a faster speed? Or ultimately do I need an engine with more hp.
 
   #4  

oldnslo

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Mark
If you require 750 RPM output from the 23 CIR motor you would have to gear it up at 5:1 ratio so torque would decrease by same 5:1 ratio or you would only have approximately 900 in lbs

Possibly use two speed motor so lower torque run high speed higher torque run low speed. Would have to check with motor manufacturers to see if they can be shifted under load
 
   #5  

Dave M7040

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oldnslo is addressing the issues very well!!

The one aspect of the motor input you have not mentioned is tractor engine speed.

The hydraulic pump, assuming it is an Open Center design, will have an increase in flow proportional to the increase in engine speed.

If you are currently doing your pulling with the engine idling, how does it behave at full engine rpm?

Depending upon your answer, a pressure compensated flow control may give you the ability to power in fast when winch load is low and then slow down when the load increases. A bit like the dual speed log splitter setup.

I would have to give this a lot more thought before making a recommendation.

Dave M7040
 
  
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musselmark

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Sorry this is not on a tractor, its on a boat. The hydraulic power unit is run from a 9 hp honda. I thought about the log splitter pump but I am running a 5 spool valve which also controls the boom cylinders. The entire system works good now other than it takes about 15 seconds to pull in 20 feet of rope with 1000 lbs on it. I'd like to bring that down to 7 seconds or so. But as its geared now, it's at its max for pulling power so cannot simply change the ratios on the sprockets or will lose the power I need.
 
  
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musselmark

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This is the winch
 

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   #8  

Dave M7040

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What I see looking at on line hydraulic motor calculators is:

For:
5 ci/rev 1500in-lbs motor that turns at 750 rpm. requires approx 15 gpm at 2,000 psi
23 ci/rev 4500in-lbs motor which turns at 150rpm requires approx 16 gpm at 2,000 psi

In other words, I do not see a lot of difference between the two motors....... they consume the same gpm while turning at a speed difference ratio of 5 which happens to be the ratio of the motor displacements.

Tell us more about your pump driven by the 9 hp motor. Your operating pressure too.

Have you asked about the 23ci motor because you have one?

Are you open to buying a different motor?

A calculator to show the HP required to drive a hydraulic pump producing 15 gpm at 2,000 psi is 21 HP.

This is real HP not what a gasoline engine is rated at.

It may turn out that you do not have the engine power needed to drive the motor you want and further, you are not driving the existing motor at the speed you think you are.

Have you done anything to establish exactly what speed the 5 ci motor is running at.

Dave M7040
 
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musselmark

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The pump is a .36 ci gear pump. Ya open to any motor. No idea what pressures the system is running at as there is no gauge. At the end of the day, is changing the displacement of either the pump or the motor basically doing the same thing as changing the sprocket ratio in terms of speed vs pulling power?
 
   #10  

Dave M7040

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To provide more helpful answers you need to measure pressure motor is running at.

A 0-3,000 psi gauge is $30

gauge

The speed of the motor also needs to be measured.

A cheap strobe tach can do this for you.

tach

Is you pump a direct drive off the engine shaft?

Dave M7040
 
 
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