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Hello friends! I have been on this site for long enough to know there are plenty of people here who understand hydraulics better than I ever will so I figured it would be a good spot to ask this. If two skid steers put out the same auxiliary hydraulic flow, lets say 35gpm, at the same system pressure, what is the significance of one of them having 75 engine horsepower and the other one having 90 or 100 engine horsepower? Thanks in advance!
 

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If all your wanting is an aux function that has 35gpm at a given pressure and the 75hp unit achieves that, than the 90hp and 100hp units will just burn more fuel. Think a hydraulic breaker hammer. Just sitting in one spot hammering away. Doesn't matter what size hp machine if the 75 achieves it.

If the same two skidsteers start doing
multiple functions then the gain goes to the higher HP units. The more 35gpm demand you draw the better the machine will perform with more hp.
 
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There is no advantage in your hypothetical of having higher horsepower. A good example is Deere's 3E series. They all have
the same hydraulic output and capacity. 3025e (25 hp), 3032e (32 hp), and 3038e (38 hp) all lift the same weight on the loader.
Now if your going to run something off the PTO, that's a different story.
 
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That's a good question. On a skid steer you have 2 types of HP. Engine HP and hydraulic HP.

Like anything, how much HP you need depends on how you use your machine. For a guy pushing a little snow, cutting some grass, maybe moving a dirt pile or leveling out a driveway you don't need much power. If this is all you're going to do a 45 or so HP machine will work fine, so why go larger? You would just be wasting money on a larger machine and fuel.

Now if you're going to do alot of digging, maybe cutting heavy brush or trees with a mower instead of grass or maybe heavy lifting; you need more thank 45 HP. Will 45 HP do the job? It might, but it will be slow going.

The hydraulic system is similar to the engine HP requirements I referenced above. For the most part, two machine with equal engie HP, GPM and hydraulic pressure will do the same work equally. If one of those has more engine HP the hydraulics will have faster recovery time. This would matter with a snow blower or more noticeably with a forestry mulcher. The machine with more engine HP will keep that mulcher head at a constant RPM for a longer period.

Engine HP also comes in when you need more gallons per minute. You won't see a machine with 75 engine HP that has a hydraulic system with 45 GPM. You need engine HP to create more gallons per minute. Usually you are around d a 90 HP or larger engine HP to get 45 GPM.

Use this form for calculating the Hydraulic (fluid power) horsepower.

HP Calculator PSI : GPM: HP = _
Formula: HP = PSI * GPM / 1714

PSI is gauge pressure in pounds per square inch; GPM is oil flow in gallons per minutes.

Rules-Of-Thumb:

Horsepower for driving a pump: For every 1 HP of drive, the equivalent of 1 GPM @ 1500 PSI can be produced.

Horsepower for idling a pump: To idle a pump when it is unloaded will require about 5% of its full rated horsepower.




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