What determines hydraulic power?

[raeuber]

I am trying to find out if hydraulic power differs drastically with engine rpm on same size horsepower tractors. Is there maybe a "rule of thumb" that someone can share? What's everybody thinking on this?

 

[JCByrd24]

I'm not sure what exactly you're asking, but will try to help. Hydraulic power is simply proportional to pressure x flow. Pressure is related to how hard or with how much force you have to do something, flow is related to how fast.

Usually when comparing pump outputs on similar tractors, more flow (GPM) will mean faster loaders, if they're the same size cylinders. Luckily, most companies give not only cylinder size but operating pressure and cycle times as well to compare. The more flow at the same pressure, the more power it'll take from the tractor, but usually there is power to spare during normal operations.

If that doesn't help, perhaps you have a more specific question in mind?

 

[mmurphy]

No...Flow of course is slower at slower rpm's.

A rule of thumb is 1 hp (from engine) required for 1 gpm at 1500psi.

Now remember if you are running short on hp, you will also stall engine when dropping rpm.
Like the last post, I am not sure that is what you are after.

 

[raeuber]

Thanks guys, this is all great info. I guess I don't have a specific question, just wanted to get some info on hydraulic power.

 

[Texasmark]

Thanks guys, this is all great info. I guess I don't have a specific question, just wanted to get some info on hydraulic power.

Like JC mentioned, the pressure and area of the piston determine the force applied. Since area is half the diameter times it'self (squared) x pi, doubling the area of the piston increases the force 4x. Course you just cut your speed to 1/4 what it was for a given rpm and hydraulic pump as the volume to fill just went up 4x.....don't get something for nothing.

I was running a hyd cylinder on a home made log splitter off my Ford 3000. By the time I got a large enough hyd cylinder with enough diameter to split tough logs, my speed had dropped to a disgusting creep....but it works and beats the wedge and I had everything around the farm to build it.

Mark

 

[4520RX]

Hydraulic power is more dependant on the pump itself (rated on gallons per minute) and the engine RPM's Max pressure is limited by the bypass on the control valve. When I use my backhoe I get the best performance @ 1700 RPM.

 

[Texasmark]

Hydraulic power is more dependant on the pump itself (rated on gallons per minute) and the engine RPM's Max pressure is limited by the bypass on the control valve. When I use my backhoe I get the best performance @ 1700 RPM.

Sir this is apples and oranges. Your best performance obviously includes "rate of pressure application" as well as pressure application. I answered the question purely as a matter of pressure, i.e available hydraulic pressure obtained from whereever at whatever rpm and whatever pressure relief valve setting applied to a fixed cross sectional area....the area of the hydraulic piston. Once you move the object that you are applying this pressure to exceed the resistance of the object, you have now introduced pressure in motion which is referred to as Horse Power; lbs force x rpm/gpm/in/min/whatever + constant = HP.

Have a nice day.

Mark

 

[J_J]

Pressure and surface area dictate power available.

Increase either one and power increases.

Volume of fluid in GPM determines speed.

 

[Texasmark]

Pressure and surface area dictate power available.

Increase either one and power increases.

Volume of fluid in GPM determines speed.

So isn't that what I said? But I didn't refer to it as power. I referred to it as Force, static force to be exact. And force is not power. Power is force in motion.....hence horse power.

Speed is not force, but multiplied by force in lbs/square inch, + a constant of proportionality, it's power/work function, i.e. force in motion, hence work, hence an energy consumer (like gasoline is energy within it'self, but useless till consumed to do work, changing it's stored BTU's of energy to usable work by being consumed at some rate to do work), hence subscribes to the conservation of energy theorem.....energy is not lost or gained, merely converted from one form to another, heat as a loss in doing work if you are after something else, or heat, for thermal conditioning effects if that's what you're after. Physics 101, 201, 202, and 301 and 302.

Have a nice day.

Mark

 

[J_J]

Thanks for your effort in teaching Physics 101, and Hydraulics 101.

I gave a simplified answer direct to the point, based on a simple question.