Engine RPM VS Loader Lift Capability

[Henro]

I just want to confirm something since I occasionally miss the obvious...

It seems to me that GPM flow from the tractor's hydraulic pump would be a function of engine speed, with max flow being reached at max engine speed.

But as far as system pressure goes, that would be set by a relief valve somewhere in the system. And system pressure when using the loader would be the same regardless of engine RPM.

So at any engine RPM, the loader will have the same lifting ability. It will just move faster if the engine is running faster.

The loader will pick up the same maximum amount of weight at any speed, and that's it, right?

I'm referring to the normal tractor open-center type system...

 

[Bird]

</font><font color="blue" class="small">( So at any engine RPM, the loader will have the same lifting ability. It will just move faster if the engine is running faster. )</font>

That theory sounds OK, but the reality is different. I'm sure no expert on hydraulics and how much pressure the hydraulic pump is putting out, say at engine idle, vs how much at higher RPM, but I do know from experience that the loader would lift loads at higher RPM that it couldn't lift, or at least couldn't lift to full height, a lower RPM.

 

[gone]

Bird you would be right at lower rpms the pump won't overcome bypass in the pump itself. a small amount will seep past gears within a gear pump the out side of meshing gears is where the fliud is moved,since the gears have smaal clerance to pump body the fliud can bypass,untill pump puts out enough flow to over come the bypass,more prussure more bypass.

 

[_RaT_]

I was all set to post much the same. While the pump could produce an equivalent pressure at low RPM's and not have to account for the small losses, it would be a very tight tolerance pump. My experience is that the older the equipment, the greater the seepage gets and therefore the higher the RPM just to overcome the pressure loss from seepage be it from around the pump gears to the hydraulic cylinders to the spools.

 

[Henro]

Thanks guys!

Makes sense that if there is leakage in the pump [which there may be in most/all tractor pumps] that pressure would build along with flow as rpm increases.

I was wondering if it was my imagination that the loader seemed stronger at higher rpm. I thought I might be equating speed with power. Guess not... /forums/images/graemlins/smile.gif

 

[ns_in_tex]

I ran a test on my L4610 with a hydraulic flow meter, in the past to determine this.
I recorded:
@ 1500 rpm,
Pressure = gpm
0 = 6.25
1000 = 5.75
1500 = 5.75
2000 = 5.75
2200 = 5.75

@ 2800 rpm, 2000 psi = 9 gpm

this seems to go along with what others say, but it seems it may reach max leaking long before max rpm.

I didn't record max pressure, but did record it would pump 2000 psi @ 975 rpm with 4.25 gpm.

 

[keeney]

At very low RPM's (idle), you can also stall the engine before developing the max pressure because the torque curve does fall off a bit down near idle.

Pump performance may vary significantly with oil viscosity as well.

- Rick

 

[frank_f15]

AS BIRD SAYS" I AIN'T NO EXPERT ON HYDRAULICS) but i do know , from personal experience more engine rpm seems to make eveerything work faster and better.

 

[_RaT_]

Work faster, but not always better. Run a hoe on full tilt and watch how much jerking can occur. It's harder on the equipment at times as well. If I run my loader at full RPM, it operates so fast that it can get unreasonably difficult to position accurately without choking down on the loader valve which can take longer then just dropping the RPM's a little.

 

[B2400]

I agree. The "sweet spot" for my B2400 is @1900rpm. Loader has good hydraulic power and operates at a smooth and easy to control speed. Side benefits are less noise and better fuel consumption rates!!

 

[_RaT_]

I find my L3830's sweet spot is at very close to that, about 2000 RPM. Funny thing is, at 2000 RPM, it is still amazingly quiet.

 

[frank_f15]

Rat: sorry , pehaps i was not clear in the last post. i did not mean to say i run wide open , usually for Fel work i run about 1800 or 1900 rpm. give me good power and not jerky.

 

[frank_f15]

seems the sweet spot is the same for both our B2400's /forums/images/graemlins/grin.gif

 

[_RaT_]

No, no Frank, no apology, I knew what you meant and was really clarifying it for others. Did not mean to imply you don't know what your talking about. I was just out digging with the loader for a new irrigation main. I was at 2000 RPM and could still hear a car drive up. It is a real delight to operate at the lowest useable RPM. So smooth!

 

[jinman]

RaT, I understand the "jerky response" and I also think that a person who uses a piece of equipment until it becomes an extension of himself can run at much higher power and not jerk his tractor than the average person. It's like getting used to the clutch on your vehicle and then going to one that feels different. It takes awhile to adjust. I have noticed that full-time operators go at speeds I'd never attempt, especially those guys with the excavators who are swinging around, stopping on a dime, and dumping the bucket into a dump truck. If they misjudge by a foot, it cost big $$$. /forums/images/graemlins/blush.gif

 

[_RaT_]

First of all Hi Jim. How's that joystick? I agree with your statement. I know a fella that has pretty much become the surgeons or surgeons when it comes to hoes. He said for him, operating at the lowest speed is always a bonus for noise, wear and fuel use since he does it 8 hours a day almost everyday. When the digging is easy like in good clean soil, he says he just fires it up and digs as fast as the machine allows. On the job he's at now and been there for a little over a year, it's all rock and he throttles it way down because it takes away the noise and fuel use. You make a good point though.

 

[jinman]

RaT, my hose-clamped joystick is still performing flawlessly. I keep expecting it to give up, but it just goes to show you that "back yard engineering" sometimes is better than the stuff coming out of the factory. /forums/images/graemlins/smile.gif

I'm wondering what the effect of throttling back is on a Kubota HST transmission? Can you get enough power to spin 3 tires at 2000 rpm or less? I find that if I have any down pressure from the loader or an implement on the 3PH, I need about 2,500 rpm to spin my wheels. When pushing brush, I leave the tractor at 2500 and I win most battles against small trees. Of course, it also depends on the type of soil beneath my wheels, but for me, there is a big difference between 2,000 and 2,500 rpm for power to the wheels. However, the loader seems to have as much lift power at 2,000 rpm as it does at 2,500. What's your take on this?

 

[_RaT_]

No question Jim, the HST will take all you can give it and if you have some more, it will take that too. I find using the loader for digging and delicate work works best at 2000RPM and if doing loader work where I 'm moving material around, I'm up closer to 2300 to 2500 and in medium range. It all depends more on the circumstance I'm working with. I find I rarely spin the tires. Part of it is inherent though in that I run the pedal based on engine RPM drop/increase. The joy joystick is alive and well, all is right in the world. /forums/images/graemlins/wink.gif Rat...

 

[JasonMac]

All I know is my loader has more power at a higher RPM. When I have a full bucket of wet loam or clay, when breaking out of a pile, my loader may lift it about 3ft, when I keep holding the loader lever back, and raise the rpm the loader instantly responds and can lift the load to full height without a problem. I've tested this before, out of my own curiousity