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!!