BH-90/Operational RPM

[Jibber]

After reading a separate thread on RPM speed while using a backhoe I realized that I have probably been running my engine faster than needed while using my BH-90. I've never had a problem though, and have been able to control the movements of the boom and dipperstick without jerking it all over the place.

My question.. What relationship does RPM have to the power exerted by the hydraulics on the hoe or loader for that matter? Is it just a question of the fluid flow being slower so movement is slower.. but the power remains at 100%? Or, is there some dropoff in power at lower RPMs?

Thanks.

 

[_RaT_]

The pressure remains the same but the flow rate is decreased with a decrease in engine RPM. This can give the apppearance of decreased pressure, but if you had a pressure gauge you could see the hydraulic pressure is still being allowed to reach the specified PSI before being bypassed. I know a professional hoe operator that pretty much uses the fastest speed suitable for the job. If its tough rocky soil, he slow's it way down, in clean loam, he has it going fast.

 

[Jibber]

That's what I thought.

Like a hydraulic jack. It doesn't make any difference how fast you pump up and down, it's still only going to lift so much.

 

[CTyler]

I have not had the same experiance. Reving the RPM's higher provides more force. I haven't noticed this on the BH but have on the 3pt.

For example when lifting a pallet of bricks it would not lift it until reving up around 2400-2500.

 

[rbargeron]

I think everyone is right - to a point. Higher engine and pump speed makes more flow volume. The relief valve tries to regulate it at the upper pressure limit. But the valve's back pressure does vary a little with flow rate so you do in fact get a bit more system pressure at higher engine rpm. Just not a lot.

Customary cheerful refund if bogus.

 

[Kelvin]

To me this question would be very similar to the question "what RPM should you use for FEL operation?"

I think that the hydraulic system pressure regulators attempt to maintain the pressure at some upper limit, and under a "no load" condition the pressure could easily be maintained at nearly all engine RPMs.

Heavier loads would have a tendency to utilize (bleed off) that pressure more quickly, thus a higher engine rpm would be needed to maintain the pressure.

For example, my FEL has full range of operation with the engine at idle. However, I have to bump up the RPM to 1/2 rated rpm or more to get enough force (pressure? hydraulic flow?) for the FEL to raise the tractor's front wheels off the ground. And, the FEL obviously works faster with higher RPMs.

With my FEL and limited excavator (trackhoe) experience, I normally use the minimum engine RPM necessary to satisfactorily complete the job, and occasionally use nearly full throttle to get certain tasks accomplished. This may or may not contradict operator's manual instructions. If I can remember, I'll check my FEL manual to see what comments are there.

Kelvin