hydrostatic pump education

[Everhard]

Can some one explain why a hydrostatic transmission (like what's in my tractor - Kioti CK2510) needs to be operated at an engine rpm higher then idle? I'm trying to understand how the pump will be damaged at low rpm? In my simple mind I'm just thinking the pump will simply be operating at a slower rotation, it's still full of oil, so what's causing damage? (Well I know the common warning of don't operate at low engine rpm but no actual reason why it's bad.)
I'm not a fan of blindly doing something without understanding why... So, can some one educate me, and I'm sure others as to the real reason behind what's happening in these types of transmissions that require higher then idle engine rpm?

Thanks,
E.

 

[Zmann.]

subscribed
I have had my ck2510 for about 2 years now I use lower RPM's all the time and only increase as the loads increase ,, not saying this is by the book but I see no downside to lower RPMs for light work
and no DPF on the ck2510 so nothing to worry about there

 

[4570Man]

I think you’ll find the engine power isn’t sufficient enough to do anything at idle. If you find that it works sufficiently well at 1500-2000 rpm then run it there. Running a HST tractor at full rpm all the time is mostly anti HST propaganda. You don’t want to constantly idle a DPF diesel either. But 1500 rpm or more is enough to make the DPF happy as long as it’s doing the work without bogging down.

 

[Everhard]

Understood. I'm not idling it if I need the tractor to actually do something other than move itself around the yard.
But ignoring the actual work being done, assuming no heavy load, just moving the tractor on level ground, is there any possible damage and how\why by running a hydrostatic transmission at say around 1,200 engine rpm?

E.

 

[repete]

My kid did this youtube video a while back on how they work.

 

[Everhard]

Lol when you said kid, I was expecting someone in primary school... (Hey I suppose he could be a teacher, he speaks really well.)

All joking aside, great explanation on what's going on inside a hydrostatic transmission. Presumably what's going on inside larger tractors vs the garden tractor transmission he pulled apart in principal will be essentially the same.

So. Seeing that, I'm still having a hard time understanding how anything can get damaged at low engine rpm? Like I said in my previous post, assuming you're simply moving the tractor, on a level surface, not making it do anything but move it's own weight.

E.

 

[MossRoad]

My old IH2500b HST had a light on the dash that would come on if the flow wasn't high enough. You either had to raise the engine RPM or let off the directional pedal to get it to go away. If it didn't go away at full RPM, there was most likely a plugged screen or filter, or, the fluid level was low.

I think the problem is if you are running at low engine RPM, and then do something that will call for high flow, you might cavitate the pump, causing air pockets, which could damage the pump. That's just a guess on my part.

 

[MossRoad]

Some machines have an auto sensing feature that automatically raises the engine RPMs to get the required flow from the transmission. That's probably the best of both worlds scenario. Keeps engine RPMS low until needed, saves fuel, wear and tear, etc.

 

[oldnslo]

HST transmissions require charge pumps which are used to provide make up oil in pump - motor loop that is lost due to leakage. As long as you maintain charge pressure the HST doesn’t care what speed you operate at.

Pump - motor loop is the circuit where oil leaves the pump, goes to the motor, leaves the motor and returns to the pump.

 

[MF243RedTop]

My old IH2500b HST had a light on the dash that would come on if the flow wasn't high enough. You either had to raise the engine RPM or let off the directional pedal to get it to go away. If it didn't go away at full RPM, there was most likely a plugged screen or filter, or, the fluid level was low.

I think the problem is if you are running at low engine RPM, and then do something that will call for high flow, you might cavitate the pump, causing air pockets, which could damage the pump. That's just a guess on my part.

Best answer... So far.. you can feel it in the sticks of a ZT like mine that doesn't have dampeners on the sticks connected directly to the pumps.
IMO, best to keep a minimum rpm when moving around and not completely at idle. Not sure if it actually cavitates but definitely not enough flow and pressure..and you can feel it. See what your tractor likes and doesn't.