CK 30 RPM's

garydc · Apr 1, 2009

JimmyJ I hope you are not planning on too much backhoe work for a couple of weeks yet as there is still a fair bit of frost in our area, I have mine on and did a couple of test holes last week as I wrote in another thread I had a tough time digging due to 1 1/2 to 2 feet of frost. Gary

Gittyup · Apr 1, 2009

I Had suggested in an old post that HST's should be operated at or near full throttle and some said that it was not necessary. As I didn't own a Kioti HST I didn't argue back. But, the manual for my John Deere HST clearly says to run at full throttle. Anything much less and you can hear the tranny straining. Sure makes sense because HST's rely on hydraulic pressure.

I even keep my rpms up a bit (>1500) all the time for my manual tranny. Just seems to reduce any tendency to ride the clutch and the tractor operates more efficiently too.

IslandTractor · Apr 1, 2009

IXLR8 said:
Hmm, this is the first I have heard of a 2000rpm min for HST use. I typically run between 1500-1800 as it gets the job done with minimum noise. The only time I run at 2000 or higher is when I want to get somewhere in a hurry and I am using high gear. I don't doubt what MI says, I would like to understand more the why such high rpm is required.

I do the same as you Jim. I tend to do routine tractor chores at 1500-1800 RPM as that is plenty of power and the engine is quieter. Mowing starts at about 1800-2000 and only with heavy grass or serious bush hogging gets me up to PTO speed. I also use the BH at 1500-1800 most of the time.

I must confess I don't quite understand the relationship of RPM to power in the hydraulics. I may be incorrect but I thought that the hydraulics are always at "normal" pressure and that only the gpm changes with RPM. If that is the case (and it is probably not that simple) then the only penalty for running at less than full PTO would be slower function. My experience however says that indeed I do get more power with higher RPM but I don't notice significantly different loader or BH power after about 2000 RPM.

joe48 · Apr 2, 2009

Sounds like we need to hear from Wallace and some of the other dealers to get the benefit of their experience and factory training.

I too run lower RPMs for noise and economy most of the time at the 1500 to 2000 "sweet spot"

Since I have over 600hrs on my 2003 CK20, and its mostly heavy dirt work and heavy bushhogging (at 2000-2600), I would like to know about anything that will increase longevity or reduce wear.
Makes me think its time to check the log book, must be about time for another hydro oil & filt change.

Joe48

MichiganIron · Apr 2, 2009

2000 rpm minumum for the charge pump of the hydrostat to properly feed system and keep up with the "losses".

If you look at the performance curve of the engine, it will torque out at approximately 2100 rpm, then fall off slightly above that. Your engine is running at top effciency at about 2100 rpm. Above that is "horsepower", the time dependant measure of how much "work" an engine can accomplish in an interval of time.

IslandTractor · Apr 2, 2009

MichiganIron said:
2000 rpm minumum for the charge pump of the hydrostat to properly feed system and keep up with the "losses".

If you look at the performance curve of the engine, it will torque out at approximately 2100 rpm, then fall off slightly above that. Your engine is running at top effciency at about 2100 rpm. Above that is "horsepower", the time dependant measure of how much "work" an engine can accomplish in an interval of time.

I understand that you get the most "bang for the buck" in terms of engine power and efficiency at around 2100 rpm. However, I am not clear on how it could be harmful to the HST to operate at say 1500-2000 engine RPM assuming the engine is not lugging.

MichiganIron · Apr 2, 2009

Probably won't.

The HST is a closed hydraulic circuit with a variable displacement pump and fixed displacment motor. With any closed system, there are losses (heat, etc.) To keep the the system operating at the proper pressure and flow, the charge pump continuously supplies a pressure head to the closed HST system. The system is designed to operate with the charge pump pressure head of 90psi. The charge pump is designed to supply the charge pressure of 90psi at about 2000rpm engine speed.

So....to have the HST operate as designed, 2000rpm supplies the proper pressure head. Loss of charge pressure can cause cavitation in the system.

VictorW · Apr 2, 2009

MichiganIron said:
Probably won't.

The HST is a closed hydraulic circuit with a variable displacement pump and fixed displacment motor. With any closed system, there are losses (heat, etc.) To keep the the system operating at the proper pressure and flow, the charge pump continuously supplies a pressure head to the closed HST system. The system is designed to operate with the charge pump pressure head of 90psi. The charge pump is designed to supply the charge pressure of 90psi at about 2000rpm engine speed.

So....to have the HST operate as designed, 2000rpm supplies the proper pressure head. Loss of charge pressure can cause cavitation in the system.

So I understand this correctly,

, the 2000 rpm is "only" for when you are using the HST....pushing, pulling, or just traveling. The bh and pto are independant of the HST and can be run at less rpms if you're not "moving" the tractor. And as always, don't lug the engine down for any operation.

MichiganIron · Apr 2, 2009

Exactly. For BH operation, we usually suggest around 1500 rpm until the customer gets comfortable with the machine. Most of the time, 1800 rpm is enough for backhoe operation.

The 2000 rpm suggested is for proper HST function.