Kubota B7800 HST correct operating RPM speed: Kubota Review  -- Kubota Tractors Discussion Forum and Review Kubota B7800 HST correct operating RPM speed: Kubota Review -- Kubota Tractors Discussion Forum

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 11-19-2010, 10:58 Post: 175242
bhaxel



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 Kubota B7800 HST correct operating RPM speed

I recently got a B7800 which has a hydrostatic transmission and I am wondering about something the previous owner told me. He said that running the engine slowly when going slow causes a lot of wear and to always have the engine speed above 2000 RPM. I've never opererated one of these before and I'd like to hear what some of you more experienced folks know on this subject. I thought it would be covered in the owner's manual, but it really isn't. The only clues are that the specification for "rated" engine speed is 2600 RPM and that to get the standard 540 PTO RPM the engine needs to be at 2600. Do I need to be running the engine at 2600 RPM regardless of ground speed? Thanks in advance...






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 11-19-2010, 13:13 Post: 175245
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 Kubota B7800 HST correct operating RPM speed

I own a NH T2210 (31hp) with HST transmission. My experience is limited only to the 120 hours I have on the machine. Although as I spend more time doing things, I find that I am usually operating it around 2000-2200 rpms. That is only just listening to the engine to hear if it strains or bogs down as I climb a hill with a load of manure. Brush hogging I will push it to the recommended rpms for the 540@ the PTO. Using the FEL to move gravel and sand usually the same thing--in low gear range. I have 3-gear ranges--Low, Middle and High--I am really, if ever in the high range--too many hills!

Hope this helps. I am interested in what others would have to add, too.






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 11-19-2010, 13:16 Post: 175246
AbbasChild



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 Kubota B7800 HST correct operating RPM speed

Oh yeah, if I am just heading back to the shop-garage for the day's end, and I am on the flatter spots I will drop the engine speed down to around 1700rpms.






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 11-19-2010, 15:42 Post: 175250
kthompson



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 Kubota B7800 HST correct operating RPM speed

No expect here but have about same size with HST also. My use has been in about same range as AbbasChild. Then mine idles about a 1,000 RPM it seems and it would never enter my mind to drive it at that engine range other than just to creep up or back for hooking up.

OK Art, Murf looking for your comments.






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 11-19-2010, 16:23 Post: 175251
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 Kubota B7800 HST correct operating RPM speed

First off, welcome aboard!!

The concept is, that lugging a hydro-static drive is a bad thing.

Not the engine, but the drive itself.

In order to know the 'why', you have to have a bit of understanding of the 'how' first.

A typical HST (Hydro-Static Transmission) uses a pump of a variety called a "swash-plate" pump. The engine drives a plate which has the ability to tilt away from the typical 90 from the drive-line. Think of it as a flywheel that is not fixed rigidly to the flywheel, but rather can pivot at that connection. That movable plate is what pushes the pistons.

The big advantage of this setup is that the same single pump has the ability to produce large volumes at lower pressure, or lower volumes at very high pressures, or anywhere in between.

This is what allows you to have 100% power at a creep, or moderate power at 'roading' speeds.

Now, the problem is that when you over-work the pump at the 'high volume, low pressure' setting it creates tremendous heat & wear. This is easily fixed by increasing the RPM's if possible, otherwise backing off on the pedal some.

However, working at proportional settings, that is load matched to power supply, is no problem at all. For just moving a machine say around a yard, 1,200 - 1,400 rpm at walking speed for example, isn't an issue generally.

Basically it will take a bit of time for you to get used to matching power provided, to the demand you've created. Say 1,400 rpm for walking speed, 1,700 rpm for jogging speed, 2,000 rpm for running speed when empty. Increase that proportional to added work, i.e. load on the FEL, pulling a trailer, etc., etc.

I usually tell people to set the throttle such that the engine is neither lugging, nor racing. If it doesn't sound right, it likely isn't right.

Best of luck.






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 11-19-2010, 16:44 Post: 175252
auerbach



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 Kubota B7800 HST correct operating RPM speed

The manual for my Grasshopper diesel zero-turn (hydraulic drive system) says to always work at full RPMs.






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 11-19-2010, 17:24 Post: 175254
earthwrks

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 Kubota B7800 HST correct operating RPM speed

Both my blue and yellow (New Hollands) mauals say "run at or near full throttle which is 2600-2800 RPM".

Murf knows (but forgot to mention) these modern diesels need top speed for good combustion.

Also, the charge pump which keeps the pistons pressed against the swash plate needs the proper engine speed to make pressure.

One way of "feeling" if you're lugging the system (not the engine) is the backpressure feel or resistance through the "go pedal"---a high resistance tells you wrong range (too high). However, a very soft or no resistance pedal is not a concern but can indicate that a higher range may work too.

FWIW, very rarely will an engine stall when running in too high a range; usually the system's relief valve will kick in---BUT that causes the oil to get hotter and create air bubbles in the oil which leads to heat and wear.






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 11-20-2010, 01:16 Post: 175256
candoarms



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 Kubota B7800 HST correct operating RPM speed

Bhaxel,


Before engaging the PTO, or engaging any power-driven implement, be sure to reduce your engine rpms. Engage the mower deck, tiller, or snowblower (for example) only when your engine is at low rpms. Once the implement is under power, you can then let out the clutch (slowly) and then begin to throttle up.

It's always best to use your PTO driven implements at full rpm and under full engine power. Just be careful when engaging them. It's never good to let the clutch out when the engine is making full power. (Very hard on clutches, PTO u-joints, mower deck belts, etc.)

When using your loader for delicate work, such as when near the foundation of the house, it's best to run your engine at lower rpms. This will give you very fine control of your loader operations and tractor ground speed.

All pulling operations should be performed under full engine power, such as when tilling, cultivating, mowing, plowing, etc.

Hope that helps.

Joel






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 11-21-2010, 17:31 Post: 175291
earthwrks

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 Kubota B7800 HST correct operating RPM speed

Quote:
Originally Posted by candoarms | view 175256
When using your loader for delicate work, such as when near the foundation of the house, it's best to run your engine at lower rpms.This will give you very fine control of your loader operations and tractor ground speed.



Joel I beg to differ. Doing as you precribed has no affect on the situation as locomotion is a function of the "go-pedal" as I call it. Lugging the engine in the interest of fine control is counterproductive and unnecessary. Precise and delicate work is where HST shines!






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 11-21-2010, 18:34 Post: 175295
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 Kubota B7800 HST correct operating RPM speed

Earthwrks,

Loader operations are greatly affected by engine rpms. Higher engine rpms cause the loader and bucket movements to become more rapid and a bit more difficult to control when performing delicate work.

I find that when using the forks to load a pallet in the pickup, I have much more control over the loader movements when the engine is running at about 1/2 to 3/4 throttle.

Joel






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Discussion Boards > Active Subjects > Messages as Posted > Kubota Review Forum

Thread 175242 Filter by Poster:
AbbasChild 5 | Art White 4 | auerbach 3 | bhaxel 2 | candoarms 4 | earthwrks 6 | hardwood 4 | hemrich@att.net 1 | kthompson 3 | lencamp 2 | Murf 1 |




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