2555 HST RPM question (Load Sensing ?)

[Uncle Hulka]

I have a question about my 2555 HST. I don't know if this is normal, but I just discovered that I am unable to get the engine RPMs above 2,400. I know that is the speed for PTO operation, but this is without having the PTO engaged. Just sitting.

Last Saturday I mounted a 3-point hydraulic reservoir/pump (30 gal if memory serves) to power my FEL-mount Erskine snow blower. I believe this unit requires approx. 45-50 hp. I did a test run and at first (with cold hydro oil), I couldn't get the engine rpm above 1,800. The tractor only has 14 hours on the meter and this was the first time the engine had been put under any real load. I let it run awhile (5 minutes). With the oil good and warm, I could now reach about 2,150-2,200 rpm.

I know the PTO on a 3555 HST is rated at 42.5 hp, but shouldn't I be able to reach at rated pto speed with the blower doing nothing but, well, blowing?

The 2555 HST has a "Load Sensing" button. I have never used this feature. From what I understand, 'load sensing' is tied to the HST, to slow travel speed under extreme load. Does load sense have any impact on PTO power, even if the load sensing button is not on?

Bottom line, does anyone have any idea why I am unable to attain a higher engine rpm than 2,400 under no load?

Thanks for any help!
Uncle Hulka

 

[Jabonee]

Just put a call in to my DSR. Let me see if I can get an answer for you.:thumbsup:

 

[Jabonee]

OK, DSR informed me that 2555 HST is rated @ 2300 RPM. Load sense will NOT effect PTO. ECU controls engine PTO load. Basically if the load on the PTO drags the engine RPM down the ECU should correct it.

 

[Uncle Hulka]

Thanks, Jabonee. Your reply makes sense, but doesn't explain what I'm experiencing. Did he have any ideas about what's going on with mine?

 

[Jabonee]

Yes, My DSR called back with more info. Engine max rated RPM is 2500 +-50. Thats throttle lever full bunny, no load.If you are not reaching that check the cable to see if your getting full pull on the sensor. Found out some other interesting things. 2300 RPM is the rating for max PTO HP. Get this though,The PTO shaft rotates @ 570 not 540. 2160 gives you PTO @540 but not max HP. :confused3:

 

[Uncle Hulka]

WOW! That is some very interesting information. Thank you so much. I'll check and see if I'm getting full-pull at the sensor. Something tells me I am, because I achieve maximum rpm well before I run out of throttle lever travel. Does that sound normal?

 

[Jabonee]

If your getting 2500 RPMs at full lever, you at factory spec.:thumbsup:

 

[Nortac]

Yes, My DSR called back with more info. Engine max rated RPM is 2500 +-50. Thats throttle lever full bunny, no load.If you are not reaching that check the cable to see if your getting full pull on the sensor. Found out some other interesting things. 2300 RPM is the rating for max PTO HP. Get this though,The PTO shaft rotates @ 570 not 540. 2160 gives you PTO @540 but not max HP. :confused3:

Can you please explain this a bit more for me? So running at 540 on the 2555 one is not actually getting the rated HP?

 

[Jabonee]

Can you please explain this a bit more for me? So running at 540 on the 2555 one is not actually getting the rated HP?

Yes that is correct according to my DSR. You should be running your 540 attachments @ 2160 RPM. 2300 RPM gives you Max PTO HP. I was told it was something to do with the gearing.:thumbsup: