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Proper PTO ang velocity (rpm)

Proper PTO ang velocity (rpm)

Proper PTO ang velocity (rpm)

We're designing a tractor that will have a front mounted PTO and quick connect system and I am unclear on a couple of issues, any response would be greatly appreciated.  I am trying to figure out what speed (rpm) the front PTO should run at, I understand that the standards for rear mounted PTO's are 540rpm or 1000rpm but have been told that a front mounted PTO may turn much faster (at engine speed).  Also, does anyone know why the accepted values for rear PTO is 540 rpm or 1000 rpm?  Secondly, I am wondering if there is an accepted value for comparing engine hp to PTO hp, I have found through research that PTO hp is approx 80-85% engine hp.  If I know the design requirement of the power plant is 45 hp may I take that as the PTO hp for initial calculations or must I compensate for losses within the system?  The only way I can see doing that is testing a similar power plant and obtaining the PTO hp experimentally.  Thank you in advance for any information, Ryan.

RE: Proper PTO ang velocity (rpm)

Refer to:
ASAE S203.14 Front & Rear Power Take Off for Agricltural Tractors
ASAE S207.12 Operating Requirements for Tractors & Power Take-off Driven Implements
If you are looking at Europe, check the ISO standards, I believe 500 and 8759 relate to PTO's and also the CEN standards.

RE: Proper PTO ang velocity (rpm)

PTO hp is tested on a dyno.  Depending on the drivetrain etc the losses vary.  Some models are known to have high pto output relative to engine rated hp, these models tend to have gear transmissions and hydraulics which do not circulate fluid when not in use.

I have a hydrostatic transmission tractor rated at 52 pto hp, the pto hp is listed as 42 I believe.  The gear model and powershift models have 46 pto hp.

You should have a good idea of what your drivetrain and pump losses are by comparing to similar models.

I don't know where 540 rpm originated from but I know the 1000 pto rpm grew out of a need to transmit more power through a similar sized shaft.  I believe international had explored the limits of metalurgy with a close to 100 hp 540 pto output on one of its machines in the 60's.

RE: Proper PTO ang velocity (rpm)

I concur with Slowzuki.

I rule of thumb that I have heard is that the PTO power is ~85% of engine power, and drawbar is about 85% of that. Transmissions have a lot more parasitics than PTO's including more bearings to turn, more gear meshing friction, multiple clutch packs, tire slip, ground friction, etc. The engine power that you will require will depend on your drive system.

Also remember that 540 and 1000rpm are maximum speeds, not constant. I have also never heard of a tractor PTO running engine speed. Maybe a PTO on a truck transmission would?

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