21 vs 16 cc Pumps-Power Drain Question

[Ridin' Green]

Originally Posted by djagusch

You are making this more complicated than necessary. 21cc pump pushes 21cc's of fluid per rev at certain rpm's. Depending on wheel motor size it affects the revs of the wheel motor.

The major difference in hydro system design besides pump/wheel motor size is the pulley's and what rpm the mfg's are designing the pump to run at. Some mfg's have it set conservatively and some have it close to redline of the pump.

Maybe you and puppy are saying the same thing, but I think you just shortened it, because this is what I always thought too. If I'm thinking this about this correctly, the smaller the pulley used, the faster it spins in relation to engine RPM's, so the more load it puts on the engine trying to make the pump push fluid faster when the sticks are pushed forward. By simply using a larger pulley, you can gain torque but at the expense of speed for any given size pump/motor combo, and by using a larger pump instead while using an equal size pulley as on a smaller pump, you are basically doing the same thing as using the smaller pulley on the smaller pump by putting more load on the engine-correct?

[djagusch]

Originally Posted by Ridin' Green

Maybe you and puppy are saying the same thing, but I think you just shortened it, because this is what I always thought too. If I'm thinking this about this correctly, the smaller the pulley used, the faster it spins in relation to engine RPM's, so the more load it puts on the engine trying to make the pump push fluid faster when the sticks are pushed forward. By simply using a larger pulley, you can gain torque but at the expense of speed for any given size pump/motor combo, and by using a larger pump instead while using an equal size pulley as on a smaller pump, you are basically doing the same thing as using the smaller pulley on the smaller pump by putting more load on the engine-correct?

Your line of thinking is correct. Its the ratio of engine pulley to hydro pulley dia.
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[af73bn]

I get it now!
Thanks Puppy and everyone else, it makes sense now.
You are all very honorable grasshoppers!

[puppypaws]

The BDP-21L-408 is designed to run at 3600 rpms input maximum, and 1800 rpms minimum. 3600 rpms is also what your mower engines are calibrated to run so as to keep the hydraulics at maximum efficiency. The pulley sizes cannot vary on a vertical shaft engine, they must be a one to one direct link as with my Hustler Super Z. This is also the reason a vertical shaft engine puts more power to the blades (direct link) than a horizontal shaft engine, where the belt must be rerouted. No matter the belt configuration; even from a horizontal engine, there is no spinning faster or slower, the input shaft of the pump must get exactly 3600 rpms to operate as designed. This is also the reason air cooled components; be it an engine, or a mower's hydraulic system; must be run at the designed maximum rpm range to maintain their most effective cooling capability.

[djagusch]

Originally Posted by puppypaws

The BDP-21L-408 is designed to run at 3600 rpms input maximum, and 1800 rpms minimum. 3600 rpms is also what your mower engines are calibrated to run so as to keep the hydraulics at maximum efficiency. The pulley sizes cannot vary on a vertical shaft engine, they must be a one to one direct link as with my Hustler Super Z. This is also the reason a vertical shaft engine puts more power to the blades (direct link) than a horizontal shaft engine, where the belt must be rerouted. No matter the belt configuration; even from a horizontal engine, there is no spinning faster or slower, the input shaft of the pump must get exactly 3600 rpms to operate as designed. This is also the reason air cooled components; be it an engine, or a mower's hydraulic system; must be run at the designed maximum rpm range to maintain their most effective cooling capability.

Puppy, I know for a fact that pulley size is not 1 to 1 on one major mower line. The pulley size is used to make different top speeds. Pretty sure my math puts it at 2600 rpm which is right in the middle of max/min output. I also did the math on a another mower line and they had theirs at 3600 rpm. I don't think running them at max is the best for the life of them.
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[puppypaws]

Originally Posted by djagusch

Puppy, I know for a fact that pulley size is not 1 to 1 on one major mower line. The pulley size is used to make different top speeds. Pretty sure my math puts it at 2600 rpm which is right in the middle of max/min output. I also did the math on a another mower line and they had theirs at 3600 rpm. I don't think running them at max is the best for the life of them.
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I want argue the point that running them at their maximum input rpm may not be best for longevity. I just replaced both sides, pumps and wheel motors at 1100 hrs., and they ran every one of the 1100 hrs. at 3600.