[AT] OT: hydrostat mowers( Hydraulic drive)

[Gene Dotson]

    Mowers do not use hydrostatic drive systems. They are hydraulic drives. 
Big difference in their design. Hydraulic drives use a constant displacement 
pump that always delivers the same volume of oil each revolution. The motor 
is also constant displacement and requires a set amount of oil during each 
revolution. Speed is controlled by the hydraulic drive system by controlling 
the amount of oil bypassed. More oil bypassed, the slower the speed and more 
heat from the bypassed oil, just like a stuck relief valve. in a hydraulic 
system. You will get maximum torque with the high speed setting with no 
bypassed oil.

    True hydrostatig like used in combines and large tractors use a variable 
output  pump and a variable displacement motor. They have maximum torque at 
the low speed setting as the pump output is reduced by shortening the stroke 
and the pump displacement per revolution is increased by increasing the 
length of piston stroke.

    There are certainly other systems that work on the same princilal.

    Link below may shed some light on the systems.

http://www.tpub.com/content/construction/14273/css/14273_221.htm

            Gene

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