Hydrostatic taps only portion of engine total power for the wheels. Pulling/pushing capability is limited by design.
Relationship between displacement and torque of a hydraulic motor
T = D x PSI ÷ 24π
T is torque in foot-lbs; D is displacement in cubic inches per revolution; PSI is pressure difference across motor; π = 3.14
Horsepower for driving a pump
For every 1 HP of drive, the equivalent of 1 GPM @ 1500 PSI can be produced.
Many hydros do not have a relief valve. They rely on wheel spin as a pressure limiter.Hydraulic (fluid power) horsepower
HP = PSI x GPM ÷ 1714
PSI is gauge pressure in pounds per square inch; GPM is oil flow in gallons per minute
Great info, thanks!The Tuff Torq T40 in the JD LA115 is the precursor of the K46. By back tracking the math from the specced axle torque (171 ft-lb) through the gear reduction (28.04:1), the motor torque (73.18 in-lb) can be found. With the motor torque (73.18 in-lb) and motor displacement (0.0.61024 cu-in), the pressure (753 psi) can be found.
With a maximum rated input of 3400 rpm, a 0.4272 cu-in (7 cc) pump will flow 6.29 gpm.
Horsepower required (3.15 hp) = Flow (6.29 gpm) X Pressure (753 psi) / 1500
Horsepower available at the rear axle will be about 15-20% less.
Many hydros do not have a relief valve. They rely on wheel spin as a pressure limiter.
With hydraulics, there is always a loss of power transmission due to the need for clearances to lubricate the moving parts. As the pressure increases, so goes the loss due to the higher flow rate of pumped fluid through those clearances, hence the use of a Rule of Thumb with a divisor of 1500 for horsepower calculations rather than the more correct divisor if 1714 for theoretical calculations.
The transmission will perform to its maximum capability with a 5 hp engine, to allow for losses with the drive belt and charging system. The implements used on the tractor are where the large horsepower numbers are required.
There is only one hydro transmission used in GTs capable of surviving 3000 psi, the Sundstrand Series 15, which is used in mostly medium to heavy GTs.
Axle torque is what is used to get the load in motion and provide acceleration. Torque, in and of itself, does not imply motion. Horsepower is used to maintain the speed achieved by the torque. Applying 75 ft-lb of torque to a bolt torqued to 80 ft-lb does not result in motion.
I keep thinking about this. There could be one, a discrete one. Seen in YT videos, the motor is loosely pressed against the pump by its piston springs. If the pressure is too high exceeding combined piston spring rate, the fluid would push the motor casing away, breaking the fluid channel. Is it?Many hydros do not have a relief valve. They rely on wheel spin as a pressure limiter.
./////////////////////////////////////All that's good to know, but I was kinda wanting to hear from anybody with firsthand experience with a 300 series 10,12 or 14horse with both the hydro version and also one with the 8speed gear drive.
I've got a 314-8 that I use for hauling/pulling small cart for occasional yard clean up, and then annually pulling an aerator with a few hundred pounds of lead bricks. Would a 314-hydro be as capable ?
The hydros do not have hi-low. However they do share a similar rear end.thanks guy, this is what I was wanting to hear. It's about what I thought but wanted to hear from somebody who'd been there.
On the hydro units, is the rear axle heavy cast iron like the -8 units ? And do the hydro have hi/lo range