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A hydrostatic tractor is one that uses a hydraulic drive propulsion system in place of a standard clutch and geared transmission. The hydrostatic transmission uses hydraulic fluid forced through a pump to drive the tractor. This fluid drive system is controlled by a foot pedal or a hand lever. The speed of the tractor is maintained by the amount of fluid the operator allows to flow through the system.
The initial cost of the hydrostatic tractor is typically greater than that of a comparably equipped standard transmission tractor. Many owners also experience higher maintenance costs due to the complex hydraulic drive system and its many filters and pumps. The efficiency of these tractors is also lower than that of a standard gear transmission with the hydro loss coming in the form of dissipated heat.
A benefit of the hydrostatic tractor lies in its ability to provide continually variable speeds without the need to clutch and shift gears. By simply moving the hand lever or pushing a foot pedal, the tractor's speed and torque can be adjusted on the fly. This allows the operator to vary the tractor's performance while not having to stop. By continuing to move forward or backward while adjusting to traction conditions, the tractor is less likely to become stuck.
The hydrostatic drive has been available in tractors for decades. It was first used in many heavy equipment applications, such as earth movers and bulldozers. This hydrostatic transmission has found its way into forklifts and even lawnmowers, based on its ease of operation in most cases. By implementing shift-on-the-fly technology, many jobs are completed faster by the use of a hydrostatic tractor.
Driving a hydrostatic tractor takes some getting used to. In high-torque situations, the operator must not apply more throttle to the tractor as would be common in a standard transmission application. By applying more throttle, the hydrostatic transmission will actually reduce the amount of available torque in its quest for added speed. To apply more torque and pull a heavy load easier, the operator must reduce the speed of the hydrostatic tractor. This will cause the tractor to pull harder and complete the task.
The hydrostatic drive has the ability to be infinitely variable in its gearing and will allow the operator to change speed and direction at will. Perhaps the easiest transmission to control, the hydrostatic drive is commonly referred to as the best transmission to use when mowing turf. The ease of operation and the ability to work for long periods without overheating make it a popular choice for many types of applications.
How common are these? Most tractors seem to be the typical ones driven by combustion engines, but perhaps hydrostatic tractors are gaining in popularity in some parts of the world.