A tractor is used for not only pulling the implements for tillage operations and sowing of various crops but also used to power stationery and moving equipment for doing operations such as threshing of crops, pumping water from tube-wells, spraying, rotavator and others. A power outlet is generally provided at the rear of the tractors. The power outlet is known as Power Take Off (PTO). PTO was first introduced by International Harvester Company in 1918. In India, the PTO is usually on the rear side, but in developed countries, a front PTO is also an option for powering front-mounted attachments.
Power to the PTO shaft comes from the gearbox. The countershaft of the gearbox is usually extended out to the rear side to act as the PTO outlet.
Standardization of the speed of the PTO is important so that the equipment can be designed around the given speed. For example, the threshers are supposed to run at a particular peripheral velocity of the threshing cylinder. The pulley arrangements are made with the standard PTO speed in mind.
Prior to 1958, the standard PTO speed was 536 rpm. Later this speed was changed to 540 rpm and another speed was added to the standards i.e. 1000 rpm. The splines provided over the PTO out shaft is also different for avoiding accidental attachment of implement of the different speed setting. In case of 540 rpm, the shaft has 6 splines, while for the 1000 rpm shaft, the number of splines is 21. If a PTO can run on both 540 rpm and 1000 rpm speeds then it is known as Dual PTO.
Types of PTO are available in India
Economy PTO (EPTO)
This feature allows the operator to run the PTO at 540 rpm, but at a lower engine rpm than the standard, PTO rated speed. Economy PTO allows the tractor to operate at the required 540 rpm at the PTO but with lower engine rpm, which saves fuel, reduces vibration, and reduces noise. 540 economy is ideal for many applications including mowing, baling, or tilling. The 540 economy setting cannot be used with full advertised PTO horsepower (hp). If full PTO hp is required, the tractor should be run in standard 540 modes.
Live PTO (LPTO)
A live PTO, normally, has a 2 stage clutch. You can depress the clutch 1/2 way in and the transmission will stop but the PTO will continue to spin under a load (not just free spin). If you depress the clutch all the way the PTO will stop also. This is very useful when mowing because you can stop, change gears, back up, etc while the mower continues to receive power.
If the PTO is not "live" it will stop receiving power every time the clutch pedal is depressed. Because the PTO is always directly connected to the transmission you will need an over run clutch if you use a high momentum implement like a mower.
Independent PTO (IPTO)
An Independent PTO is controlled by an electric switch. You can turn the PTO on and off using the switch and the position of the clutch pedal has no effect on the PTO.
Reverse PTO (RPTO)
A Reverse PTO can turn in the reverse direction through a lever or button. This is essential when operating implements which can get stuck such as post hole digger and thresher.
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