Tractor PTO Shaft Types

Different examples of tractor PTO.

Some implements, such as wood chippers, rotary, and rakes, don’t generate their power. More often, you will need to transfer power to these implements to make them work. You need, for example, to attach the woodchipper to a tractor to power it. To transfer power, you need to use a PTO shaft. But what does PTO shaft mean? PTO, of course, stands for “power take-off.” 

Power take-off refers to the different methods of taking power from any power source. This power source can be a running engine. The engine’s power is then transmitted to the attached implement or separate machine.

The tool used to transfer this power is the “PTO shaft.” Its role is to transfer power to the attached implement. The PTO shaft has different parts. These parts include the external and internal PTO yoke and the universal joint. These parts also include the safety shield and safety chain.

If your tractor is equipped with PTO shaft, you can harness the full potential of your tractor. You can attach, for example, various implements to it to perform various tasks. One such implement that you can attached to the tractor is the rotary cutter. You need to engage the PTO to make the implement work. 

This process more often entails pushing the tractor’s clutch to the limit. You can do this while moving a lever to enable the PTO shaft to engage if the PTO shaft comes out of the tractor’s back. In some cases, you need to move a switch, lever, or a knob to engage the PTO. Once engaged, you can do whatever you want to do with the PTO. Once you’re done with whatever you want to do, you can then disengage the PTO shaft by doing the reverse-process.  

You can find in the market several PTO shaft types. So, you may get confused when looking for the right PTO shaft. Yet, you must get the right PTO for your equipment. Hence, you need to know the features and tips on how to zero in on the right PTO shaft.

1) Transmission PTO Shaft

The earliest form of PTO shaft is the transmission PTO shaft. You directly connect it to the vehicle’s transmission. This type of transmission comes with a main disadvantage—it stops moving once the tractor starts moving. Moreover, it becomes non-operational once the tractor goes out of gear. These two are drawbacks, especially when you are mowing. 

This is because the section you would like to mow will never be completely targeted. Hence, tractors—equipped with this PTO shaft—need a continuously running PTO shaft or an overrunning clutch. This PTO shaft can come in handy for preventing the PTO shaft from tagging or exerting too much pressure on the transmission. Too much tagging on the transmission can lead to the operator’s inability to stop the tractor.

PTO’s, attached directly to the transmission, can only engage once the transmission clutch is also engaged. But when you depress the clutch, you can’t drive the PTO. The clutch PTO prevents applying torque to the opposite direction. The transmission PTO is considered the earliest and simplest PTO type. Moreover, in the latest models of tractors, the overrunning clutch is a built-in accessory of the tractor. In older versions of tractors, however, you need to mount this equipment on the PTO shaft.

2) Two-stage Clutch (Live)

The live PTO functions using a two-stage clutch. You can control the PTO by pressing the clutch halfway. You can press the clutch fully to disengage the transmission. The upside of this type of PTO is that you can slow down the tractor while the PTO continues to operate. 

The live clutch lets the tractor’s transmission to operate on two modes. The PTO shaft, as said earlier, will continue to work even if the transmission is disengaged by simply pressing the clutch halfway. This removes the risk involved when you are switching gears. This is because the PTO shaft will no longer stop when you switch gears. Thus, your work is not interrupted when you switch gears.

The Live PTO utilizes a two-stages transmission clutch. The first stage allows you to operate the PTO shaft while you press the clutch halfway. The second stage, however, will enable you to control the PTO’s engagement. This basically separates the control of the transmission from the control of the PTO operation.

3) Independent PTO

The Independent PTO is a further innovation to the two-stage clutch PTO. You can activate this PTO even if you have stopped the tractor or if it is not moving. This means it is working independently from the transmission clutch. You can engage this PTO using a lever or a button which facilitates the controlling of the PTO. 

The good thing about the independent PTO shaft is that it is equipped with its clutch. This clutch is operated separately from the tractor’s transmission. The independent PTO also comes with two subtypes—mechanical and hydraulic. 

The mechanical type features a separate on/off selector. This on/off selector is distinct from the control lever of the PTO. The hydraulic type, however, comes with a single selector.  With the independent PTO at hand, you will have a perfect control of your tractor and the PTO.

You should remember that you don’t need to engage the clutch to make it operational when you are using an independent PTO. It is different from the live PTO wherein you need to fully press the pedal of the clutch to engage both the PTO and the transmission at the same time. Moreover, you will appreciate the use of the independent PTO, especially the hydraulic one, because it comes with hydraulic-independent clutches. You simply need to switch or turn a knob to make the PTO work.

Evolution and Standardization of the Tractor's PTO Shaft

The old and original type of PTO requires 540 revolutions/minute for its operation. This type, of course, had 6 splines. It also had a diameter of 13/8.” Soon after, two newer types came out that supported higher power applications. These newer types operated at 1000 RPM. They also had different shaft sizes. The larger shaft carried 20 splines with a diameter of 13/4″. The smaller one, on the other hand, had 21 splines with a diameter of 13/8″. 

All these three types exhibited a counterclockwise rotation if you were viewing their rotation from the tractor. Yet, if you were standing at the tractor’s back, the rotation might appear clockwise. The 10-spline type was first used in some early vehicles like the 1948 Land Rover. Moreover, a 6-spline adapter was supplied to make it workable. 

Manufacturers of agricultural machines usually indicate the nominal PTO power of the machines to indicate the shaft’s instantaneous power that is available. This is because older machines weren’t equipped with 540/540E or 1000/1000E choices. On the other hand, the latest models of tractors are equipped with the abovementioned options. Thus, with the newer tractors, you can power implements with low-power demand like those of the tedders or hay rakes. 

These low-power demand implements make use of lower engine speeds and less fuel and put decreased pressure on the tractor’s engine. Thus, the PTO and tractor’s efficiency are improved while reducing the costs of maintaining and running them. 

As a reference, the very first standard design for PTO was made in April 1927 and was adopted by the American Society of Agricultural Engineers. The rotation speed of the PTO was then set at 536 ± 10 rpm. This was later increased to 540 rpm.

Conclusion

PTO standards may vary from one region to another, and you will find less common and older PTO standards likewise. Moreover, some tractors come with power take-off that do not conform with the set standards. Thus, before you buy and tinker with a PTO, you should figure out first if the PTO you are about to use matches the implement. 

You should also remember that the size of the implement is critical to the type of shaft that you should choose. Any miscalculation in measurement may have an adverse effect on the tractor, implement, or shaft. This may also lead to damages to PTO shaft’s U-joints, tubing, and other parts of the shaft.

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