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04-07-2003, 07:20 PM #1
- Join Date
- Sep 2005
Hi all, just wondering what the difference is between "Live" and "Independent" PTO's. Yeah, I'm a newbie . . .
04-07-2003, 08:22 PM #2
Re: PTO Types?
This has been discussed in detail before and now I can't find the old threads, but instead of me doing a lot of typing just go to this site and see if it doesn't answer your question well enough. Then if you still have questions, there are plenty of us on the forum who can answer them.
04-07-2003, 08:54 PM #3
- Join Date
- Sep 2005
Re: PTO Types?
The short version:
Many people interchange the terms, but:
Live means there are 2 clutches, one for the tranny, and one for the pto. You can keep the pto working & powered while changing tranny gears. Often the foot pedal is pushed down 1/2 way to stop the tranny clutch, and all the way to control the pto clutch. (Lot of Fords are like this.)
Independent means you have 2 clutches, but the pto clutch is controlled by a lever totally & independantly of the tranny clutch. You can shift either clutch at any time on or off, makes no difference what you are doing with the other clutch. Very often the tranny uses the foot pedal, and the pto is controlled by a bigger lever that moves the pto clutch.
04-07-2003, 10:59 PM #4
Re: PTO Types?
The site Bird posted is a pretty good site. A live PTO is where you can change the direction of the tractor or alternate the speed of it without changing the PTO. Any hydro transmissioin will give you that regardless of the type of clutch. My TC29D states that it has a Live PTO, but I still need to engage it with the clutch. I have the Hydro tranny.
Independent can have two clutch or only one. My neighbors John Deere he just engages the PTO with no clutch or anything.
But different styles can fall in the same terms.
04-07-2003, 11:57 PM #5
- Join Date
- Jul 2001
- Cooke County, Texas
- JD4320 with TNT, electric diverter, cruise control and air suspension seat.
Re: PTO Types?
This data is from www.tractorsmart.com:
Transmission Driven PTO. This is the simplest form of PTO design, in that it is driven (as the name implies) directly off a gear in the transmission. It is generally found in smaller, straight-shift tractors, which use a single clutch disc to transmit engine power to the drive train. The PTO is either fully OFF, or fully ON, as determined by the position of the PTO control lever. In order to select the ON position it is necessary to completely depress the clutch pedal, bringing all rotation of the transmission to a stop, before engaging the ON position. Re-engaging the clutch couples the engine back to the transmission, causing the PTO shaft to rotate, and also causing the tractor to move; if you have selected a gear other than neutral. This everything-happens-all-at-once type of PTO can be a nuisance, especially if you are working in close quarters with a rear mower or tiller. In the early days, this type PTO was the only game in town. As implements evolved, there arose a problem, in that the rotating mass of certain implements such as rotary cutters, with their heavy blades and blade carriers, had a tendency to push the tractor, even though the clutch was released. This was due to the momentum that had built up in the blades/blade carrier assembly. That momentum simply transferred its energy, via the PTO shaft, into the transmission, and back out of the transmission to the drive wheels of the tractor. That made for some exciting rides! (Many times through a fence, or over an embankment.) On older vintage tractors, this is a dangerous set-up. There is, however, a safety device, which is built-in on newer tractors, and available as an accessory for older tractors. This is known as the "over-running" clutch, or one-way clutch. Imagine that your PTO shaft is actually composed of a front, engine side (input) shaft, and a rear, implement side (output) shaft. The output shaft can only transmit power as long as the input shaft is driving it. As soon as you cease to impart a driving force to the output shaft, i.e. release the tractor's clutch, the output shaft is allowed to freely over-run the input shaft, thanks to the one-way clutch. In other words, this one-way transmission of PTO power makes it impossible for the implement to push the tractor. The engine/transmission can rotate the implement, but not vice-versa. If you want to know whether your tractor has this feature, place the PTO control lever in the ON position, stop the engine (put the key in your pocket) and with your hand, reach down and try to turn the PTO shaft in a clockwise direction. If you have a one-way clutch, you will be able to rotate the shaft, encountering only a slight resistance from the one-way clutch. Conversely, you should not be able to turn the shaft counter-clockwise (without also turning the engine).
Advantages of this type of PTO are simple design, low initial cost and less expense to maintain.
Disadvantages are the inability to fully control tractor direction and speed without disrupting implement power. In the case of a straight shift tractor with a mid mount mower deck that is driven by a mid PTO, you would be well advised to investigate thoroughly, the operational characteristics. You DO NOT want the mower to stop every time you change directions!
Live PTO. While still maintaining a relatively simple design, the usability of Live PTO is far ahead of the transmission driven variety. Nowadays, Live PTO refers more to operational characteristics than it does a configuration of specific parts. Huh? There was a time, not so long ago, that if you had a live PTO tractor, it meant that you had a dual clutch system. Dual clutch simply means that there are two clutch discs involved; one to engage/disengage the tractor's transmission, and one to engage/disengage the PTO. Depressing the clutch pedal approximately half way down would disengage the transmission clutch, while depressing it all the way down would also disengage the PTO clutch. This allows you to control the direction and speed of the tractor, without disturbing power to the implement. There is also the ability to feather the engagement of the PTO shaft, allowing a smooth start up of the implement before pulling out with the transmission. It only takes a few minutes in a tight field, with a mower mounted, to convince yourself that this is a much better set-up than the transmission driven PTO. This dual clutch arrangement is the most common, and best known style of live PTO. The advent of the hydrostatic transmission in recent years has given us another style of live PTO. While the parts list would more resemble that of transmission driven PTO, the functionality is the same as that of a dual clutch live PTO, in that tractor speed and direction can be variable, while PTO output remains constant.
Advantages are: relatively simple design, operator friendly in function, and safety. Safe, because, with the tractor movement and implement power dependent upon the position of the clutch pedal, you have a built-in panic button (the clutch pedal) that you can instantly depress to bring everything to a halt should things go awry.
Disadvantages are: more expensive to repair, extra routine adjustments (on dual clutches) to maintain proper operation, and a little more leg muscle is required to depress the clutch through both stages of the clutch.
Independent PTO. Available in two "flavors"; mechanical independent, and hydraulic independent.
Mechanical independent is essentially identical to a dual clutch live PTO, except that there is a separate hand lever to control the engage/release of the PTO clutch disc. Really, there are two controls for the PTO. In addition to the hand clutch lever, there is another lever that actually couples/uncouples the PTO shaft in the drive train. To start the PTO turning requires that you first move the hand clutch lever to disengage the PTO clutch. Then, you select the ON position with the PTO control lever. Next, using the hand clutch lever, you re-engage the PTO clutch, which causes the PTO shaft to begin rotating. One nice advantage of this system is that you can slowly, in a controlled manner, engage the PTO clutch, while the tractor is on the go. Disadvantages include having to fiddle with two control levers. Also there looms the potential for severe engine damage should you use this system incorrectly. Incorrectly means running around all day with the PTO hand clutch lever in the disengaged position, in order to stop rotation of the PTO shaft. Doing that puts a constant thrust load on the engine crankshaft, leading to accelerated wear of the crankshaft's thrust washers. The eventual result of this abuse is a ruined, non-rebuildable cylinder block. If you acquire a tractor with this type of independent PTO, please be sure that you are familiar with the correct operating procedures.
Hydraulic independent PTO is the most expensive, complex, and, in most cases, user friendly type available. Expensive and complex because operation depends upon various pumps, valves, filters, etc., all functioning correctly to drive the PTO shaft. User friendly, because one need only move a single lever, or push a button, to start/stop the PTO shaft. You are able to select ON and OFF, independently of tractor travel and speed. The heart of hydraulic independent PTO is the clutch pack. The clutch pack generally consist of several drive discs, and several driven discs. The drive disc stack is coupled to the engine side, so that any time the engine is running, these discs are rotating. The driven discs are coupled to the PTO shaft and will rotate only when the PTO is selected to the ON position. Rotation of the driven discs is achieved by directing pressurized oil behind a piston in the clutch pack, causing the piston to move into a position which squeezes all of the discs together, making them behave as a single unit. The drive discs were already turning, now the driven discs are turning as well, imparting rotation to the PTO shaft. Some form of PTO brake is incorporated into most hydraulic independent PTO systems. The function of the brake is to overcome the tendency of the PTO shaft to continue rotating, even when it is in the OFF position. This undesirable rotation is caused by oil drag between the drive and driven discs in the clutch pack. Without a brake, light load implements, such as hay rakes, might continue to slowly rotate, even with the PTO OFF. At best, this is a nuisance; at worst it could present a dangerous situation. PTO brakes are getting more reliable, however they are still subject to accelerated wear and damage, if continually called upon to stop heavy implements. A good example is the heavy duty rotary cutters that are popular today. There is a lot of potential energy built up in those heavy blades and stump jumpers when they are rotating at operating speed. When you select the PTO to the OFF position, your are disengaging the clutch pack, and redirecting the pressurized oil to the PTO brake system. Imagine trying to bring your truck to a stop from 50 MPH, using only half of the brake pads on one wheel, and you'll get the general idea. Some of these systems have an intermediate coast position between ON and OFF, which allows natural deceleration of the implement, saving wear and tear on the brake components. In the absence of that, you may wish to consider using an over-running coupler on the tractor PTO shaft, in order to avoid costly damage when using heavy implements.
Advantages are: ease of operation and maximum flexibility in determining when you want the PTO to be ON and OFF.
Disadvantages are: higher acquisition cost, more complex and difficult to troubleshoot/repair, higher maintenance expense and not quite as safe as live PTO. (If you needed to stop the PTO in a panic situation, can you find that little lever or button as quickly as you can "stomp" the clutch pedal all the way down?)
04-08-2003, 12:38 AM #6
- Join Date
- Sep 2005
Re: PTO Types?
Hey Froggy, Could you elaborate on that a little?
Just kidding - thank you all for the information. It is very helpful and much appreciated.