Information on the mechanization of agriculture, gardening, components and multifunctionality.

Tractor implement couplings, a safety issue

The high number of accidents due to careless maneuvers around cardan shafts transmitting the power of the tractor to implements. Special attention must be given to maintenance, the mechanical parts and the protection devices produced specifically by the manufacturing industries. Careful attention must also be directed to towing

by Davide Facchinetti
October 2015 | Back

The agricultural tractor is in fact a mobile power station, that is, on its own a machine which serves no purpose but provides power for a numerous series of implements coupled to it for performing a multitude of functions.

The power for various implements can be transmitted in a direct line by hooks or three-point hitches, through an hydraulic fluid flow under pressure coupled with designated hydraulic fixtures and/or by exploiting the vertical movement of the lift or in the form rotation drive coupled with the splined bars of the PTO through the cardan shaft.


Protection of cardan shafts 

This latter solution is the one most in use and the most troublesome also from the point of view of accidents. Considering fatal accidents of professional farmers and those caused by nonprofessionals such as those retired but still working or others involved in hobby farming activities, it is estimated that 30 to 50 deaths annually result from these accidents.

These accidents are rather violent and occur in fractions of a second with most of them starting with a limb or part of the victim’s clothing caught up by the unprotected section of the cardan transmission shaft. With the classic operation, the 540 rpm cardan shaft completes 9 rotations per second, which becomes 17 per second when the POT operates at 1000 rpm. In any case, with the engine running at a minimum regime the shaft completes 2 to 4 complete rotations in a second with extremely high torque in play to leave no time for anyone caught to react. 

These are accidents which often happen due to a lack of perception of the danger threshold, but most cases can be attributed to carelessness or the failure to carry out correct maintenance of the cardan shaft and its protection guard as well as the PTO shaft cone and the implement. This means that a cardan shaft transmission equipped with complete and effective protection can on its own guard against such carelessness as approaching the shaft in rotation resulting in tragedy in a few fractions of a second.

In addition to the serious and fatal accidents caused by cardan shafts in operation there are those assigned to stopped shafts occurring during coupling operation which, fortunately, almost always much less severe.

To ward off serious accidents it is almost always enough to make certain that transmission cardan shafts have the protection supplied by the manufacturer as standard equipment and offered as a replacement part. In any case, this very simple device must, however, meet strict type-approval regulations which the original manufacturer of the cardan shaft can provide.

Though these protection guards are easy to find, as are cones mounted on tractors and implements, but it is sad to note that they are not immediately replaced when deterioration is detected. It is sufficient to pay a visit to the manufacturer or have a talk with a public health unit inspector to become aware that this shortcoming as regards safety is the leading cause of sanctions applied by these inspectors.

Without getting into consideration of the unfortunate consequences resulting from these accidents, also economic, account must at least be taken for the verbal threats according to which new safety legislation is the equivalent of purchasing various dozens of PTO cones and cardan shaft protection guards and, though the purchase of protection is an investment in safety, the fine only marks the loss of resources.

A fixed guard must cover the cardan shaft by at least 50 cm to work properly according to the current regulations. The fact is that while for protection, the tractor itself may lack the rear part, almost always does, the implement must guarantee a 360° coverage by the cardan shaft guard and this thickness makes coupling very difficult, especially for opening the pawl which must be done while simultaneously pushing the shaft forward. Fortunately, recently put on the market are cardan shafts equipped with a device which keeps the pawl open so that the transmission shaft can be opened without the need to place the hand into a dangerous location. When the female sleeve abuts the lock the catch is released automatically.

It should be remembered that the maintenance of such critical safety parts and components must not be left to chance but performed scrupulously and with careful attention. Outside protection must be intact with no lacerations which can become dangerous at the coupling point, and the plastic sockets guarding again friction must facilitate the rotation of the shaft guard. If there is not a lock chain to block rotation equipped with a clip this is often a signal of alarm to indicate that the anti-friction sockets are no longer able to function correctly.

In summary, it is true that protection carries a cost but faced with the civil and penal consequences resulting from an accident there is no reason to be economic, just as a bit of care given to cardan shafts when they are not in use causes no harm. Though storage racks for shafts are obligatory, still frequently seen over the years on farms are cardan shafts abandoned in the open still mounted on their machines and possibly suspended in the air without their support chain.  


Couplings for towing      

There are also couplings for towing such as agricultural hooks, towing eyes and the drawbars mounted on implements which must be the manufacturer’s original equipment and in good shape. There are also critical safety devices which must come through special testing for compliance with type-approval. These components are stamped, or show in relief, the manufacturer’s code and are subjected to the most severe type-approval procedure. Also the mounting pin must be original equipment with its own retainer plugs which have not been replaced in a mechanics shop with those made in low quality steel.

Hooks which can be regulated for height or on a horizontal plane must be checked periodically to make certain they function smoothly and without excess force and to apply lubricants to the moving parts when necessary.

Care must also be taken to avoid excessive play between the pintle and the eye coupling which can lead to rapid wear and possible breakage. On the other hand, if the lock chain is not in use the pin plug can can come unscrewed as the result of bouncing to lead to serious consequences. Moreover, when the pintle shows wear or is battered and out of shape it must be immediately replaced with an original spare part.

For mounted and semi-mounted implements, those connected by the tractor three-point hitch, the hitch must be integral and not out of shape, bent or rusted and must be equipped with the prescribed lock chain.


Hydraulic and pneumatic plant

Hot fluids under pressure as is hydraulic oil, or the use of compressed air, can become a sources of danger in case of an explosive break in the hose, connector or tank causing the fluid under great pressure with great kinetic energy and parts or metal components to strike the operator.

This means that hydraulic and pneumatic plant for agricultural machinery and all their components must be fully efficient and integral. The connectors and tubing of new   systems in production must report information on the manufacturer, the date of construction and the pressure values for operations and approaching explosion.

Whenever connections or tubing show evident signs of aging, wrinkling or cuts, or mechanical damage such as loosing shape or flattening, they must be replaced immediately with original spare parts.

Hydraulic outlets connected to outside circuits must be integral and not show loss of oil, drawn out or dipping, and for operations for mounting or removing tubing the body of the plant must be securely anchored to the machine.

Moreover, a compressed air tank but be equipped with a manometer which shows the inside pressure to allow the operator to check and use and maintenance manual to verify whether the pressure displayed by the meter is in line with recommended pressure. If anomalies or doubts about whether the compressor is working properly turn up, qualified personnel must be called on immediately to check and, if necessary, repair the unit. These recommendations are of great importance because most accidents caused by hydraulic or pneumatic system happen suddenly and can cause unforeseen consequences with no advance warning. 


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