Th ere are many reasons why it is important to specify and order the correct PTO for the intended application, and then to have it properly installed and maintained. Key among these is to have: • A lengthy, productive lifecycle with optimal operation. • No, or minimal, downtime. • Lower overall cost. NEED TO KNOW Here is a best practice for analyzing any PTO application: 1.Note the make and model of the transmission that will get a PTO. Th e reason being: a PTO essentially serves as an extension of a vehicle’s transmission and transmits its power to the output shaft . Th e transmission’s make and model number can be found on the manufacturer’s tag on the transmission itself. With a new vehicle, this is on the build sheet. Be sure to note any model prefi xes or suffi xes. Th e local truck dealer also may be able to identify the transmission through the Vehicle Identifi cation Number (VIN). 2. What type of equipment is to be driven by the PTO? 3. What is the input horsepower required by this equipment? A PTO’s horsepower is directly proportional to the output shaft rpm. Th erefore, the faster it turns, the more horsepower is produced. Th e formula to determine the horsepower (hp) is: hp = torque (T) x rpm ÷ 5,252. PTOs are typically rated according to torque capacity. In simplest terms, torque is that amount of force needed to make something move or run. Torque is directly related to horsepower and rpm. Be advised, a PTO’s torque rating is constant, regardless of how fast the output shaft is turning. Torque is the limiting factor. If torque loads are too large for too long, the PTO can be damaged. Th e formula to calculate torque is: T = hp x 5,252 ÷ rpm. Pumps, like most other PTO-driven equipment, require a fi xed amount of horsepower and input speed (rpm) to produce a required fl ow of fl uid measured in gallons per minute (gpm). Th e formula for this is: Pump input hp = gpm x psi ÷ 1,714 ÷ pump effi ciency. 4. Determine the desired input speed of the driven equipment. 5.Determine engine the approximate speed desired during operation of the equipment. THE PTO needs to meet performance requirements of the auxiliary equipment. Th is speed can increase, decrease or directly transfer the speed needed to move the equipment to be driven by the PTO. As such, the relationship is fi gured as a percentage of the desired engine speed during the PTO duty cycle. Th e formula to use is: Equipment speed ÷ engine speed = PTO speed. By way of example, if the required speed for a pump is 1,000 rpm and the engine operating speed is 1,500 rpm, the percentage of PTO speed to engine speed is approximately two-thirds, or about 67 percent. Conversely, if a pump requires 1,500 rpm and the desired engine operating speed is 1,000 rpm, the PTO will need to be rated at approximately 150 percent of engine speed. 6.Determine the PTO direction of rotation of the device being driven in relation to direction of engine rotation. Th ere are two directions: • Engine – Th e driven equipment rotates clockwise (righthand rotation). • Opposite the engine – Th e driven equipment rotates counterclockwise (left -hand rotation.) A geared adapter, which adds a gear set, can be used to change the rotation. Another alternative is to use a PTO that has forward and reverse gears. When considering a PTO’s direction of rotation, spec the PTO looking from the rear of the truck to Medium Duty | the front of the truck. Th e driven equipment is spec’d looking from the front of the truck to the rear of the truck. 7.What will be the type of connection between PTO and the driven equipment: driveshaft (remote) or direct mount pump fl ange? 8. Where will the PTO be mounted on the transmission: left , right, top, bottom or countershaft ? 9. Will the PTO duty cycle be intermittent or continuous? Intermittent duty cycles are considered those that last for less than fi ve minutes at a time, a few times a day. For intermittent operations, the torque requirements of the driven equipment can be determined using this formula: T = hp x 5,252 ÷ PTO output rpm. Continuous duty applications reduce the PTO’s torque and horsepower ratings. If these are miscalculated, the lifespan of the PTO will be less than expected. If the torque requirements are continuous – more than fi ve minutes operation every 15 minutes, multiply the torque fi gure by 0.7. Th e result will be the torque required for continuous operation. 10.Determine if the PTO will need speeds or reverse gear requirements. 11.What is the method by which the PTO will be engaged? PTOs can be engaged by means of a cable, air pressure, electric solenoid or hydraulic pressure. Properly specifi ed and installed, PTOs require little maintenance. Check the PTO periodically for evidence of oil seal wear and loose or misadjusted shift ing linkage. If a hydraulic pump is direct coupled to the PTO, it should be removed every 90 to 180 days, depending on frequency of use, and the spline coupling re-greased. Never hesitate to contact a truck dealer, OEM or PTO supplier for assistance with selecting and properly maintaining a PTO. Contributing to this article were: Dave Douglass, director of training and education, Muncie Power Products (www. munciepower.com), a leading manufacturer of power take-offs, hydraulic components – such as pumps, motors, cylinders, valves and reservoirs – and snow and ice removal products. Jeff King, marketing manager, Chelsea Products Division of Parker Hannifin (www.parker.com), a leading global diversified manufacturer of motion and control technologies and systems. Chelsea is a global innovation leader in power take-off technologies. PTOs that have a compact housing and come with various assembly arrangements, for example the Chelsea 870 Series, help eliminate clearance issues and maximize installation possibilities. Photo courtesy of Chelsea Products Division PTO safety Chelsea Products Division offers these power take-off safety instructions. GENERAL SAFETY To prevent injury and/or damage to the equipment: • Carefully read all owner’s manuals, service manuals and/or other instructions. • Always follow proper procedures and use proper tools and safety equipment. • Be sure to receive proper training. • Never work alone while under a vehicle or while repairing or maintaining equipment. • Always use proper components in applications for which they are approved. • Be sure to assemble components properly. • Never use worn out or damaged components. • Always block any raised or moving device that may injure a person working on or under a vehicle. • Never operate the controls of the PTO or other driven equipment from any position that could result in getting caught in moving machinery. SHAFT ROTATION The PTO output shaft rotation could cause unexpected movement of the driven equipment, resulting in serious personal injury, death or equipment damage. To avoid this possibility: • Driven equipment must have separate controls. • The driven equipment must be left in the disengaged position when not in operation. • Do not operate the driven equipment until the vehicle is allowed to warm up. DRIVESHAFTS Rotating auxiliary driveshafts are dangerous as they can snag clothes, skin, hair, hands, etc., and this can cause serious injury or death. To avoid this risk: • Do not go under the vehicle when the engine is running. • Do not work on or near an exposed shaft when the engine is running. • Shut off the engine before working on the PTO or driven equipment. • Exposed rotating driveshafts must be guarded. VehicleServicePros.com ❚ JUNE 2016 ❚ FLEET MAINTENANCE 23
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