Picking the Proper PTO

From transmission specs to the power needs of the driven equipment, here’s what you need to know to ensure you have the right PTO for your work truck.
Picking the Proper PTO

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The power take-off is what allows your pumper to be not just a truck, but also a profit-making tool for your business. Whatever equipment you need the truck’s engine to drive, the PTO can handle. But first, you need to be sure you have the right PTO.

Step one in making that selection is determining the make and model of the truck’s transmission, says Jeff King, marketing manager for PTO manufacturer Chelsea Products.

“Once you have that, you can see what openings and PTO rotations are available on that transmission,” he says.

The openings on the transmission play into where the PTO can be mounted.

“You might have two or three choices on a transmission, but that’s also dependent on what the truck manufacturer left for clearance or put in the way so you can’t use a certain opening,” King says. “What we’re seeing a lot now is the catalytic converter and everything else with the exhaust system is on the right-hand side blocking that opening. Depending on the transmission manufacturer, now you only have the left-hand side or the bottom opening to use for the PTO.”

Once you’ve narrowed down your PTO options to what will fit your truck’s transmission, you can start thinking about the equipment the PTO will be driving. One particularly key factor is the shaft rotation of the equipment. Make sure the PTO rotation matches; otherwise you might find yourself with equipment you can’t use.

“That’s one of the biggest things that gets overlooked,” King says. “People will buy the driven equipment first and they haven’t made sure they can get the correct rotation off the transmission and PTO combination. Understanding what rotations are available and then buying your driven equipment to match that rotation can save you some headaches. With some gear pumps, you can change the rotation. But for other types of equipment, you cannot and you have to order it with the correct rotation to begin with.”

Other considerations
Beyond the shaft rotation of the driven equipment, you’ll also need to know its other operating characteristics. Does it need to run at a high rpm with a lot of torque? Or will it be running at lower speeds? Once you know that, you can compare it against the optimal operating speed of the truck engine to determine what kind of performance you need out of the PTO.

For example, do you need to run a hydraulic pump at 1,000 rpm and want to run the truck engine at 900 rpm? Determine the PTO percentage by dividing the speed of the driven equipment by that of the engine. You figure out the proper torque rating by multiplying the horsepower of the driven equipment by the engineering constant of 5,252, then dividing it by rpm.

“In that case, you want something that is about 110 percent of engine speed,” King says. “With that, you go back to the list of PTOs that fit your specific make and model of transmission to see what is going to get you as close as possible to that 110 percent and what will give you the torque you need to power the equipment. That will help narrow the selection.”

When evaluating torque ratings, King says it’s important to keep in mind whether the driven equipment will be performing continuous- or intermittent-duty applications. A rating higher than the actual required torque will be necessary if the driven equipment is performing continuous duty.

“If it’s continuous — meaning more than five minutes of operation every 15 minutes — then you need to devalue the torque rating of the PTO by 30 percent,” he says. “One thing we’ve been doing lately on all our new PTOs is providing one single continuous-duty torque rating, so you no longer have to devalue the PTO. That’s on the automatic transmissions, so for the manual transmissions, the PTOs we’re designing still have the torque rating as an intermittent-duty cycle and you have to calculate the continuous-duty cycle.”

After you’ve ensured you have the correct PTO, you can focus on installation and maintenance.

“The PTO is going to last almost the life of the vehicle,” says King. “If you select it properly, install it properly, and do some good preventive maintenance, you’ll get your money’s worth out of it.”


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