For commercial truckers, power take-offs get real results. In one recent experiment, a fleet of 150 bucket trucks saved $443,000 in fuel costs and slashed CO₂ emissions by 788 tons in a single year—just by integrating electrical power take-offs (ePTOs).
Moreover, though ePTOs are the newest, trendiest devices on the block, old-school PTOs are still incredibly useful.
In the average vehicle with a typical, gasoline-fueled combustion engine, only 12%–30% of the energy it takes is used to power the driveline. The majority of the energy granted by the fuel is lost, inadvertently converted to unusable thermal energy.
The “excess” heat then dissipates, off-gassing as hot air from the engine, through exhaust pipes, or into the ground via the wheels (as friction heat).
Even the lowest-tech power take-offs stem this loss. PTOs capture a percentage of the energy output from a vehicle’s engine, transmission, or battery, then redirect it to a useful task: powering auxiliary equipment.
In this guide, learn how different types of PTOs work, their benefits and drawbacks, and how to choose and maintain the right PTO for your commercial HDV.
Power Take-Offs, Defined: PTO Function In Heavy-Duty Trucks
PTOs are energy redirection and conversion devices, built to integrate into a machine’s powertrain. They’re used in industrial machinery in manufacturing facilities, drivable agricultural machines like tractors, and vehicles—particularly Class 7 and Class 8 commercial trucks.
What Is a Power Take-Off In Machinery?
A power take-off is an assembly: a device composed of smaller components, working together to serve its function. The specific functions of a PTO are energy conservation, conversion, and direction.
WhatIs?, the technology resource guide by TechTarget, has a useful description. It defines “Power take-off (PTO)” as “a device that transfers an engine's mechanical power to another piece of equipment.”
Typically, only a portion of the engine’s energy output is transferred to the PTO’s recipient machinery.
The guide then explains, “A PTO allows the hosting energy source to transmit power to additional equipment that does not have its own engine or motor. For example, a PTO can help run a jackhammer using a tractor's engine."
In essence, a PTO is an assembly, like a gearbox, that enables an engine or motor to power more machines or systems than it otherwise could.
Unique Function of PTOs In HDV Drivetrains
When they’re integrated into commercial, heavy-duty vehicle powertrains, PTOs are used to power auxiliary equipment integrated in the HDV.
Auxiliary equipment is any functional, mechanical parts of a vehicle unrelated to driving, yet typically necessary for the HDV to serve its function. Thus, for commercial HDVs, a PTO can effectively empower:
Open-box beds of dump trucks
Tow truck winches (automatic cables)
Hydraulic pumps and lifts for construction attachments
Vacuums
Rotating mixer drums on cement or concrete trucks
Electrical generators for refrigeration units (cold transport)
Snow plow machinery
Sprayers, rotary brooms, and hoppers on street sweeper trucks
With a power take-off, each of these mechanical add-ons can function effectively, solely using energy sources already built into the truck—its engine, transmission, or battery.
How Does A PTO Work In A Heavy-Duty Truck?
In a heavy-duty truck, a PTO redirects power from either the truck’s engine, transmission, or battery, to auxiliary equipment or machinery.
Different PTOs use distinct energy transfer mechanisms. To receive and route the energy, most PTOs use one of four mechanisms:
Physical, rotational mechanisms (i.e. non-synchronous gearbox components), which redirect the mechanical energy without converting it.
Hydraulic mechanisms, which convert mechanical energy into hydrostatic energy before transferring it.
Electromagnetic induction mechanisms, specific to PTOs that convert mechanical energy into electricity (like a generator).
Electrical conversion and transmission mechanisms, which invert and transform the electrical output from a truck's battery or an EV's motor into a usable A/C current, then use that current to power equipment.
Only electrical power take-off (ePTO) devices use electrical conversion.
Differentiating Power Take-Offs: Types & Categories
Short Duration Vs. Continuous Operation
Some PTOs are designed to continually deliver energy to the equipment as long as the commercial truck is running. Others engage and disengage independently of the HDV’s engine, only delivering energy to equipment when activated.
Short-Duration PTOs (Independent / Intermittent)
Short-duration power take-offs, also called independent PTOs, are not engaged at all times. Instead, they can be engaged and disengaged as needed, either manually (by the vehicle’s operator), or automatically in response to operating/use conditions. They’re sub-categorized by the type of shift used to engage or disengage the device, with two-stage clutch mechanisms among the most popular independent PTOs.
These devices are designed to transfer power to auxiliary equipment in short increments. Typically, short-duration PTOs deliver bursts of energy for five minutes or fewer in a 15-minute span.
If energy is meant to be routed in a predictable pattern of short bursts, the device might be called an intermittent PTO. Tow trucks, dump trucks, and truck-mounted aerial work platforms are more likely to use an independent PTO.
Continuous PTOs (Live / Constant Drive)
Continuous PTOs, also called “constant drive” or “no-clutch” power take-offs, are always engaged. Their function is wholly aligned with the vehicle’s engine. If the truck is on, so is the PTO.
These devices are best for powering equipment for extended periods, and they're all but necessary for non-stop applications. Constant drive PTOs are best for street sweepers, snow plows, garbage trucks, and similarly utilitarian HDVs.
PTO Shift Types
Power take-offs can be categorized by shift type. Most PTOs are mechanical (manual) shifts, which use a lever or compressed air mechanism to physically shift gears in the PTO's non-synchronous gearbox.
Other PTOs are clutch shifts (also called “power shifts” or “hot shifts”). Clutch shifts are semi-automated, and they’re used in short-duration applications.
More rare are non-shifting, constant drive PTOs. These power take-offs constantly feed power from the engine to auxiliary machinery, even when the HDV isn't in motion.
PTO Engagement Mechanism Categories
PTO engagement is the feature or mechanism that activates the power take-off, initiating its energy transfer. Among PTOs used in commercial vehicles, four engagement mechanisms are common.
Mechanical (Lever Or Switch) Activation
Mechanical PTOs utilize diverse engagement components, including sliding gears and mesh, rubber blocks, loaded springs, a manually operated lever or pedal, or mechanical cable links.
Hydraulic / Hydrostatic Pressure Mechanisms
Hydraulic features apply pressure to the device’s control valve, engaging the clutch. Once engaged, the clutch connects the PTO shaft to the engine.