A better service truck specification starts by separating unnecessary idle from the engine hours that deliver compressed air, hydraulic power, and productive field work.
Fleets are right to question unnecessary idling. A recent article discussed the unplanned costs that a truck idling costs fleets money. An example of this might be when a truck is sitting in park for hours with its engine running only to maintain cab temperature, charging small electronics, or powering accessories, can quietly add fuel costs, engine hours, maintenance, emissions, noise, and wear. These costs are ones that fleet managers should be paying attention.
The U.S. Department of Energy’s Alternative Fuels Data Center notes that engines are idled for many reasons, including keeping vehicles warm or cool and powering emergency lighting, communications, or off-board equipment.
“Engines are idled for a variety of reasons, such as to keep vehicles warm or cool and to power emergency lighting, communications, or off-board equipment.”
That distinction is important because not all vehicle loads are equal. Keeping a cab comfortable while an operator completes paperwork is not the same as supplying continuous compressed air to a grinder, pavement breaker, or commercial tire service tool. A fleet may be able to turn the engine off for the first activity without affecting productivity. Turning the engine off during the second could stop the work entirely.
For utility fleets, public works departments, mobile mechanics, tire service trucks, heavy equipment repair teams, mining service vehicles, and other vocational operations, the truck represents more than transportation. It also serves as a mobile jobsite power platform.
When the vehicle engine is producing compressed air, operating hydraulic equipment, or helping a crew complete field work, the truck may be stationary, but it is not unproductive. That distinction should be understood before the next work truck, air compressor, battery system, or auxiliary power package is specified.
There is a significant difference between an engine running with no meaningful work demand and an engine operating as the power source for an air compressor, hydraulic crane, vacuum system, or other work equipment.
The U.S. Department of Energy’s guidance for medium-duty vehicles recognizes this reality.
“The idling episodes may be brief, or they might continue for hours, as in the case of utility trucks that need power to perform work.”
The goal should be to eliminate unnecessary engine operation without removing the productive power crews depend on. Even that statement requires some qualification. Fleets should not assume that every engine hour associated with a work function is automatically efficient. A truck may continue running at an unnecessarily high engine speed after a tool is released, or it may remain on when no equipment is being used. Poor controls and operating practices can still waste fuel during vocational work.
A properly specified vehicle-integrated system should therefore do more than provide enough power. It should also respond to actual demand, reduce unnecessary engine speed where possible, and make productive power available without forcing operators to manage a complicated collection of separate machines. Before choosing the power system, buyers need to ask better questions about the work.
The first question should not be, “How can we turn the truck off?” It should be, “What does the crew need to operate?” The answer needs to be specific. Saying that a truck requires compressed air is not enough. A technician using a 3/4-inch impact wrench intermittently has a different requirement than a crew operating a pavement breaker, horizontal grinder, or mobile tire inflation system.
The number and type of air tools establish the starting point for the entire compressed-air specification. A fleet should identify every pneumatic tool expected to be carried on the truck, including tools that are used less frequently but remain essential when the right job appears. It should then confirm the airflow and pressure requirements listed by each tool manufacturer. VMAC’s Air Tool Consumption Guide can help fleets estimate the airflow requirements of common pneumatic tools.
The final specification should reflect the actual tools, hoses, operating pressures, duty cycles, and field conditions involved. A compressor selected for an occasional impact wrench may not support continuous grinding. A system chosen for one small tool may also fall short when two operators need air at the same time. The buyer should be asking what the crew uses today, what it may use during the truck’s service life, and whether the compressor will continue to support those applications without forcing operators to wait.
Once the tools have been identified, the next question is how much compressed air they require. CFM, or cubic feet per minute, measures the volume of air a compressor delivers. Every pneumatic tool requires a certain amount of airflow at a specified pressure to perform as intended.
The compressor may technically operate the tool, but that does not mean it operates the tool productively. Buyers should calculate the combined airflow requirement of any tools that may operate simultaneously. They should also account for pressure losses caused by long hoses, small-diameter fittings, filters, regulators, and other components in the air system.
A compressor rated for the minimum required CFM may prevent a fleet from adding new tools later without replacing or supplementing the air system. The better question is not simply whether the compressor reaches the required CFM rating. It is whether it can sustain that output under the truck’s actual operating conditions.
This difference affects compressor sizing, cooling requirements, air storage, and duty cycle. A lower-duty-cycle compressor may be suitable for short, intermittent applications. The same compressor may become a serious productivity constraint when a tool runs continuously.
Duty cycle describes how long an air compressor can operate within a specified period before it must stop to cool or recover. A 100% duty cycle compressor is designed to continue producing air without scheduled rest periods. VMAC rotary screw air compressors operate at 100% duty cycle, allowing them to produce air continuously for sustained pneumatic applications. Instead of stopping the tool while a compressor cools or an air receiver tank refills, the operator can continue working.
This is where buyers need to examine field behaviour rather than relying only on a spec sheet. A tool may have a moderate CFM rating, but if it runs for most of a service call, the compressor must be capable of maintaining that airflow throughout the job. It is important to note that every single VMAC system operates at 100% duty cycle, which means you never have to wait for air and often also eliminates the need for an air receiver tank on many systems, reducing unnecessary bulk and weight.
This question follows naturally from tool runtime, but it deserves attention because it determines how much the fleet can rely on stored air. An air receiver tank stores compressed air and helps a system respond to short periods of high demand. For intermittent work, that stored capacity can be useful. The compressor refills the tank while the tool is not operating, preparing the system for the next short burst.
Continuous applications change the equation. Once the tank’s stored air has been used, the compressor must produce enough airflow to keep the tool running. If compressor output is below the tool’s sustained demand, pressure drops and work slows or stops.
A large tank can delay the problem, but it cannot correct an under-sized compressor. This is why buyers should not compare air systems based only on receiver-tank capacity. They need to compare continuous compressor output, operating pressure, duty cycle, recovery performance, and the actual airflow required by the tools.
The U.S. Department of Energy’s Work Truck Idling Reduction guide makes a useful distinction when discussing work trucks.
“The idling while the vehicle or equipment is not in use wastes fuel, causes engine wear, and generates noise and emissions.”
The key words are “not in use.” When a rotary screw air compressor is continuously supplying a productive tool, the engine is supporting work. When the tool is released and the air demand stops, an effective control system should reduce engine speed rather than continuing to operate at full output.
Cab heating, air conditioning, lighting, radios, computers, tablets, communications equipment, and battery charging may be good candidates for engine-off power.
The U.S. Environmental Protection Agency describes idle-reduction equipment as technology that provides services that would otherwise require operation of the main drive engine.
“Provides services that would otherwise require the operation of the main drive engine.”
For HVAC, lighting, electronics, and other relatively predictable loads, battery-supported systems, fuel-fired heaters, automatic stop-start equipment, and auxiliary electrical power can reduce engine operation without disrupting work. Equipment such as VMAC's G30+GEN Air Compressor/Generator, which combines continuous compressed air with 3,600 W of AC power, can also reduce the need for separate engine-driven equipment for technicians who require both air and electrical power. For applications requiring compressed air, hydraulics, welding, battery boosting, and generation from a single unit, VMAC Multifunction Power Systems allow operators to shut down the truck engine while still accessing up to six power sources on the job site. Compressed air and hydraulics, however, often place much greater and more variable demands on the truck than conventional electrical loads.
A battery system that performs well when supporting cab comfort may not be the right power source for continuous grinding, pavement breaking, high-volume tire inflation, or simultaneous crane and air-tool operation. This does not mean electrification is unsuitable for fleets, but it does mean that the power source must be matched to the load.
The buyer should separate comfort loads from workloads, calculate the power required by each, and then decide which functions can operate with the engine off and which require vehicle-engine power. Trying to manage every load through one idle-reduction strategy can lead to an expensive truck that reduces engine hours but also reduces jobsite capability.
Many service trucks require more than compressed air. A mechanics truck may use a hydraulic crane to lift a component while the technician operates a pneumatic impact wrench. A utility crew may need steady hydraulic power while using air tools nearby. Tire service, sign installation, heavy equipment repair, and infrastructure maintenance can all require compressed air and hydraulics during the same service call.
The important spec question is not only whether the truck needs hydraulics. It is whether hydraulic power and compressed air must be available simultaneously. If these loads operate at different times, separate controls or power systems may be acceptable. If the crane and air tools regularly operate together, the truck should be designed around that requirement from the beginning.
Adding hydraulic equipment after the air compressor has already been specified can create PTO conflicts, space problems, weight issues, plumbing complexity, and control-system limitations. This is where the VMAC DTM70-H becomes a strong vehicle-integrated choice.
The DTM70-H combines a direct-transmission mounted rotary screw air compressor with a hydraulic pump. It delivers up to 65 CFM at 100 psi and is available with hydraulic pump options ranging from 2.5 to 8 GPM. Both the air compressor and hydraulic pump can operate simultaneously through one PTO.
For fleets that require simultaneous air and hydraulic power, the better buying question is not which separate compressor and hydraulic package to purchase. It is whether one integrated multi-power system can perform both functions with less weight, less deck-space use, and fewer components.
Truck space has value. Every cubic foot occupied by an air compressor, engine, fuel tank, air receiver, or hydraulic reservoir is space that cannot be used for tool cabinets, hose reels, recovery equipment, welding equipment, replacement parts, or job materials.
A standalone machine may appear easier to specify because it arrives as a complete package. However, its effect on the rest of the truck should be considered before the purchase decision is made. Where will it be mounted? Will it interfere with compartment doors? Will it reduce visibility or access? Can technicians safely reach service points? Does it occupy space that could otherwise carry revenue-producing tools and inventory?
There is also the hitch to consider. A tow-behind compressor can provide substantial airflow, but it uses the truck’s towing capacity and may prevent the crew from pulling other equipment. It also adds another asset that must be registered, inspected, serviced, moved, secured, and tracked.
Weight should be reviewed as a complete-truck issue, not simply as an air-compressor specification. The truck must carry the service body, crane, tools, parts, fluids, fuel, operators, safety equipment, compressor and/or welder components, hydraulic reservoir, air receiver, hoses, and mounting hardware. A component that appears manageable by itself can contribute to an overweight truck once the entire build is complete.
Payload constraints can limit the tools and inventory carried to the job. They may also force a fleet to move to a larger and more expensive chassis. Vehicle-integrated rotary screw systems can reduce weight by using the truck engine as the power source rather than adding a second engine.
Depending on the UNDERHOOD model and the equipment it replaces, UNDERHOOD systems can reduce truck GVW by as much as 1,900 pounds. The DTM70-H has an approximate system weight of 180 pounds. By eliminating the need for a separate deck-mounted compressor and allowing smaller hydraulic reservoir requirements, it can free up as much as 600 pounds of available truck GVW compared with other configurations. Those weight reductions may allow the truck to carry additional tools, parts, equipment, or materials. They may also help preserve legal payload and reduce the temptation to specify a larger chassis simply to accommodate an inefficient equipment layout.
The buyer should ask whether payload is already tight and how every proposed power component affects the completed truck, not merely the chassis.
There is nothing inherently wrong with using separate equipment. In some applications, independent systems provide flexibility or allow components to be moved between vehicles. However, separate equipment also means separate mounting locations, controls, engines, batteries, fuel systems, maintenance schedules, service requirements, and potential failure points.
A standalone compressor with its own engine adds another oil supply, air filter, starter, battery, fuel system, cooling system, and scheduled maintenance program. A separate hydraulic power pack introduces additional plumbing and controls. An auxiliary generator adds another engine or electrical system. The buyer should ask whether those separate systems provide a meaningful operational advantage or simply add weight and complexity.
For fleets that only require compressed air, UNDERHOOD systems integrate the compressor into the engine compartment and use the vehicle engine as the power source. For fleets that want a PTO-driven air compressor mounted directly to the transmission, the DTM70 provides up to 70 CFM without occupying valuable deck space. For fleets that need simultaneous compressed air and hydraulic power, the DTM70-H combines both functions through one PTO-driven multi-power system.
This does not mean every truck should receive the same configuration. It means the fleet should decide whether it wants separate power equipment or one vehicle-integrated system designed around the truck’s real duty cycle.
What air tools are being used? How much CFM do they require? How long will they run? Is air needed continuously or only in short bursts? Does a hydraulic crane or other equipment need to operate at the same time? The buyer should then examine the truck.
How valuable is deck space? Is payload already constrained? Will a standalone compressor interfere with storage or require a larger chassis? Does the fleet want to maintain one integrated system or several separate power sources?
These questions naturally lead to vehicle-integrated air systems because they examine compressed air as part of the complete truck rather than as an accessory added after the major decisions have already been made. The right system is the one that delivers enough power for the work, responds efficiently to demand, preserves usable truck capacity, and allows the crew to complete jobs without waiting for air.
Idle reduction and jobsite productivity do not have to be competing goals. Fleets should reduce engine operation that serves no useful purpose. Battery-supported HVAC, automatic shutdown controls, lighting systems, telematics, operator training, and other idle-management technologies can lower fuel consumption and operating costs. However, a truck engine that is actively powering compressed air or hydraulic equipment is performing a productive function.
For pneumatic applications, UNDERHOOD and DTM70 systems integrate continuous-duty compressed air into the vehicle while protecting space and payload. For fleets that require both compressed air and hydraulic power, the DTM70-H combines those capabilities into one direct-transmission mounted system that can operate both functions simultaneously.
The best work truck specification is not the one that simply records the fewest stationary engine hours. It is the one that eliminates unnecessary idle, matches power output to actual demand, protects truck capacity, and gives the crew what it needs to complete the work.
The best system depends on the truck, air tools, required CFM, duty cycle, available deck space, payload, and whether hydraulic power is also needed. UNDERHOOD systems are well suited to fleets that need continuous compressed air in the 30 to 110 CFM range, while preserving deck space. The DTM70 provides up to 70 CFM through a direct-transmission mounted PTO system, while the DTM70-H combines up to 65 CFM with hydraulic power.
Different pneumatic tools have different CFM, pressure, and duty-cycle requirements. Identifying the tools first helps prevent the fleet from purchasing a compressor that cannot maintain adequate airflow during real work. Every pneumatic tool specifies how much CFM, or “Cubic Feet Per Minute” is required for proper operation; every air compressor specifies how much CFM it can produce. CFM represents the volume of air produced by your air compressor or required by your air tool.
We’re often asked if a particular air compressor installation requires an air receiver tank. The quick answer is most applications will benefit from air storage, even though it is not required for many rotary screw applications.
Air receiver tanks can be vertical or horizontal; tank choice is typically determined by the installation location, including the amount and shape of available space. Vertical air receiver tanks are readily available in sizes from 10 to 2,560 gallons, and horizontal receivers are available in 5 to 2,560 gallon capacities.
The DTM70 is a direct-transmission mounted PTO air compressor that provides up to 70 CFM. The DTM70-H combines an air compressor and hydraulic pump, allowing crews to operate air tools and hydraulic equipment simultaneously.