One of the things at which our team at Southwest Products excels is making recommendations for work trucks with onboard air. We recently came across an article from For Construction Pros that hit a lot of good points about selecting onboard air compressors. Here are some of the highlights.
The first things to determine are the basic operating conditions for onboard air. Primarily, how much pressure (psi) and flow (cfm) is required for regular tasks? Also, what is the duty cycle for which it will be used?
Evaluate the tools used on a regular basis to determine the power requirements. Air flow is obviously the top requirement. If multiple tools will be used simultaneously, add their cfm together to account for the dual operation. Most tools require 90 or 100 psi, though some may require 150 to 200 psi.
Once the flow and pressure requirements are determined, make sure the truck or PTO can handle the load. The more flow and pressure you need, the more horsepower you will need.
The power requirements for your setup will also help determine the best compressor drive option.
- In 100 – 200 cfm range, the up-front cost of an engine driven compressor is significantly more than a PTO-driven compressor.
- In the 20 – 90 cfm range, look to how the truck is equipped. Does the truck already utilize hydraulics, or is it equipped with a PTO port for an hydraulic system? If it does not, then an engine-driven compressor is the right choice.
- High-demand air applications still favor a PTO drive. If the application requires more than 25 hp, the under-deck PTO drive is the right choice, and are typically Rotary Screw designs capable of delivering 90 to 220 cfm of air.
- Under-deck air compressors typically operate large pneumatic tools like jackhammers, rock drills, and underground boring equipment.
- Make sure to understand what continuous-duty torque limitations exist, or how to order the truck so the under-body unit will fit properly. Fuel tanks, exhaust, brakes, cab-to-axle, wheelbase, cab type, and potential relocation of DEF tanks or 4×4 transfer cases may be impacted by the chosen compressor unit.
- Trucks can be factory-equipped with connections to the engine and transmission control modules to improve quality of compressor installation.
- Engine-driven above-deck compressors save wear and tear on the truck’s engine and transmission, and installation is fairly simple: they can be bolted to the truck bed, have an air line run to the filter/regulator and they are ready to be used.
- Diesel and gas options are both available, and it might make sense to choose the same fuel type as the chassis.
Reciprocating vs. Rotary Screw
The most common compressor configurations are Rotary Screw and Reciprocating. Reciprocating compressors come in single and two-stage options. The main difference is that two-stage compressors will keep up better with constant demand, such as from an impact wrench, and generally offers pressures between 100 – 250 psi. Single-stage compressors can be chosen for less demanding applications, at 70 – 100 psi.
Rotary Screw compressors provide high volumes of high-pressure air at a continuous duty cycle for high-power air tools, such as jackhammers. They are a relatively simple design with no valves, and provide instant air on demand, but require very high rotor speeds. Although they don’t require a reservoir tank, it can be a good idea to help dissipate heat and remove moisture from the air.
Aside from the type of tools being used, the biggest consideration between Reciprocating or Rotary should be the long-term cost. Although Reciprocating compressors can have a lower up-front cost, Rotary compressors provide performance that can decrease job costs, which may provide a better investment in the long run.
Choosing the Best Placement
When it comes to positioning, above-deck compressors are the most popular for mechanic’s trucks due to available space on the side pack. However, when a lot of air is required and two PTO units can be run, or if only an air compressor is needed and no other PTO-driven equipment is run, an under-body air compressor might be the right choice.
Under-hood compressors are a good option when there are space constraints on the truck’s transmission, in the truck bed, or if using a van body for the work truck platform. Other location considerations include weight limitations, available power sources (including PTO and/or hydraulics), or amount of air required. Applications are also a critical consideration, including what other equipment may be needed on the jobsite: perhaps a crane, welder, generator, booster, etc., which may also require power or space.
Avoiding Common Mistakes
As touched on previously, under-sizing to save up-front cost is a common mistake. If the application requires more air flow than what the compressor can efficiently produce, it leads to increased duty cycles and premature wear on compressor components, requiring in a shorter lifespan.
On the other hand, a compressor might be chosen that requires more activity than the application requires. For example, Rotary Screw compressors work best when allowed to run for more than 15 minutes at operating temperature, allowing the moisture to evaporate out of the oil in the compressor, which saves on maintenance requirements. If Rotary Screw compressors will be operated only periodically, a Reciprocating compressor would be best.
Another problem is making a purchase based only on what may have been used in the past. Due to advancements in technology, there are many new options that may be a better fit. Take the time to analyze all applications and the work environment, including talking with the operators and learning about their challenges, requirements, and true usage of the truck and air compressor. One of the things you might discover if you are considering purchasing a unit that has its own power so the truck does not have to idle, is perhaps the operator would end up running the truck because they need to keep the cab heated in winter or cooled in summer, anyway, in which case, you may as well use the vehicle power for operation.
As this article demonstrates, there are many considerations in choosing onboard air for work trucks. Although this article gives quite a bit of insight, you may have additional questions, which we would be happy to answer. We are also happy to provide custom recommendations and truck configurations.
Southwest Products Team
Our team are industry experts with more than 50 years of experience building customized trucks for some of the industry’s largest companies. Using 3D designs and an extensive portfolio of past projects, our customers can visualize exactly what their truck will look like before any work is done. There is no other manufacturer that compares with our capabilities and service. Contact us to start a discussion about your mechanics truck needs.