Matching Generators and Compressors With Your Job Site

Adhering to a blueprint of key factors will help contractors choose the best compressor or generator for a job site.

When it comes to compressors, consider rated capacities, fuel consumption, emissions requirements, operating costs, and service costs.

Considerations for a generator include how it will be used, power requirements, load size, equipment proximity, fuel requirements, and ease of operation. Whether the generator is needed for a custom or turnkey job is another factor.

It’s important to size equipment specific to the job, notes Jeremy Bailey, product manager for air compressors for Doosan.

Consider the cost of ownership when contemplating long-term use and fuel costs and maintenance in both short-term and long-term use, notes Bailey.

“Look at what machine is going to get you the most fuel economy,” he says.

One of Doosan’s most popular air compressors is the P425/HP375WCU-T4F unit with a dual pressure/dual flow feature.

“The ‘two machines in one’ feature has benefits for the end-users and rental yards that may stock these machines,” notes Bailey, adding that Doosan offers that feature in its P250/HP185, P425/HP375, and XP825/HP750 T4F machines.

While contractors previously would have to buy or rent two separate machines for power and flow, newer technology enables them to have “two machines in one with the push of a button, allowing the contractor to adjust both pressure and flow,” says Bailey. That also takes up less space at a job site or rental yard, he adds.

“When selecting a piece of equipment, consider the acquisition costs and also consider the cost of the life of that machine,” says Bailey. “It adds all together for total costs.” Bailey notes that the machines hold trade-in and resale value.

With air compressors, a contractor also can opt to buy two small units to use together for big jobs or if a job is small, then only one is needed onsite, he says.

Contractors concerned about getting “trapped” into a piece of equipment have options as their business expands, says Bailey.

The versatility built into the P425/HP375, for example, is designed to offer contractors increased productivity and lower cost of ownership. The unit features a galvanized steel enclosure, an A-frame drawbar, and heavy-duty axles. A thermostatic clutch-driven cooling fan is designed to ensure quiet operation and cut fuel costs by an average of 10% in cold weather conditions. A Doosan airend is designed to offer an optimally efficient rotor profile that requires less horsepower for high-volume cubic foot per minute (CFM) output. The unit is powered by a Cummins QSB4.5 engine.

Knowing air consumption requirements to determine CFM output and pressure is key to choosing the best air compressor for a job, concurs Ralph Kokot, the chief executive officer at Vanair Manufacturing.

A 90-pound pavement breaker takes about 68 to 80 CFM to run depending on its age and seal wear and tear, he points out. Running multiple pavement breakers off of the same machine requires higher CFM output and pressure, he adds.

Duty cycle also is important, particularly in some of the larger machines with horsepower reductions associated with duty cycles, he notes.

Focusing on a preventative maintenance schedule is important, Kokot says.

“Rotary screw compressors are precision pieces of equipment,” he says. “They run at very high rpm and very tight tolerances, so maintaining them properly would certainly increase their longevity.”

Kokot says he knows of some companies that have compressors on a second or third chassis. “They could be 30 years old and they’re still running fine,” he says.

The rated compacity of an air compressor will ensure its highest efficiency, notes Eric Massinon, business development director at Chicago Pneumatic.

“Does the compressor produce enough air at the right pressure for the air tools used or other applications? Many compressors are rated at a higher CFM than they actually produce,” says Massinon.

“When purchasing or renting, ask if the compressors meet the International Organization for Standardization’s test criteria, the ISO 1217:2009 Displacement Compressors–Acceptance tests. This standard ensures you are getting the volume you are paying for.”

Massinon concurs that operating costs, service costs, and fuel consumption also are key factors.

The newest technology requirement for the compressors is the emissions requirements for Tier 4 Final (T4F), Massinon points out.

“The T4F emissions requirements have driven up the prices on compressors substantially in the last two years,” he says. “The increase in the prices has many customers re-evaluating what size compressor they actually need.”

Twenty years ago, the rental industry operated with two different lines for compressors: a single-tool and a two-tool line, notes Massinon.

“The single-tool compressors rated at around 100 CFM and the two-tool compressors rated at around 185 CFM. These size ratings were based on the typical air consumption from the 90-pound pavement breaker, with each tool using an average of 85 CFM,” he points out. “Single-tool compressors and two-tool compressors is how the rental industry referred to the different sizes.

“The industry changed when the price of the single-tool compressors became comparable to the price of two-tool compressors,” adds Massinon. “From that point on, the industry shifted to a 185 CFM compressor. This shift has remained for over 20 years because the average price difference was less than $1,000 and there were no operational issues in using a single-tool with a two-tool compressor.”

Twenty years later, the price difference is closer to an average of $5,000 and rental companies and contractors are evaluating much more carefully what they really need for air consumption on the job, he says, adding that there is currently a push for creating a single-tool compressor market once again.

Ultimately, compressors, air tools, and applications for air compressors can be better served with the right size compressors in addition to the options and accessories needed by the tools, says Massinon.

“Contractors should consult with the manufacturers and dealers for suggestions on their specific requirements,” he adds.

When evaluating air compressors for its fleet, United Rentals looks at features, benefits, and manufacturer specifications such as CFM output and fuel consumption per hour, notes Brent Kuchynka, vice president, corporate fleet management.

United Rentals field-tests units first to ensure that the product is as efficient as the manufacturer has claimed, notes Kuchynka.

“Once the model is in our fleet, we gain data quickly about uptime histories, repair costs, warranties, parts performance, and residual value. This knowledge informs our discussions with contractors and often becomes part of their own preferences when choosing a compressor,” he adds.

Productivity is often the underlying priority, but it can manifest in different ways, says Kuchynka.

“Brand can be a factor—some contractors have a strong preference for certain manufacturers. This could be due to past experiences with the manufacturer’s equipment or simply brand reputation. Preferences should always be determined early in the rental process and accommodated if possible,” he says.

Allmand Bros. offers the Maxi-Air Portable Air Compressor, a heavy-duty, oversized rotary screw airend designed to provide consistent, high-pressure air volumes at low revolutions per minute for enhanced fuel efficiency.

Models MA185 and MA400 provide free air delivery of 185 CFM and 400 CFM, respectively. Both models achieve a maximum working pressure of 120 psi.

The units incorporate features for ease of maintenance as well as long service intervals, notes Brian Northway, Allmand product manager.

Both models incorporate a high-capacity cold start battery to increase cold-cranking amperage for ensuring easy starting in any weather. Two 3/4-inch Chicago-style fittings provide high air output. Sound-attenuated airflow reduces operating noise to 63 decibels, about the same level as conversational speech.

The large-capacity fuel tank requires fueling once every eight hours. Should the unit run out of diesel, the electric fuel primer and air-bleed pump enables easy restarting without requiring service for priming.

All fluids in the Maxi-Air compressor are plumbed to the curbside edge of the compressor’s enclosure for easy access for maintenance. Each unit features an externally-mounted water separator filter and a radiator positioned for easy accessibility. The fiber gear coupler requires no maintenance.

A heavy-duty steel enclosure with powder-coat paint and stainless steel hardware resists corrosion. The undercarriage frame features powder-coat paint protection against tough job site conditions.

The units are designed for easy portability with long-wearing 15-inch tires as well as an adjustable coupler channel for towing the trailer level to the ground.

The MA185 runs on a 48-horsepower (hp) Tier 4 Final Yanmar engine and delivers 185 CFM of air. It features a 24-gallon tank and consumes 2.4 gallons per hour at full load capacity. Its operating weight is 2,450 pounds and it uses a 12-volt (V) electrical system. Canadian end-users have the option of the 400-CFM MA400 compressor. It runs on a Tier 3 Isuzu engine and a 24-V electrical system and weighs 5,000 pounds.

In choosing a generator, the application for which it will be used is the prime factor in making a choice, notes Melinda Doty, North American channel manager for Caterpillar.

Cat RP series generators range in size from 3.6 kilowatts (kW) up to a 12-kW portable generator while the new INV2000 inverter provides quiet power in a small compact package.

“Making sure you have the right amount of power for the job at hand is crucial,” notes Doty, adding that Caterpillar offers an online sizing calculator (which can be found here: www.cat.com/en_US/consumer/sizingtool.html).

“Next, one should look at the type of equipment that will be powered by the generator,” says Doty. “Sensitive electronics require a lower level of harmonic distortion to provide a clean energy to protect an investment.”

Caterpillar offers several options for various needs.

“Finally, one should look at the life of the product and the warranty period provided by the manufacturer,” says Doty, adding that Caterpillar offers a three-year limited warranty with the registration of the product.

The Cat RP12000E delivers 12 kW of long-lasting power for heavy-duty applications in a balanced, rugged design, notes Doty, adding that the machine is suitable for a small contracting operation.

“Built with a 670cc V-Twin OHV motor, low harmonic distortion, all-copper generator, and premium control panel, this generator delivers durable quality power for things like table saws, hammer drills, air compressors, furnaces, and smaller air-conditioning units,” says Doty.

The RP12000E offers a multitude of outlets to power more tools at one time, she adds.

“With a 13.2-gallon tank and automatic idle, the RP12000E offers extra-long run times of 11.7 hours at 50% load, a removable lifting eye, and ergonomic design,” says Doty.

“Power generation is a little bit tricky because you need to know a fair amount about what your power requirements are going to be before you can select the right genset,” says Todd Howe, manager, Doosan global generator products.

Howe notes that rental equipment is versatile and has the flexibility of different voltages for different applications, “but ultimately, the size of the generator is going to be determined by how much power the job requires.” A small generator is appropriate for a small job where a generator is needed at the job site trailer to power cord and plug tools and lighting.

Larger jobs that may feature dewatering pumps or other larger motor loads may require a more sizable generator, Howe notes.

“In a lot of cases, some of these jobs that go on a long time may have small power requirements on the front end and then the power requirements will increase as the job goes on and more equipment gets brought out and then they tail off toward the end,” says Howe. “How much power you need, when, and where is going to be a big piece of the puzzle.”

It could potentially include some permanent equipment augmented with rentals as needed, Howe points out.

Equipment with different voltage requirements is one factor that would drive getting multiple generators, says Howe.

“A job site trailer where the foreman’s office is going to be is going to run on household voltage—120-volt requirements—which would be incompatible with a 75-horsepower submersible water pump, which probably requires 40 volt three-phase,” he points out.

“If you have to have these pieces of equipment running simultaneously, you might have to have one generator set up for 120-volt applications over here and another one set up over somewhere else for 40-volt applications.”

Logistics—how often a contracting operation wants to refuel the generator—is a determining factor on a fuel tank size, says Howe.

“Sometimes generators are supplied with external tanks that fit beside them to extend the runtime,” says Howe. “What makes a generator different from any other kind of equipment on the job site is it’s usually a 24/7 application. They’re always powering something and keeping things running. They don’t necessarily shut those units off at the end of the day like they might with other types of equipment, so they run a lot and consume a lot of fuel.

“Planning to have a fuel truck come out to maintain those machines as needed and managing the service maintenance as well is very important because these gensets on a job site probably accumulate more hours than anything else. Planning those activities that do not disrupt the work that is being done is an important consideration as well.”

Doosan Portable Power offers a five-model range of small diesel rental generators spanning 25- to 150-kilovolt-amperes (kVA) power nodes and featuring Tier 4 Final-compliant engines from Doosan and Cummins.

On the small end, Doosan offers the G25, which features Tier 4 Final-compliant technology, an enclosure, and running gear. Designed with user-friendly controls, 24-hour run time, and sound attenuation, it is often used on construction sites and for emergency backups.

The generator is powered by a Doosan engine, making it easy for the company’s service network to be responsible for servicing the entire product, notes Howe.

The G25 is suitable for the job site trailer application, says Howe.

“It provides plenty of power to run all of the devices in the trailer, and the heating, lighting, and office equipment that might be inside there, and still have plenty of power left over for any cord and plug tools they may be using as part of the work process,” he adds.

The G125 generator is a mid-size machine suitable for jobs where a contracting company may be using submersible pumps for dewatering applications or larger pieces of equipment that consume more energy and require more power, says Howe.

Doosan generators have environmental containment features so fluids will not spill on the ground in the event of a failure, says Howe.

“Working in environmentally-sensitive areas, contractors can’t risk having a fuel or spill on a job site,” points out Howe. “Gensets that don’t have an environmental containment design have to be installed inside of secondary containment.”

David Scott, vice president, power and HVAC for United Rentals, notes that there are many considerations that go into choosing a generator to ensure that the equipment will provide the highest efficiency.

Of prime consideration is whether the solution will be custom or turnkey. The nature of the job site has a bearing as well.

“Is it a municipality, contractor, industrial plant, business or institution? If possible, a site visit should be made before the rental,” says Scott.

Certain basic information needed in making a choice includes generator voltage, load size in amps, the distance from the generator to load, and whether a portable unit can be placed nearby. Beyond those basics, certain questions need to be asked up front to unearth any specific needs to ensure that the most optimal equipment is specified, notes Scott.

If a generator is expected to be run for prolonged periods, an external fuel tank should be part of the plan. If the generators will be used onsite during the clearing and grading construction phase, 24-hour run time and environmental spill containment may be key features the contractor needs, he points out.

While each contractor has a different set of priorities in choosing equipment, “in general, we find that the number one priority is they want options from the rental supplier and they don’t want to compromise,” says Scott.

A broad equipment range is necessary to get the best fit, he says, adding that United Rentals Power & HVAC has more than 11,000 portable power units from 5 kW to 2000 kW with a variety of energy platforms that include gas, natural gas, diesel and solar.

Ease of operation is another priority for contractors, notes Scott.

That includes features such as three-way fuel valves, extended-run tanks, frequency controls, and integrated voltage regulators.

“We’re also seeing more requests for telematics—the idea of remote access to operating data such as fuel level is appealing to contractors as a way to manage productivity,” he says.

Allmand Bros. offers a full line of Maxi-Power Mobile Generators ranging in power output from 25 to 150 kVA.

A heavy-duty, oversized alternator with separate excitation winding provides the capacity to start large motors and handle variable loads. The automatic voltage regulator is designed to quickly adjust to provide stable and consistent voltage.

The Maxi-Power line includes a switch to change frequencies between 50 and 60 Hz. All models adjust to 120-, 240-, or 277-V in single-phase power and 208-, 240-, 415-, or 480-V in three-phase.

An electronic governor maintains engine speed independent of the load to provide consistent power. The Maxi-Power line features programmable “start and stop” capabilities for use as a standby system.

A large capacity fuel tank allows for more than 24 hours of operation before refueling. External fuel connections extend the operational time by allowing the unit to run off outside fuel. Should a Maxi-Power generator run out of diesel, the electric fuel primer and air-bleed pump help to restart the engine without the need for a service call to prime the unit. A high-capacity cold-start battery provides extra cold-cranking amps for easier starting.

Maxi-Power generators feature a dual filtration system protected in an acrylic filter housing that removes fine contaminants. Designed for full-fluid containment, the unit captures all leakage in an internal reservoir to avoid site contamination. A lockable switch voltage selector protects the engine by preventing an operator from switching voltage while the engine is running.

As with the company’s compressors, all fluids are plumbed to the curbside edge of the generator’s enclosure for easy access for maintenance. All lugs and receptacles on the machine’s curbside or rear are designed to keep end-users off the street when performing maintenance checks. Bolt-on steel fenders allow for easy in-field servicing.

A 120-V ground-fault circuit interrupter (GFCI) receptacle can be used in any voltage setting while oversized electrical lugs provide a wider range of connectability usage options.

As with the company’s air compressor units, the generators are designed for easy portability with long-wearing 15-inch tires as well as an adjustable coupler channel for towing the trailer level to the ground.

Each generator features a diesel engine. A 33.3-hp engine powers the smallest unit in the Maxi-Power line, the MP25, which provides 20 kW of prime power. The MP40 is powered by a 27-hp engine allowing 30 kW of prime power. The MP45 runs on a 59-hp engine to provide 36 kW of prime power.

Mid-range models MP65-8B1 and MP65-8C1 feature 98-hp and 76-hp engines respectively and produce 50 kW of prime power. The MP125, only available in Canada, comes equipped with a 152-hp engine and provides 100 kW of prime power. The largest Maxi-Power, the MP150, uses a 190-hp engine and produces 120 kW of prime power.

On construction sites where jobs go into the evening hours, lighting is a critical component.

Martin Ngwenya, the marketing coordinator for Hella Automotive Sales, notes that quality material is a key component in choosing lighting.

“Quality materials like the impact-resistant, hard-coated polycarbonate lens and the premium anti-corrosion aluminum housing that ensure a long lifetime and maintenance-free lighting are major factors that ensure the highest efficiency in lighting equipment,” points out Ngwenya.

“The priorities in choosing the right lighting equipment start with safety and comfort of off-highway driving operations,” says Ngwenya, adding that Hella’s ZEROGLARE optical system ensures that light from oncoming traffic does not blind oncoming drivers, thus eliminating discomfort and preventing disability glare.

The ZEROGLARE system has a sharp horizontal cut-off that directs the light onto the ground in front of the vehicle instead of into the field of vision of oncoming vehicle operators, he adds.

For mining jobs, Hella has designed LED lighting solutions that are particularly robust.

The RokLUME 380 and RokLUME 280 feature light engines of 7,500 and 4,300 measured lumens respectively, with a choice of five light distributions, including the ZEROGLARE optic.

To meet the demands of different weather conditions, RokLUME is available in two color temperatures: 5,000° Kelvin color temperature for enhanced color rendering for normal conditions, and 1,800° Kelvin color temperature for minimal backscatter when used in fog or snow.