Air Compressor Buying Guide
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Air compressors have evolved over the years to play a more significant and integral role in our homes and workplaces. An air compressor works by drawing in surrounding air, then pushing it out through mechanical components under pressure, into a usable force that can be used for powering pneumatic tools.
You can set the desired air pressure level (PSI) for whichever tasks you need. One of the critical factors to choosing the right air compressor is the amount of air volume it can generate, measured in cubic feet per minute (CFM).
Whichever task you need to perform with an air compressor, we’ll help you choose the right air compressor for your needs. This guide will show you can pick the right tool for the right job.
Air Compressor Types
Despite the different types of air compressors available in the market today, all compressor types have a single common function – turning compressed air into pressured energy.
A reciprocating (piston) compressor builds up air pressure by decreasing the volume of air. When a reciprocating compressor operates, it takes in a high volume of air and contains it inside a sealed tank.
Using a piston and an internal motor, the compressor spins into motion to build up the pressure in the tank. The piston moves in an upward and downward motion inside a cylinder, squeezing vapor refrigerant the condenser.
Reciprocating compressors come in both water-cooled or air-cooled variants, and subsequently in non-lubricated and lubricated configurations.
These different variations enable manufacturers to produce various capacity and pressure options. On top of that, there are also single-stage and two-stage and single-stage reciprocating compressors.
Single stage compressors are single-action compressors that compress air only from one side of its piston. Single-stage compressors can produce pressures from 70 to 100 PSI.
Two-stage compressors use both sides of the piston. Because of their double-action compression, they can produce anywhere from 100 to 250 PSI.
- A diverse range of applications in both industrial and home
- Relatively cheap installation cost
- Low cost of maintenance
- Ability to produce a high amount of air flow
- Easy to service and repair
- The compressor itself is expensive
- Requires regular inspection to increase its lifespan and internal pressures in check
- Parts can wear & tear quickly
- Can be unsightly due to its size
Rotary Screw Compressor
If you’ve ever paid a visit to any huge manufacturing building, chances are their production process involves a rotary screw compressor. As workhorses to the manufacturing industry, a typical industrial rotary screw compressor has a 100 percent duty cycle, which means they can run non-stop for 24 hours a day, seven days a week.
Rotary screw compressors last longer and operate better when they are run continuously unlike reciprocating compressors that use pistons and needs to be stopped from time to time.
Rotary screw compressors work by spinning two rotors (or screws) compress the air. The operating pieces are not exposed to any high temperatures since the cooling occurs internally. This makes the rotary compressor is a heavy duty machine that doesn’t stop working.
For rotary screw compressor to operate effectively, it uses a special filter, making operation and maintenance a breeze. There is also a sliding valve inside that adjusts the level of displacement. When the capacity of the compressor drops, the valve slides open, letting some compressed air flow back to the suction.
One of the key advantages of a rotary screw compressor is its ability to produce pulse-free, consistently smooth air output at a high volume.
Rotary screw compressors come in either oil-flooded or oil-free variants. An oil-free compressor uses specially built air valves to compress air. The result is air that is clean and oil-free.
Oil-flooded compressor creates compressed air using a thin layer of oil in between the rotors. The oil also serves as a sealant and coolant inside the compression chamber.
- Cheaper initial installation and purchase cost than a reciprocating compressor
- Potential to last around up to 5 times longer than other types of compressor
- Usually consumes a low level of energy
- The cooling cycles can last for a long time
- When compared against piston compressors, rotary screw compressors are expensive
- Some types of screw compressors require more maintenance than piston compressors
- Rotary screw compressors are highly vulnerable to poor maintenance and non-standard parts.
A rotary-scroll compressor can compress larger volumes of gaseous refrigerant to a higher pressure and temperature using a pair of scrolls – one fixed and one orbital. This type of compressor is usually found in commercial air conditioning and refrigeration systems.
Each operation cycle consists of three actions: suction, compression, and discharge. Some rotary scroll compressor can regulate their cooling capacity by increasing the gap between scrolls intermittently, keeping the contents cool (or warm).
The lesser the load, the more time the scrolls stays apart, preventing refrigerant from flowing into the compression process.
- More reliable than other compressor types thanks to fewer components and simple structure
- Higher efficiency
- Subjected to lesser vibration and surging
- Smaller capacity
- Lower efficiency
Centrifugal compressors rely on energy transfers from its rotating impeller to the air. An impeller is a disk with radial blades, which spins quickly inside the cylinder. The spinning impeller drives the gases, causing them to speed up.
At the same time, a diffuser builds pressure energy that flows into a condenser. The faster the impeller can spin, the higher the compressor’s pumping efficiency. Centrifugal compressors are designed to run at high speeds.
Because centrifugal compressors don’t contain minimal moving parts, they are easy to maintain. Like reciprocating compressors, centrifugal compressors come in single-staged or multi-staged. The more stages a compressor has, the higher its efficiency.
Single-staged centrifugal compressors only have one impeller. It delivers high efficiency and oil-free air. Multi-staged compressors can have up to 10 impellers. They can also take various arrangements – double-flow, compound or straight-through.
- Lighter weight
- Can supply a continuous stream of compressed air
- Produces oil-free air
- Minimal rubbing parts to replace.
- The high airflow output rate
- Require very little maintenance, highly reliable
- Struggles to deliver extremely high compression
- Prone to chokes, stalls, and surges
- Requires vibration dampening mounting due to internal high-speed movement
Gas-Powered Air Compressor
Gas powered air compressors run on natural gases. These are excellent options for outdoor use and in remote areas where they send out consistent air pressure and high-pressure compression. This compressor can be noisy, and also produce noxious gases. For these reasons, it needs to be located in places where there is excellent ventilation.
Without the need to plug into an electrical power source, you won’t need to be restricted by any electrical requirements. A typical natural gas air compressor is much more durable than electric compressors and can be more efficient.
Electric Air Compressor
Electric air compressors have a unique advantage over gas powered compressors because they can operate in almost any scenario, as long as there is electricity. With a steady stream of electricity, this air compressor can work non-stop, without the need to stop and refuel.
More importantly, electric compressors don’t exhaust any harmful gases, odors or noise, making them safe and less distracting. With electric air compressors, you can quickly relocate them as they are lighter and more compact than gas air compressors.
Single-stage vs. Two-stage Compressor
In single-stage compressors, the air is compressed once between the inlet valve and nozzle; whereas in a two-stage compressor, the air is compressed twice. Hence the pressure is doubled.
Single stage compressors are found in reciprocating piston compressors. First, the air gets sucked into a cylinder, which is then compressed inside and stored in a tank. This compressed air can then serve as energy for different types of work tools that are compatible with the compressor.
In a two-stage compressor, the process is similar, but instead of compressing the air into the storage tank, it is delivered to a secondary piston to be pressurized a second time. The result is a much higher pressurized air that can be used to run higher-powered equipment.
Oil-lubricated vs. Oil-free Compressor
Air compressors suck in air in using a piston. For a compressor to gather maximum efficiency, the piston chamber needs to be adequately lubricated. Oil lubricated compressors use oil to lubricate the piston chamber. On the other hand, oil-free compressors do not require oil lubrication. The piston cylinder is usually pre-lubricated permanently (such as using Teflon) With Teflon coating protecting the pump, it can last longer without the need for constant oiling.
Air Compressor Tank Style
There is an assortment of tank styles to choose from, depending on your requirements.
Hot dog compressors are the preferred choice for most hobbyists. These types of compressors can easily power small hand pneumatic tools, such as airbrushes. Their main drawback is they are bulky and take up a large footprint. While hotdog compressors are typically low-maintenance, they tend to generate a significant amount of noise during operation.
Pancake compressors usually small in size and are very lightweight. The tank volume ranges from 1 to 6 gallons on average, and the tank itself is designed for portability. Pancake compressors also require very little maintenance. They are excellent options for small and medium tasks such as inflating tires. However, for larger projects, you may find their power severely lacking.
Also called twin-stack compressors, these are mostly standard hot dog compressors stacked on top of each other. Twin-tank configuration gives you a more substantial air capacity, which makes them ideal for powering nail guns and doing trim work. For their capacity, they are sturdy and portable, but some designs can weigh as much as 70lbs.
Wheelbarrow air compressors place their tanks along the length of the compressor. They look like a wheelbarrow and offer the same mobility. They usually come with powerful motors affixed on top and are perfect for heavy-duty projects. The tanks are durable and can be dragged along rough terrains without getting damaged, but they can be very heavy for lifting (sometimes up to 300lbs).
Stationary Horizontal and Vertical
These are huge and immobile compressors that are designed to create high-pressure air and power heavy duty tools. The critical difference between a horizontal and a vertical compressor is the amount of floor space they both take up. If floor space is an issue (such as in a home garage or small factory), then a vertical compressor will be the ideal choice. On the other hand, horizontal compressors can be fitted under work desks and benches.
Truck mounted compressors are some of the most powerful mobile compressors you can buy. They are enormous and heavy, weighing several hundreds of pounds, but they can have the power to perform any task.
Choosing The Right Air Compressor
Although your options for air compressors can be overwhelming, you can narrow down your choices by asking these key questions.
What is the application?
Because air compressors can perform a diverse range of tasks, you need to determine what type of compressor you need for your usage.
- Portable compressors, like pancake and hotdog compressors, are ideal for one-person operations and small hand tools.
- Stationary, single-stage air compressors are good options for carpentry workshops, automotive garages or facility maintenance businesses.
- Multi-staged air compressors are great larger scale operations, such as automotive workshops that can service 2 or more cars.
- Rotary screw air compressors are ideally suited for applications that need a continuous flow of air, where compressors are required to operate at 100 percent all the time.
What pneumatic tools will you be using?
Some pneumatic tools require a high volume of air to operate. This can be measured using a metric unit called standard cubic feet per minute (SCFM). To choose the right compressor, take the tool that requires the highest amount of SCFM and multiply the number by 1.5. If you are using multiple pneumatic tools, add their scfm together and multiply that number by 1.5. With that number in mind, choose the compressor that can deliver a cubic feet per minute output that is equal or higher than the number in your formula.
What type of power is available?
Different type of compressors has different power requirements to operate at full capacity. For example, portable compressors usually run on 115-volt, 15-amp circuits.
While stationary, single-stage compressors can require up to 230-volt, single-phase power to run. If you are unable to find an electrical power source, you have to go with a gas-powered air compressor instead.
Other Features to Consider
- Max PSI
When you choose a compressor, you need to know how much pressure you need for your usage. While PSI (pounds per square inch) is not a critical factor, but it shouldn’t be ignored.
For example, small air compressors with a high max PSI can hold more air than large tanks with lower max PSI rates, because of a higher percentage of air compression.
Also, users who have limited storage space may want to opt for air compressors that have a smaller tank to address space constraint issues.
Most importantly, you should check your pneumatic tools’ PSI ratings to make sure that your compressor can operate under the right amount of pressure. For example, nail guns need a minimum of 120 PSI to work correctly.
A compressor’s horsepower rating is a key metric to determine how well it can operate. A 5 HP air compressor will not be able to perform at the same level as a 100 HP air compressor.
However, take note that horsepower alone doesn’t tell the whole story of the capabilities of a compressor. You will need to study other factors such as capacity and pressure.
- SCFM ratings
Your pneumatic tools should have SCFM ratings that indicated the required amount of airflow for optimal performance. Don’t forget to use the formula of multiplying the highest rated SCFM tool by 1.5. A lot of light-duty home compressors are only capable enough to operate one device at a time, but bigger scale professional-grade compressors can handle multiple pneumatic tools.
- Noise Level
When operated for prolong periods, air compressors can become a source of noise pollution. Not only are they a distraction, without proper ear protection such as earplugs, but your ears can also potentially be damaged permanently.
Fortunately, there are quiet air compressors in the market engineered to produce less noise. If you are concerned about the level of noise, choosing a quiet air compressor provide you with the versatility and peace that you need.
While choosing the right air compressor for your application may be intimidating at first, reading this guide should equip you with the proper knowledge and info to make an informed buying decision.