What is a reciprocating air compressor?

Table of contents

Should you buy a reciprocating air compressor or a rotary screw air compressor? If you&#;re shopping for a new air compressor, you may be wondering about the differences between rotary and reciprocating (piston) compressors. But while both types of compressors create compressed air, there are important differences in how they work and the applications they are best suited for. 

Deciding which compressor type is right for you really depends on your air requirements: How much air (CFM) are you using? Is your air use intermittent or continuous? How clean does your air need to be? And how important are maintenance requirements and compressor efficiency in your decision? In this article, we&#;ll take a look at the advantages of rotary screw compressors vs. reciprocating compressors, the pros and cons of each compressor type, and which applications each is suited for. And we&#;ll try to answer the ultimate question: which is better, a piston or a screw compressor? 

What Is a Reciprocating Air Compressor?

A reciprocating air compressor (also known as a piston-type air compressor) uses pistons driven by a crankshaft to compress the air. Pistons were first used to compress air in the mid-s. Today&#;s reciprocating air compressors are largely the same as compressors used in the late s during the industrial revolution. 

A reciprocating air compressor works by using a piston to compress air inside a cylinder. The piston moves back and forth, drawing in air on one stroke and compressing it on the next. The basic design of a piston compressor consists of a cylinder, a piston, and a crankshaft. The cylinder is typically made of metal and is closed at one end, while the piston is a metal disc that fits snugly inside the cylinder. The crankshaft is connected to the piston and is used to drive the piston back and forth inside the cylinder.

When the piston moves downward, it creates a vacuum inside the cylinder, which draws air into the cylinder through an intake valve. As the piston moves upward, it compresses the air, which is then forced out of the cylinder through a discharge valve. This process repeats continuously as the piston moves back and forth inside the cylinder, creating an intermittent stream of compressed air.

Piston compressors can be either single-stage or two-stage. In a single-stage compressor, the air is compressed in a single stroke, while in a two-stage compressor, the air is compressed in two stages. In a two-stage compressor, the air is compressed to an intermediate pressure in the first stage, and then further compressed to a higher pressure in the second stage. This two-stage process allows for higher output and greater efficiency.

These machines are easy to maintain and excellent performers for many general-use applications. Reciprocating compressors are relatively simple in design, and many of their parts can be replaced or repaired by the user. They are best for applications that require intermittent use of small amounts of compressed air. They are often used in small shops, auto repair centers, and other settings where a high-CFM output is not required.

What Is a Rotary Screw Air Compressor? 

Rotary screw air compressors (or simply rotary air compressors) have been around since the mid-s. They use two meshing helical screws, known as rotors, to compress the air. As the interlocking spirals turn, air is forced through the chambers and compressed into a smaller space. With this process, air is continuously compressed as the rotors turn.

The basic design of a rotary screw compressor consists of two rotors, or screws, that rotate inside a cylinder. The rotors are usually made of high-strength steel and have a helical shape, with grooves cut into them to allow air to move through the compressor. As the rotors rotate, air is drawn in through an inlet valve and compressed as it moves through the compressor. The compressed air is then discharged through an outlet valve.

Because there are fewer moving parts, rotary screw air compressors are more reliable and tend to last longer compared to reciprocating compressors &#; as much as two to four times as long. While they tend to cost more up front, these advantages make a rotary compressor a good investment for many industrial users. They are preferred for applications requiring continuous operation and high airflow (CFM). One of the main advantages of rotary screw compressors is their high output capacity. They are capable of delivering continuous, high-pressure output, making them well-suited for industrial applications that require a large volume of compressed air. Another advantage of rotary screw compressors is their efficiency. They are designed to operate continuously, with minimal pulsation, which allows them to deliver a steady output of compressed air with minimal energy loss. Additionally, rotary compressors are known for their low vibration and noise levels, making them more comfortable to work around than other types of compressors.

For these reasons, rotary compressors are a popular choice for industrial applications that require high volumes of compressed air, such as manufacturing production lines, conveyor systems, process manufacturing, plastic molding, woodworking, and many more.

What Is the Difference Between a Reciprocating Air Compressor and a Rotary Screw Air Compressor? 

There are many differences between rotary and reciprocating air compressors, including operation, performance, efficiency, maintenance requirements, and CFM production. Understanding the key differences between reciprocating vs. rotary screw air compressors can help you make the best choice for your application. 

Compression Operation 

One of the main differences between reciprocating and rotary screw compressors is how they compress air. 

• Rotary screw compressors are designed for continuous operation; the helical screws in a rotary compressor produce air the entire time they are turning. That makes them a better choice for applications requiring high CFM or continuous air use. 
• Reciprocating compressors use the back-and-forth motion of a piston within a cylinder to compress air. Air is only compressed during the part of the cycle when the piston is on the upswing. For this reason, piston compressors are better for applications requiring intermittent use of compressed air.

Energy Efficiency 

When comparing the efficiency of reciprocating vs. rotary screw air compressors, reciprocating compressors have a slight edge at lower horsepower and CFM ratings, especially in intermittent-use scenarios. However, for higher CFM applications and continuous operation, rotary compressors offer a clear advantage. Overall, rotary compressors offer higher CFM per horsepower than reciprocating compressors. There are a few reasons for this. 

• Rotary compressors use fewer moving parts than piston compressors. 
• A rotary screw compressor produces air the entire time it is in operation, while a reciprocating compressor only produces air during half of its cycle. 
• Reciprocating compressors lose more energy to friction and motion of their moving parts compared to rotary compressors.
• Reciprocating compressors have more internal leakage due to the design and motion of the pistons, cylinder and ring wear, which further reduces their efficiency. 

Maintenance Requirements 

There are two considerations when it comes to air compressor maintenance: How much (and how often) is maintenance needed? And how much can you do yourself? 

• Piston compressors have more moving parts and require more frequent maintenance to maintain optimal performance, including oil changes and filter replacements. They also require regular replacement of valves and piston rings that wear out due to the constant friction of the reciprocating motion. Compressor parts and maintenance for piston compressors can get expensive over time. However, their simpler design means that it is easier to perform much of this maintenance in-house. 
• Rotary screw air compressors have fewer moving parts to wear out and require less overall maintenance than piston compressors. Regular maintenance for rotary compressors is generally limited to checking and changing the oil, oil filter, and air/oil separator. But because they are more complex machines, screw compressors usually require a skilled maintenance team for preventive maintenance, repair, and upkeep. That may mean outsourcing more maintenance to the experts. 

Initial vs. Lifetime Costs

Cost is always an important consideration when choosing between rotary and reciprocating compressors. It is important to consider both the initial investment and the total cost of ownership over the lifetime of the compressor. In general, a reciprocating compressor is a better value at the low end of the industry (10 HP or less), but rotary compressors provide better overall value at higher HP ranges. The more CFM you require for your applications, the better the cost savings of a rotary compressor. 

• A reciprocating compressor costs less than a rotary compressor of equivalent CFM, making them a more accessible capital investment for smaller shops that do not require the continuous air use and efficiency of a rotary compressor. However, the cost of replacement parts and maintenance adds up over time. Energy costs per CFM will be higher at higher CFMs, which will drive up energy costs for producing air. In addition, a piston compressor usually has a much shorter lifespan than a rotary compressor, which means you&#;ll have to replace it much sooner. 
• Rotary screw compressors are generally a bigger investment up front. But over their lifespan, the cost savings can be dramatic, especially at higher horsepower and CFM ratings. Cost savings come from lower energy consumption, lower overall maintenance requirements, and a longer expected lifespan. In fact, with proper maintenance, the average rotary compressor can last twice as long as a comparable piston compressor: 100,000 hours or more vs. 50,000 hours or less depending on the quality of the compressor. 

Reliability 

For applications requiring a highly reliable source of compressed air, rotary screw compressors once again come out on top. 

• Rotary compressors tend to be more durable than piston compressors, as they are designed to operate continuously and can handle high volumes of compressed air. Rotary compressors are also less likely to suffer from mechanical fatigue or stress, as their design allows for smoother operation and fewer vibrations. This all contributed to higher reliability and fewer unexpected breakdowns over time. A well-maintained rotary screw compressor can deliver clean, consistent air for many years.
• Reciprocating compressors are subject to greater mechanical strain, which results in higher maintenance requirements and a greater chance of unplanned downtime. Downtime can be minimized with timely preventive maintenance and prompt replacement of worn parts. However, piston compressors may have an advantage in dirty environments, as they are less sensitive to problems caused by airborne particulates and moisture.  

Lifespan

Rotary screw compressors usually last much longer than reciprocating or piston compressors, up to twice as long on average. 

• An oil-flooded rotary screw compressor can last for up to 100,000 hours with proper care and maintenance, or up to 20 years. With proper preventive maintenance, including regular oil changes, filter replacement, and inspections, they can last even longer. Oil-free screw compressors don&#;t last quite as long; they will typically run for 70,000 hours (10-15 years) before needing a rebuild or replacement. 
• A reciprocating compressor usually lasts for about 50,000 hours, or less, depending on use conditions, maintenance and quality. 

Integrated Air Tanks and Air Storage Requirements 

Both rotary screw and reciprocating compressors may utilize air receiver tanks.

• An air tank is generally required for a reciprocating compressor. Most piston-style compressors come with integrated air tanks. Air storage is required due to the intermittent way that piston compressors produce air. The tank ensures that there will be enough air ready when it is needed. 
• Some rotary compressors come with an integrated air tank, but many do not, especially the larger compressors used for heavy industrial applications. Because they produce air continuously, it is possible to use these compressors without an air tank. However, a combination of wet and dry air storage is usually recommended to improve system efficiency and provide power for high-demand events. A tankless rotary compressor allows system designers to customize the storage system for the application and air demand. 

Operating Environment

The operating environment can have a big impact on air compressor performance, reliability and maintenance requirements. Particulates in the air &#; such as pollen, dust, particulate from combustion engines, and other airborne contaminants &#; can gum up the works inside the air end, contaminate lubricants, and clog inline filters. In general, reciprocating compressors are less sensitive to particulates in the air supply. 

• Rotary compressors operate best in a relatively clean indoor environment. If intake air is not clean, filtration can help to remove most contaminants before air enters the air end. 
• If the compressor will be placed outdoors or in a very dirty indoor environment (e.g., a mechanic shop), a reciprocating compressor may be a better choice. 

Noise

Compressor noise can be an important consideration, especially if equipment will be operated in environments where people will also be working. Piston and rotary compressors differ in their noise level, with rotary compressors generally being quieter than piston compressors. Here are some factors that contribute to this difference:

• Reciprocating compressors have a more complex design than rotary compressors, with more moving parts that can cause noise and vibration. They operate with a more pulsating motion, which can create more noise and vibration than the continuous motion of rotary compressors. Piston compressors are typically smaller than rotary compressors, and the smaller the compressor, the more noise it tends to make. They also tend to not have as much sound insulation, especially in smaller models.
• Rotary compressors, on the other hand, have a simpler design and fewer moving parts, which can reduce noise and vibration. They typically operate with a more steady flow of compressed air, which can reduce noise and vibration, and are often designed with built-in sound insulation to reduce noise. 

Size and Space Requirements for Installation

Both types of compressors require ample free space and ventilation around the machine to prevent overheating. When looking at space requirements for compressor installation, be sure to take into account the need for ventilation space as well as room for the compressor and all its components. 

• In general, a rotary screw compressor will take up less space than a reciprocating compressor of equivalent CFM output. That&#;s because you can get more CFM with a lower HP motor. In addition, the air end itself, with its spiraling rotors, is a more space-efficient design than the moving pistons required for a reciprocating compressor. Finally, screw compressors are available without an integrated air tank, providing further flexibility in system design and compressor placement. 
• A reciprocating compressor generally comes with an integrated air tank, so it is important to look at the total size of the unit, including the compressor and tank, when evaluating space requirements. 

Duty Cycle

One of the biggest differences between piston vs. screw compressors is in the duty cycle. The air compressor duty cycle is the amount of time it spends producing air vs. the amount of time it spends resting (also known as load/unload time or run/rest time). 

• Rotary screw air compressors are designed for 100% duty cycle. In other words, they can produce air 100% of the time. These compressors are also known as continuous duty cycle. If less air is needed, the compressor will turn off (unload) for short periods of time; when pressure drops to a preset level, they turn back on. If you need a continuous-run compressor, rotary screw is the way to go. 
• Reciprocating compressors are designed for intermittent duty cycle. These compressors need to cycle down and cool off intermittently. The compressor will be rated for a specific duty cycle (e.g., 25% duty cycle, 50% duty cycle, 75% duty cycle, or 100% duty cycle). The lower the duty cycle rating, the more time the compressor must spend resting vs. making air. It is important to avoid over-cycling the compressor, or forcing it to spend a higher percentage of time making air than it is rated for. This will cause overheating and lower compressor life. Most piston compressors are rated for 20-30% duty cycle. 

Pressure Bands 

Rotary screw and reciprocating compressors differ in their ability to maintain even pressure (PSI) in a plant. The pressure band is the difference between the cut-in pressure (the point at which the compressor will start making air) and the cut-out pressure (the point at which the compressor will stop making air). In other words, how much pressure is allowed to fluctuate. 

• If your applications have very tight pressure tolerances, a rotary screw compressor will generally operate within a smaller pressure band. A variable speed drive (VSD) rotary screw compressor will offer the tightest pressure bands, operating within a +/- 1.5 PSIG tolerance. This allows plants to lower overall plant pressure without dropping below minimum PSI requirements. A fixed-speed rotary compressor will still generally have a smaller pressure band than a piston compressor because they are able to make air continuously to maintain PSI. 
• Because piston compressors produce air intermittently and generally are rated for less than 100% duty cycle, their pressure bands tend to be much higher, as much as +/- 10-30 PSIG. Having an adequately sized storage tank is essential to even out PSI and maintain adequate delivery pressures. 

Maximum Delivery Pressure

When choosing a compressor, it is important to ensure that its maximum delivery pressure (PSI) meets your needs. Most industrial applications require pressure of 100 PSI. Both rotary screw and reciprocating compressors can easily meet this requirement. For high-pressure applications requiring PSI of over 120 PSI, a multi-stage compressor may be needed. 

• Rotary screw single-stage compressors can deliver pressure of up to 150 PSI. A two-stage screw compressor can reach pressures above 175 PSI. However, their primary advantage is that they can deliver more CFM with greater efficiency. Screw compressors are not generally used for high-pressure applications. 
• Piston compressors can compress air to 120 PSI during a single stage of compression and 175 PSI during two-stage compression. Higher pressures may be achieved with additional stages of compression. High-pressure air compressors are almost always piston compressors with 3- or 4-stage compression. They are capable of compressing air to very high pressures, up to 6,000 PSI or more, and are generally used for specialty applications. 

Cleanliness of Delivered Air 

With proper filtration and air treatment, both piston and screw compressors can deliver clean, high-quality air. However, rotary compressors do have an advantage here. 

• Rotary compressors deliver very clean air with low oil carryover and particulate contamination. Rotary screw compressors have a more enclosed design than piston compressors, which helps to keep the compressed air clean and free of contaminants. They are also less prone to oil leakage and contamination due to their design. Many rotary screw compressors also have internal filtration to remove contaminants in the oil. 
• In a piston compressor, the cylinder and piston can be exposed to the surrounding environment, which can allow dust, dirt, and other contaminants to enter the compressed air. They are also more likely to experience oil leakage and contamination in the air supply. 
• If extra-clean air is needed, both reciprocating and rotary screw compressors come in oil-free models (though rotary screw are more common). However, an oil-flooded rotary screw compressor with good filtration will work for all but the most exacting applications. Oil-free compressors are more expensive to buy and maintain and have a shorter lifespan compared to oil-flooded compressors. Read more: Do You Need an Oil-Free Compressor? 

Application Suitability 

Reciprocating and rotary screw compressors are both suitable for a variety of applications, but there are some differences in the types of applications for which each type of compressor is best suited. 

• Reciprocating compressors are well-suited for smaller-scale applications that require lower CFM and intermittent air use. They are often used in workshops, small manufacturing operations, and in the automotive industry for tasks such as powering air tools or inflating tires. Reciprocating compressors are also well-suited for applications that require occasional operation, as they can be turned on and off as needed.
• Rotary screw compressors are better suited for large-scale industrial applications that require high output and continuous use. They are often used in manufacturing plants, food and beverage processing, and other industries that require a continuous supply of compressed air. However, they may not be as well-suited for applications that require intermittent operation, as they are designed for continuous operation.

Average CFM per Horsepower by Compressor Type

Reciprocating

CFM @ 175 PSI

Rotary Screw

CFM @ 150 PSI

CFM @ 125 PSI

5HP

18

5HP

16

18

7.5HP

24

7.5HP

26

38

10HP

35

10HP

38

40

15HP

50

15HP

For more information, please visit high pressure reciprocating compressors.

54

60

20HP

80

20HP

78

85

25HP

95

25HP

102

108

30HP

125

130

40HP

155

160

50HP

185

200

60HP

210

235

Pros and Cons of Reciprocating vs. Rotary Screw Air Compressors

Which is better: a reciprocating or a rotary compressor? Choosing between a reciprocating and a rotary screw air compressor depends on how you use compressed air, how much compressed air you need, and the environment that the compressor will be operating in. This handy chart provides an overview of the pros and cons of reciprocating vs. rotary air compressors.  

Reciprocating Air Compressor

Rotary Air Compressor

Pros

&#; Low initial capital investment (20-50% less than rotary) 

&#; Simple maintenance 

&#; Can be run in sheltered outdoor or dirty indoor environments

&#; Better energy efficiency for low CFM, intermittent applications

&#; Capable of higher pressures with multi-stage compression 

Pros

&#; 100% duty cycle 

&#; Higher CFM per HP

&#; Cleaner air (less oil carryover, typically 3-8 ppm) 

&#; High reliability 

&#; Longer life (lower total cost of ownership over time)

&#; Cooler internal operating temperature (140 - 160°F)

&#; Quiet operation 

&#; Air receiver tank not required

&#; Better energy efficiency for high CFM, continuous applications

Cons

&#; Interrupted flow rates

&#; Requires more frequent maintenance

&#; Noisy (up to 100 dB)

&#; Hot (internal operating temperature 150-200°F)

&#; High oil carryover (10-50 ppm)

&#; Lower life expectancy 

&#; Lower reliability and uptime 

Cons

&#; High initial capital investment

&#; Requires skilled maintenance

&#; Requires clean operating environment 

Best For

&#;&#; Intermittent use (20-30% duty cycle)

&#;&#; Lower CFM

&#;&#; Smaller shops and manual applications (e.g., manual power tools, blow-off, etc.)

Best For

&#;&#; Continuous use (100% duty cycle)

&#;&#; Higher CFM

&#;&#; High-volume and robotic manufacturing and conveyor systems

&#;&#; Applications requiring very clean air (e.g., paint shops, food processing)

 

Choosing the Right Air Compressor for Your Application 

Which type of air compressor is right for you? It really depends on your application. Reciprocating compressors are more versatile and easier to maintain, while rotary screw compressors offer higher output and are better suited for large-scale industrial applications. The advantages of rotary screw air compressors are quite apparent when it comes to large-scale industrial applications requiring continuous airflow or high CFMs. On the other hand, if your compressed air needs are more intermittent, a piston-style compressor may just fit the bill. 

When to Use a Reciprocating Air Compressor

Reciprocating or piston-type air compressors are best for applications when you are using short bursts of air intermittently. A reciprocating compressor is a great choice for homeowners and DIYers, small machine shops, construction work and other small businesses. A reciprocating air compressor can be used to run manual air-powered tools and for blow-off and cleaning, tire inflation (and other inflatables), airbrushing and sandblasting. 

One advantage of a reciprocating air compressor is that it is not damaged by being run intermittently or below its maximum capacity. That means you can purchase a larger machine to &#;grow into&#; if you know your shop will require more air in the future. In fact, it is recommended that the reciprocating air compressors be sized at 50% higher than the required CFM to allow the compressor to cycle properly and avoid excessive heat generation and wear and tear on the motor.

When to Use a Rotary Screw Air Compressor

Rotary air compressors are best for applications that require continuous air. These are the workhorses of the industry, used to power robotic manufacturing equipment and conveyor systems. They are designed to operate nonstop and produce a strong and consistent flow of air. Because the air produced by rotary air compressors is much cleaner than air produced by reciprocating compressors, they are the best choice for paint lines, food processing and packaging, and other applications where clean, dry air is essential. 

Fixed-speed rotary screw compressors are not designed for intermittent use efficiently and may experience performance issues if they are not used close to their full capacity. If your compressed air demand varies, but you want the advantages of a rotary screw machine, you may want to consider a variable speed drive (VSD) compressor. While a fixed-speed compressor is always operating at the same RPM, a VSD motor can ramp up or down depending on demand.

Aire Tip: If your compressed air demand is variable, a VSD rotary screw compressor can reduce energy costs for your compressed air system by up to 70%.  

Conclusion: Choosing the Best Industrial Air Compressor 

What&#;s the best type of compressor? As you can see, it depends on your application and use case. There are many factors to consider when choosing between a rotary screw and a reciprocating air compressor. 

If you need a little help, the experts at Fluid-Aire Dynamics can help you evaluate your needs and decide on the best compressor type for you. We carry a large stock of both reciprocating and rotary screw compressors in sizes from 5-10 HP to 400 HP and up, including VSD compressors. We are here to support you with compressor selection and compressed air system design, whether you need a small piston compressor for occasional use or a large rotary screw compressor for heavy-duty industrial applications. Contact our Aire Experts today! 

 

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