Single stage vs. 2-stage air compressor - advantages at ...

Clive603 said:

Just recalled where the manual for my retired Atlas KE Vee twin compressor was hiding. These units came in 3 sizes and 15 versions. A quick look shows the single stage KE series are rated at 100 psi and the otherwise identical two stage KT versions are rated at 200 psi. Interestingly the output is given as piston displacement at specified run speed not directly as air delivery. I guess this avoids many potential specification mis-read problems as its then down to the user to figure out exactly how much air he (or she) gets at what temperature. My 3 hp KE2 was rated at 16.2 cfm piston displacement running at rpm. The lower pressure KE23 version running at rpm delivers 45 psi from 19.5 cfm piston displacement.

The KT2 version has two piston displacement ratings 7.32 and 9.75 cfm covering 2 HP 900 rpm and 3 hp rpm drive. The manual also lists a higher pressure 18 suffix version rated at 255 psi and 8.13 cfm piston displacement running at rpm.

Its interesting to see that specified running speed varies from 720 to rpm for various versions despite similar design. My mate Andy also got a KE2 from the same scrappy and ran his at 130 psi but the last 10 psi were very slow. I haver seen single stage units installed to deliver 150 psi. Hot air!

Clive

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Heating the air in compression can actually help. If you start with room temperature air and compress it, the heating makes it expand so it has a larger volume and lowered viscosity, making it push out the exhaust valve faster. If the tank is large enough that the air in it is reasonably cool, that air temperature defines the back pressure, not the air going through the exhaust port. If the heat conduction between the intake and exhaust ports is high enough to significantly heat the incoming air, then the compression stroke starts with a smaller charge and resultant loss in output. Cool in, hot out improves the throughput.

The manufacturer only listing displacement (swept volume) is just dodging the issue. A good spec sheet gives the actual output at various pressures. These compressors never deliver the full swept volume. Running at slow speeds and against low back pressure, they may come close, but all drop off when they have to work hard. Configured as a two stage where the low pressure cylinder was only working against about 15 PSI in the manifold between the cylinders, at 62 CFM swept volume and 100 PSI it actually delivered 56 CFM. That is about the best you could expect. I sized the orifice in the bead gun to match and sent the air through the cooler and to it, only feeding the 200 gal. tank when not blasting. With the large storage, other people in the shop never noticed.

Another factor usually neglected is the force needed to open an atmospheric intake valve. Running my Gardner Denver ACR as a vacuum pump, it would rapidly go up to 25 in hg gauge and stop. The approximately 4-5 in difference between that and atmospheric pressure was the differential needed to actuate the valve. That difference is also subtracted from the fill pressure when it is used as a compressor, although that is mitigated a bit because once the valve snaps open, it will tend to stay.

The viscosity of the air can have a surprising effect. I once repaired some huge heaters for an aluminum annealing oven big enough to handle truck loads. The operator commented that even though he had the blower motors rewound for the maximum performance possible, he had to start with the blowers off and heat the air until it got thin enough to avoid overloading them.

All these factors get in the equation, which isn't simple.

Bill

Heating the air in compression can actually help. If you start with room temperature air and compress it, the heating makes it expand so it has a larger volume and lowered viscosity, making it push out the exhaust valve faster. If the tank is large enough that the air in it is reasonably cool, that air temperature defines the back pressure, not the air going through the exhaust port. If the heat conduction between the intake and exhaust ports is high enough to significantly heat the incoming air, then the compression stroke starts with a smaller charge and resultant loss in output. Cool in, hot out improves the throughput.The manufacturer only listing displacement (swept volume) is just dodging the issue. A good spec sheet gives the actual output at various pressures. These compressors never deliver the full swept volume. Running at slow speeds and against low back pressure, they may come close, but all drop off when they have to work hard. Configured as a two stage where the low pressure cylinder was only working against about 15 PSI in the manifold between the cylinders, at 62 CFM swept volume and 100 PSI it actually delivered 56 CFM. That is about the best you could expect. I sized the orifice in the bead gun to match and sent the air through the cooler and to it, only feeding the 200 gal. tank when not blasting. With the large storage, other people in the shop never noticed.Another factor usually neglected is the force needed to open an atmospheric intake valve. Running my Gardner Denver ACR as a vacuum pump, it would rapidly go up to 25 in hg gauge and stop. The approximately 4-5 in difference between that and atmospheric pressure was the differential needed to actuate the valve. That difference is also subtracted from the fill pressure when it is used as a compressor, although that is mitigated a bit because once the valve snaps open, it will tend to stay.The viscosity of the air can have a surprising effect. I once repaired some huge heaters for an aluminum annealing oven big enough to handle truck loads. The operator commented that even though he had the blower motors rewound for the maximum performance possible, he had to start with the blowers off and heat the air until it got thin enough to avoid overloading them.All these factors get in the equation, which isn't simple.Bill

Table of contents

The main difference between a single-stage and a two-stage air compressor is the number of times the machine compresses air in its pressure side before sending the air to its tank. Each type of compressor also differs in the shape of its compression cylinder. As a result, two-stage compressors provide air with higher pressure than one-stage compressors.

What Is a Single-Stage Air Compressor?

A single-stage air compressor compresses air in its pressure side only once before delivering it to its tank. It draws air into a cylinder and compresses it at 90-120 pounds per square inch (PSI) before moving it to the attached storage tank. The storage tank holds a large volume of air and maintains the air&#;s pressure until it feeds air-powered tools.

In a single-stage air compressor, the cylinder holds two pistons of the same size. Due to their equal size, the cylinder has the same physical dimensions on both sides. The pistons draw air through the compressor&#;s filter element, past its intake valves and into the cylinder.

The pistons push upward as the crankshaft rotates, and the air compresses as the machine forces it through its exhaust valves. It then moves through the compressor&#;s discharge tube and the check valve until it reaches the storage tank.

What Is a Two-Stage Air Compressor?

A two-stage air compressor is also known as a dual-stage compressor, and it compresses air in its pressure side twice before moving it to its tank. After drawing air in and compressing it, a two-stage compressor then compresses the air again in a second cylinder where it is compressed to a higher pressure at approximately 175 PSI before it cools and moves to the storage tank. This delivers air at a higher PSI so the storage tank can feed more pressure to air-powered tools, which allows them to operate with a high running pressure.

While a single-stage air compressor&#;s pistons are the same size, a two-stage compressor contains one large, low-pressure piston and one small, high-pressure piston. These pistons both work together to compress the air twice. Because of the different piston sizes, a two-stage compressor&#;s cylinder also has a different shape with a smaller side and a larger side.

In a two-stage compressor, the larger, low-pressure piston draws air in and through the compressor&#;s filter before it passes the intake valve and enters the cylinder. The low-pressure piston pushes upward and the crankshaft rotates, compressing the air as the compressor forces it through the low-pressure exhaust valve. The air moves through an intercooler and reaches the pump&#;s high-pressure side where the cylinder compresses it a second time.

After the second compression, the air moves through the discharge tube and the check valve before it reaches the tank.

Single-Stage vs. Two-Stage Air Compressor

Single-stage and two-stage air compressors are different in various aspects. Since two-stage compressors provide higher-pressure air than single-stage compressors, each machine is suitable for different purposes, and each has different benefits and downsides. Single-stage and two-stage air compressors differ in the following ways:

Applications

Since a two-stage air compressor allows air-powered tools to operate with a higher running pressure, it works best for tools with a high PSI or cubic feet per minute (CFM) rating such as paint guns and blast cabinets. Large-scale operations that require significant air amounts over long periods of time will need two-stage air compressors to meet their needs while smaller facilities can typically operate with single-stage air compressors.

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Contact us to discuss your requirements of Horizontal Two-Stage Air Compressor. Our experienced sales team can help you identify the options that best suit your needs.

Reliability

Two-stage compressors typically perform better than their single-stage counterparts, and they tend to be quieter while single-stage compressors tend to operate with a higher noise volume. A two-stage air compressor runs cooler and more efficiently than a single-stage one. While a single-stage air compressor can reliably power smaller-scale machinery, a two-stage type is necessary for larger machinery that requires more air pressure for operation.

Cost

Single-stage air compressors typically weigh less and cost less because they contain fewer parts. Additionally, single-stage electric compressors use fewer amps than two-stage air compressors. A single-stage air compressor is an excellent choice for smaller businesses and individual tradesmen because it is more cost-effective for small-scale projects and jobs.

Before you purchase a single-stage or two-stage air compressor, remember that energy-efficient compressors can help you save money on energy costs.

Frequency of Use

Air compressors also differ in the length of time they can power machinery effectively. Single-stage air compressors are best for intermittent use while two-stage compressors are ideal for ongoing operation. Two-stage compressors can handle non-stop use, so they are best for large-scale industrial applications that require ongoing power.

Maintenance

Two-stage air compressors cost more because they contain more parts. However, two-stage compressor parts are smaller and require less frequent maintenance. Even though a two-stage type may cost more, it can save you money on maintenance costs over time.

Temperature

Air temperature also differs between single-stage and two-stage air compressors. Since two-stage compressors send air through an intercooler, the air has a chance to cool before it enters the storage chamber. In a single-stage compressor, the air can overheat quickly if it is overused.

Is a Single-Stage or Two-Stage Air Compressor Better?

Single-stage and two-stage compressors offer quality air compression, but the type that will work best for your operations depends on certain factors. One factor is your budget. Since two-stage air compressors cost more than their single-stage counterparts, you will need to consider your budget and how much you can afford to spend on an air compressor.

Another factor to consider is what you will be using the compressor for and how much air pressure you will need. If your industrial or manufacturing facility operates high-powered machinery that requires large amounts of air over extended periods of time, a two-stage air compressor will be the better option. If your machinery requires less air pressure over short periods of time, a single-stage air compressor will meet your needs.

Generally, if your machinery or tools require less than 100 PSI, a single-stage air compressor offers adequate air pressure to power your operations. However, if you operate large-scale machinery requiring more than 100 PSI, you will need a two-stage air compressor to provide adequate power.

Explore Our Selection of Air Compressors

Deciding between a single-stage and a two-stage air compressor depends on various factors. The most important is how much air you need and how frequently you need it to operate your tools or machinery. Whether you are looking for a single-stage or two-stage type, Fluid-Aire Dynamics offers a wide variety of air compressors to meet your needs.

Our quality air compressors are energy-efficient for an excellent return on investment. We also offer 24/7 emergency service for around-the-clock access to equipment repair services to reduce machinery downtime.

When you purchase an air compressor from Fluid-Aire Dynamics, you can expect excellent customer service, superior system design and post-sale support. Pennsylvania is our main location, but our air compressor sales and service experts extend sales, emergency services and preventative maintenance to the Maryland, Delaware, Northern Virginia and New Jersey areas. Contact us to learn more about our large selection of air compressors.

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