When it comes to generating compressed air there are many types of compressors to utilize within a facility. One of those types is a dual acting reciprocating compressor. This is a type of positive displacement compressor that takes advantage of a piston style action and actually compresses air on both directions of the stroke. Below you can see a video from a company that showcases how a dual acting compressor works and gives a good representation of how it is compressing the air on both directions of travel.
The reciprocating type of air compressor uses a motor that turns a crank which pushes a piston inside a cylinder; like the engine in your car. In a basic cycle, an intake valve opens to allow the ambient air into the cylinder, the gas gets trapped, and once it is compressed by the piston, the exhaust valve opens to discharge the compressed volume into a tank. This method of compression happens for both the single and double acting reciprocating compressors.
With a single acting compressor, the air is compressed only on the up-stroke of the piston inside the cylinder. The double acting compressor compresses the air on both the up-stroke and the down-stroke of the piston, doubling the capacity of a given cylinder size. This “double” compression cycle is what makes this type of air compressor very efficient. A single acting compressor will have an operating efficiency between 100 cfm / 23 kW of air while the double acting compressor has an operating efficiency between 100 cfm 15.5 kW . Therefore, electricity cost is less with a double-acting reciprocating air compressor to make the same amount of compressed air.
These compressors are ruggedly designed to be driven 100% of the time and to essentially be a Clydesdale of compressors. They are commonly used with applications or systems requiring higher pressures and come in lubricated or non-lubricated models.
If you would like to discuss air compressors or how to efficiently utilize the air that your system is producing so that you aren’t giving your compressor an artificial load that isn’t needed, contact us.
Evaluating all of the different types of compressors and which is right for you can seem like a daunting task. Today, I’d like to take some time to talk about the Double-Acting Reciprocating type of air compressor.
Double-Acting Reciprocating compressors are a subset of the larger family of positive displacement compressor types. In positive displacement compressors, air is drawn into a chamber where the volume is then mechanically reduced. The energy used to displace the air volume is converted to an increase in air pressure. Dynamic compressors operate a little differently. They utilize an increase in air velocity to create the change in pressure. Air is accelerated to a high velocity through an impeller. The kinetic energy of the air is converted to an increase in potential (pressure) energy.
The Double-Acting Reciprocating compressor is a close relative to the Single-Acting Reciprocating compressor. In these types of compressors, an “automotive-type” piston driven by a crankshaft provides the compression. In a Double-Acting Reciprocating compressor, air is compressed as the piston moves in each direction. Hence the name, “double-acting”. In a Single-Acting Reciprocating compressor, air is only compressed on each full revolution of the piston. This makes the Double-Acting Reciprocating compressor much more efficient than its brethren.
Double-Acting Reciprocating compressors are also available in much larger sizes. While Single-Acting compressors can be found up to 150HP, generally they’re much less common any larger than 25HP. Whereas a Double-Acting compressor is available from 10HP-1,000HP, making it a better choice for larger plants that require a significantly greater volume of compressed air. While they’re a bit more expensive due to the added mechanisms to produce the double-action compression, this cost is quickly offset by the increase in efficiency. At a performance of 15-16 kW/100 cfm, they’re 32% more efficient than a single-acting reciprocating compressor.
If you’re in the market for a new compressor and are struggling to determine the most suitable compressor, talk with your local compressor sales representative. Once you’re up an running, EXAIR has a wide-range of products that’ll make sure you’re using your compressed air safely and efficiently!
Of all the types of air compressors on the market, you can’t beat the single acting reciprocating air compressor for simplicity:
This simplicity is key to a couple of major advantages:
Price: they can cost 20-40% less than a similar rated (but more efficient) rotary screw model, up to about 5HP sizes. This makes them great choices for home hobbyists and small industrial or commercial settings.
High pressure: It’s common to see reciprocating compressors that are capable of generating up to 3,000 psig. Because the power is transmitted in the same direction as the fluid flow, they can handle the mechanical stresses necessary for this much better than other types of air compressors, which may need special modifications for that kind of performance.
Durability: out of necessity, their construction is very robust and rugged. A good regimen of preventive maintenance will keep them running for a good, long time. Speaking of which…
Maintenance (preventive): if you change your car’s oil and brake pads yourself, you have most of the know-how – and tools – to perform regular upkeep on a reciprocating air compressor. There’s really not that much to them:
Those advantages are buffered, though, by certain drawbacks:
Efficiency, part 1: The real work (compressing the air) only happens on the upstroke. They’re less efficient than their dual acting counterparts, which compress on the downstroke too.
Efficiency, part 2: As size increases, efficiency decreases. As stated above, smaller sizes usually cost appreciably less than more efficient (rotary screw, vane, centrifugal, etc.) types, but as you approach 25HP or higher, the cost difference just isn’t there, and the benefits of those other types start to weigh heavier in the decision.
Maintenance (corrective): Whereas they’re easy to maintain, if/when something does break, the parts (robust and rugged as they are) can get pretty pricey.
Noise: No way around it; these things are LOUD. Most of the time, you’ll find them in a remote area of the facility, and/or in their own (usually sound-insulated) room.
High temperature: When air is compressed, the temperature rises due to all the friction of those molecules getting shoved together…that’s going to happen with any air compressor. All the metal moving parts in constant contact with each other, in a reciprocating model, add even more heat.
Oil in the air: If you’re moving a piston back & forth in a cylinder, you have to keep it lubed properly, which means you have oil adjacent to the air chamber. Which means, no matter how well it’s built, you’re likely going to have oil IN the air chamber.
All that said, the benefits certainly do sell a good number of these compressors, quite often into situations where it just wouldn’t make sense to use any other type. If you’re in the market for an air compressor, you’ll want to find a local reputable air compressor dealer, and discuss your needs with them. If those needs entail the use of engineered compressed air products, though, please feel free to give me a call to discuss. We can make sure you’re going to ask your compressor folks the right questions.
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One thing that is found in virtually every industrial environment is an air compressor. Some uses for the compressed air generated are: powering pneumatic tools, packaging, automation equipment, conveyors, controls systems, and various others. Pneumatic tools are favored because they tend to be smaller and more lightweight than electric tools, offer infinitely variable speed and torque, and can be safer than the hazards associated with electrical devices. In order to power these devices, compressed air must be generated.
There are two main categories of air compressors: positive-displacement and dynamic. In a positive-displacement type, a given quantity of air is trapped in a compression chamber. The volume of which it occupies is mechanically reduced (squished), causing a corresponding rise in pressure. In a dynamic compressor, velocity energy is imparted to continuously flowing air by a means of impellers rotating at a very high speed. The velocity energy is then converted into pressure energy.
Of the positive-displacement variety they are broken down further into two more categories: reciprocating and rotary. A reciprocating compressor works like a bicycle pump. A piston reduces the volume occupied by the air or gas, compressing it into a higher pressure. There are two types of reciprocating compressors, single or double-acting. Single-acting compressors are the most common and are available up to 30HP at 200 psig. Their small size and weight allow them to be installed near the point of use and avoid lengthy piping runs. These are the types of compressors that would be commonly found in your garage. The double-acting reciprocating compressor is much like its single-acting brethren, only it uses both sides of the piston and cylinder for air compression. This doubles the capacity of the compressor for a given cylinder size. They are much more efficient than single-acting compressors, but are more expensive and do require a more specialized installation and maintenance.
Rotary compressors are available in lubricant-injected or lubricant-free varieties. These types of compressors use two inter-meshing rotors that have an inlet port at one end and a discharge port at the other. Air flows through the inlet port and is trapped between the lobes and the stator. As the rotation continues, the point intermeshing begins to move along the length of the rotors. This reduces the space that is occupied by the air, resulting in an increase in pressure. In the lubricant-injected compressors, the compression chamber is lubricated between the intermeshing rotors and bearings. This takes away the heat of compression and also acts as a seal. In the lubricant-free varieties, the intermeshing rotors have very tight tolerances and are not allowed to touch. Since there is no fluid to remove the heat of compression, they typically have two stages of compression with an intercooler between and an after cooler after the second stage. Lubricant-free compressors are beneficial as they supply clean, oil-free compressed air. They are, however, more expensive and less efficient to operate than the lubricant-injected variety.
On the other side of the coin, we have the dynamic compressors. These are comprised of two main categories: axial and centrifugal. These types of compressors raise the pressure of air or gas by imparting velocity energy and converting it to pressure energy. In a centrifugal air compressor, air continuously flows and is accelerated by an impeller. This impeller can rotate at speeds that exceed 50,000 rpm. Centrifugal air compressors are generally much larger and can accommodate flow ranges of 500-100,000 CFM. They also provide lubricant-free air.
Axial compressors are used for situations that require lower pressure but high flow rates. They do not change the direction of the gas, it enters and exits the compressor in an axial direction. It is accelerated and then diffused which creates the increase in pressure. A common application that would be served by this type of compressor is to compress the air intake of gas turbines. They have a relatively high peak efficiency, however their large overall size and weight as well as the high starting power requirements pose some disadvantages.
Just as you can find a wide variety of makes and models of automobiles, the same can be said for air compressors. The size, type, and features will be dictated by the types of applications that you’ll be needing the compressed air for in your facility. A quick chat with your local air compressor supplier will help you to determine which type is most suitable for you.
Of course, any of these types of compressors can be used to supply air to your engineered Intelligent Compressed Air Products. If you have an application in your facility that could benefit from an engineered solution, give us a call. An Application Engineer would be happy to discuss your options with you and see to it that you’re getting the most out of your compressed air!