Five Things To Know About Single Acting Reciprocating Compressors

With the development of highly efficient air compressors, there’s still a place for the most basic design: the single acting reciprocating compressor.  When the piston moves out of the cylinder, it draws air in, at atmospheric pressure.  When it moves in to the cylinder, it reduces the volume that air occupies, increasing its pressure.  These machines are durable, effective, relatively inexpensive, and pretty easy to maintain.  Here are a few interesting things to know about them:

1. Popularity. Because of the simplicity of their design, they’re the most common air compressor in the 10HP and under sizes.  You can get them from a number of sources, and they’re not going to set you back as much as some other types.
2. Oil free air (part 1) While the most basic design uses oil to lubricate the piston rings in the compression cylinder, oil-less reciprocating compressors have cylinders with very smooth (and hard) bore surfaces, like nickel or chrome plating. A series of guide rings around the whole circumference of the piston prevent metal-to-metal contact, eliminating the need for liquid lubrication in the compression cylinder.
3. Oil free air (part 2) If oil in your compressed air is a problem, an oil-free (as opposed to oil-less) compressor is another option. While an oil-less compressor doesn’t use lubricant for the piston movement, an oil-free compressor’s moving parts are oil lubricated, but that oil is kept away from the compression cylinder(s) with connecting rod(s) so that the oil is confined to the lower moving parts…the crankshaft and bottom ends of the connecting rods, and away from the pistons & compression cylinders.
4. Foundation. Reciprocating machinery, as the name implies, has parts that move back and forth. The sudden reversal of direction of heavy metal pistons & rods, dozens of times a minute, means that their operation is inherently unbalanced. This out-of-balance condition, though, can be absorbed by properly securing the compressor to a properly prepared foundation.
5. Higher pressures. If your facility’s compressed air usage primarily entails pneumatic tools, cylinders, and blow off devices like air guns, the system header pressure is likely maintained at around 100psig. While a one-stage reciprocating compressor is usually rated for discharge pressures up to 125psig, a second stage can increase that to 175psig. Multi-stage compressors are used for applications that require up to 3,000psig compressed air. Examples of these are scuba breathing air, pneumatic excavators, and my personal favorite: ballast tank blowing air, used to surface a submarine.

4-stage reciprocating compressors charge 3,000psig air tanks that are used to rapidly push water from a submarine’s ballast tanks to create positive buoyancy.  Because keeping your ‘diving-to-surfacing’ ratio at 1:1 is important.

At EXAIR Corporation, helping you get the most out of your compressed air system is important to us.  If you’ve got questions about how to do just that, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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Compressed Air Receiver Tanks On The “Demand” Side

Most any air compressor is going to have a receiver tank…from the “pancake” types that might hold a gallon or so, to the large, multi-tank arrangements that facilitate both cooling and drying of compressed air in major industrial installations.  The primary purpose of these receiver tanks is to maintain proper operation of the compressor itself…they store a pressurized volume of air so that the compressor doesn’t have to run all the time.  Receiver Tanks, however, can also be used to eliminate fluctuations at points of use, especially in facilities where there might be a lot of real estate between the compressor and the compressed air consuming products.

I recently had the pleasure of discussing an Line Vac Air Operated Conveyor application with a caller.  The need was to move wood chips, from inside to outside the plant, into trailers.  The facility has plenty of compressed air to operate the Line Vacs (the application calls for several) but because the point of operation is so far from the header, they’ll need a “stash” (the caller’s words…we call it “intermediate storage” but he’s not wrong) of compressed air to keep the Line Vacs supplied for operation without any dips in performance.

Enter the Model 9500-60 60 Gallon Receiver Tank.  When an application requires an intermittent demand for a high volume of compressed air, the Receiver Tank provides intermediate storage (or a “stash” – that word’s growing on me) to prevent pressure fluctuations and the associated dips in performance.

Model 9500-60 60 Gallon Receiver Tank

The Model 9500-60 has a small footprint for where floor space is at a premium, and meets ASME pressure vessel code specifications. It comes with a drain valve so you can discharge condensate and contaminants.  A check valve (not included) can be installed upstream to maintain the tank at max pressure so it doesn’t ‘back feed’ other upstream uses.

Use of intermediate storage near the point of use is one of our Six Steps To Optimizing Your Compressed Air System.  If you’d like to find out more about getting the most out of your compressed air, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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Pressure – Absolute, Gauge, and Units of Both

Compressed air is a common utility used throughout industrial facilities and it has to be measured like any other utility in order to know just how much a facility is using. When dealing with compressed air a common unit of measurement that readily comes up is psi, pound-force per square inch. This unit of measure is one of the most basic units used to measure pressure in the compressed air industry. There are other means to measure this though, so let’s discover the difference.

Again, the pressure is a force distributed over an area, the Earth’s atmosphere has pressure, if it didn’t we would all balloon up like the Violet from Willy Wonka, just without eating some prototype gum causing internal pressure. PSIA is a unit of measure that is relative to a full vacuum. It is pounds per square inch absolute (PSIA). The absolute pressure is calculated as the sum of the gauge pressure plus the atmospheric pressure. If you were to travel into space, the atmospheric pressure would be absolute zero which is actually a vacuum. There is nothing pushing from the outside in so the inside pushes out, hence the ballooning.

The atmospheric pressure on earth is based on sea level. This is 14.7 pounds per square inch absolute pressure. This pressure will change along with the weather and the altitude at which the measurement is taken.

So how do we get to the pressure that is displayed on a pressure gauge?  When shown open to room air, my pressure gauge reads zero psi. Well, that is zero psi gauge, this already has the atmosphere showing. It is not showing the Absolute pressure, it is showing the pressure relative to atmospheric conditions. This is going back to the fact that gauge pressure is the summation of absolute pressure and atmospheric conditions, for sea level on earth that is 14.7 psia. So how do we increase this and get the gauge to read higher levels?

We compress the air the gauge is measuring, whether it is using a screw compressor, dual-stage piston compressor, single-cylinder, or any other type of compressor, it is compressing the ambient, atmospheric air. Some materials do not like being compressed. Air, however, reacts well to being compressed and turns into a form of stored energy that gets used throughout industrial facilities.  By compressing the air, we effectively take the air from atmospheric conditions and squeeze it down into a storage tank or piping where it is stored until it is used. Because the air is being compressed you can fit larger volumes (cubic feet or cubic meters) into a smaller area. This is the stored energy, that air that is compressed always wants to expand back out to ambient conditions. Perhaps this video below will help, it shows the GREAT Julius Sumner Miller explaining atmospheric pressure, lack of it, and when you add to it.

Lastly, no matter where you are, there is a scientific unit that can express atmospheric pressure, compressed air pressure, or even lack of pressure which are vacuum levels. To convert between these scientific units, some math calculations are needed. While the video below is no Julius Sumner Miller, it does a great job walking through many of the units we deal with daily here at EXAIR.

 

If you want to discuss pressures, atmospheric pressure, how fast the air expands from your engineered nozzle to atmospheric, why all the moisture in the air compresses with it, and how to keep it out of your process, contact an application engineer and we will be glad to walk through the applications and explanations with you.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

1 – Willy Wonka & the Chocolate Factory – Violet Blows Up Like a Blueberry Scene (7/10) | Movieclips, Movieclips, retrieved from https://youtu.be/8Yqw_f26SvM

2 – Lesson 10 – Atmospheric Pressure – Properties of Gases – Demonstrations in Physics,  Julius Sumner Miller, Retrieved from https://www.youtube.com/watch?v=P3qcAZrNC18

3 – Pressure Units and Pressure Unit Conversion Explained, Chem Academy, retrieve from https://www.youtube.com/watch?v=2rNs0VMiHNw

 

Compressor Room Updates Improve Performance

I’d like to start out by saying a common theme I have observed over the past six months is a huge spike in DIY projects around the home. While everyone has been sent home to work and kids have been sent home to learn remotely, the home has become more than just a resting place. It is an office, school, recreation center, even movie theater. This led to an amazing year for home improvement big box stores and lots of people are tackling projects that they may have thought were beyond their level. At this point in the year we are also seeing a lot of manufacturing that either hasn’t stopped or is starting back up safely, there are lots of projects around an industrial facility that can be tackled during downturns as well.

Compressor Room – 1

The main focus today will be on a critical room that generally gets shoved back into a deep dark corner, the compressor room. The air compressor is a piece of capital equipment that generates a companies 4th utility, compressed air. This is then sent throughout most of the facility and utilized at critical points within production. Air compressors have changed their look over the years and are still often crammed into a small dimly lit room that no one wants to venture into. Having an outdated compressor room can also be causing undesirable performance and lack luster performance as well. Here’s a few items that can more often than not be addressed pretty simply to improve the overall appearance and most importantly the performance of the compressors.

Clean air intake on a screw compressor – 2

First, clean air intake. Rather than letting the compressor suck air in from the room that may be stagnant or even worse, just sucking in the hot air coming off the heat exchangers on the compressor and causing elevated compressed air temps. This fix can include ducting clean air from outside of the facility to ensure micro-debris from within the facility isn’t being pulled in. While pulling in ambient air from outside the facility will still require a filter that will need to be maintained. If a large single source is used, that is perfectly acceptable. To step this project up multiple smaller inlets that are each controlled by a damper would permit variability to match ambient conditions on temperature.

Industrial exhaust fan – 3

Second, install an exhaust fan that feeds the air not just out of the room, yet out of the facility if at all possible. This helps to promote a through-flow of air with the clean air intake and keep from recirculating dirty already cycled air. This will also help any form of system based air treatment that relies on an exchange of heat, such as a refrigerant dryer. Again, a fan that stays on constantly would be the base level fix, step this up by adding a thermostatically controlled system so the fan doesn’t run continuously.

Third, if you heat your facility throughout the winter, use that hot exhaust air from the compressors to reclaim the heat of the compression cycle and optimize your return on using electricity. This can be done by strategic routing of the exhaust ductwork mentioned above, and can be stepped up to have thermostatically controlled dampers on the ducts to open and flow the air through an adjacent room for cooler months rather than exhaust straight out during the warm Summer months.

If you would like to discuss any of these topics or any of your compressed air point of use applications, feel free to contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

 1 – Air Compressor in Engine Room – retrieved from, Work With Sounds / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0) – https://commons.wikimedia.org/wiki/File:Air_compressor_in_engine_room.JPG

2 – Screw Compressor 1 – retrieved from, Endora6398 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0) – https://commons.wikimedia.org/wiki/File:Screw_compressor_1.jpg

3 – Industrial Exhaust Fan – retrieved from , Saud / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0) – https://commons.wikimedia.org/wiki/File:Industrial_Exhaust_Fan.jpg