Basics of Compressors

Single Stage Portable Air Compressor

What is an air compressor?  This may seem like a simple question, but it is the heartbeat for most industries.  So, let’s dive into the requirements, myths, and types of air compressors that are commonly used.  Like the name implies, air compressors are designed to compress air.  Unlike liquids, air is a compressible gas, which means that it can be “squished” into a smaller volume by pressure.  With this stored energy, it can do work for pneumatic systems.

There are two main types of air compressors, positive displacement and dynamic.  The core component of most air compressors is an electric motor that spins a shaft.  Positive displacement uses the energy from the motor and the shaft to change volume in an area, like a piston in a reciprocating air compressor or like rotors in a rotary air compressor.  The dynamic types use the energy from the motor and the shaft to create a velocity with an impeller like centrifugal air compressors.  This velocity converts to a rise in pressure.

How do they work?  Most air compressors are driven by an electric or gas motor.  The motor spins a shaft to push a piston, turn a rotor, or spin a vane.  At the beginning of the air compressor, we have the intake where a low pressure is generated from the displacement to bring in the surrounding ambient air.  Once trapped, Boyle’s law states that when the volume decreases, the pressure increases.  For the dynamic type, the velocity and design will increase the air pressure.  The higher pressure will then move to a tank to be stored for pneumatic energy.  The amount of power required is dependent on the amount of air that needs to be compressed. 

Compressed air is a clean utility that is used in many ways, and it is much safer than electrical or hydraulic systems.  But most people think that compressed air is free, and it is most certainly not.  Because of the expense, compressed air is considered to be a fourth utility in manufacturing plants.  For an electrical motor to reduce a volume of air by compressing it, it takes roughly 1 horsepower (746 watts) of power to compress 4 cubic feet (113L) of air every minute to 125 PSI (8.5 bar).  With almost every manufacturing plant in the world utilizing air compressors much larger than 1 horsepower, the amount of energy needed to compress a large volume of air is extraordinary.

Let’s determine the energy cost to operate an air compressor to make compressed air by Equation 1:

Equation 1:

Cost = hp * 0.746 * hours * rate / (motor efficiency)

where:

Cost – US$

hp – horsepower of motor

0.746 – conversion KW/hp

hours – running time

rate – cost for electricity, US$/KWh

motor efficiency – average for an electric motor is 95%.

As an example, a manufacturing plant operates a 100 HP air compressor in their facility.  The cycle time for the air compressor is roughly 60%.  To calculate the hours of running time per year, I used 250 days/year at 16 hours/day for two shifts.  So operating hours equal 250 * 16 * 0.60 = 2,400 hours per year.  The electrical rate at this facility is $0.10/KWh.  With these factors, the annual cost for operating the air compressor can be calculated by Equation 1:

Cost = 100hp * 0.746 KW/hp * 2,400hr * $0.10/KWh / 0.95 = $18,846 per year in just electrical costs.

So, what is an air compressor?  The answer is a pneumatic device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored as pressurized air.  Efficiency in using compressed air is very important.  EXAIR has been manufacturing Intelligent Compressed Air Products since 1983.  We are able to save you money by reducing the amount of compressed air you use.  If you need alternative ways to save money when you are using your air compressor, an Application Engineer at EXAIR will be happy to help you.  We even have a Cost Savings Calculator to find the annual savings and payback period; and you will be amazed at how much money can be saved. 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Photo: Technical Illustration of a portable single-stage air compressor by Brain S. Elliot.  Creative Commons CC BY-SA 4.0

Top Ten Reasons Why EXAIR’s Super Air Knife Is So Super

1. Efficiency – With an air entrainment ratio of 40:1 (literally means it pulls in 40 SCFM of “free” air from the surrounding environment for every 1 SCFM of consumption), compressed air consumption is dramatically lower than any other blow off device.

EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.

2. Laminar air flow – My colleague John Ball did a bang-up job in a video blog explaining the fluid mechanics theory behind this. Operationally, laminar flow is is beneficial because it’s particularly conducive to generating a stripping or sweeping action, as opposed to the turbulent flow from an open blow off, a blower, or a fan.

3. Quiet operation – The high entrainment ratio that makes the Super Air Knife so efficient also makes for amazingly low sound levels. The outermost entrained air creates a boundary layer that attenuates the sound level of the higher velocity, hard hitting center flow.

4. Lengths available – Super Air Knives are stocked in lengths from 3″ to 9ft. Custom lengths can be made if you’re space-limited for installation, and custom shims can be installed if you want to shorten the curtain width of a stock Super Air Knife. Super Air Knives can also be coupled together for even longer lengths.

Air Knife Coupling Bracket Kits are available from stock for Aluminum, 303SS, and 316SS Super Air Knives.

5. Material of construction – No matter how aggressive the environment is, odds are, EXAIR has a Super Air Knife that’ll hold up to it. Durable aluminum models are good to 180°F (82°C). There are also two Types of Stainless Steel to choose from: 303SS for high strength, and 316SS for protection from chloride pitting corrosion & higher strength. Both 303SS & 316SS are good to 800°F (427°C). For exceptionally harsh environments, PVDF (Polyvinylidene Fluoride) constructed Super Air Knives have Hastelloy C-276 hardware & PTFE shims, which are resistant to UV light, inorganic chemicals, solvents, ozone, weather, fungi, chlorinated hydrocarbons, highly corrosive acids, weak bases, and salts. They’re good to 275°F (135°C).

6. Easy installation – Like all of our products, the Super Air Knives – from the 3″ to the 9ft models – are “user friendly” as far as mounting & installation goes. The Model 9060 Universal Air Knife Mounting System makes for quick installation and easy positioning. 24″ to 42″ Super Air Knives need to be plumbed to both ends…if you hard pipe the air supply, the Super Air Knife itself will essentially be as well supported as the piping. The same holds true for longer Super Air Knives with Plumbing Kits installed. 3″ Super Air Knives can even be fitted with Stay Set Hoses, and Magnetic Bases. And the 1/4″-20 tapped holes on the bottom of the body allow for a wide range of mounting solutions…anything you can put a bolt through, really.

The 9060 Universal Air Knife Mounting Systems are perfect for simple, fast installation and positioning.
Yes, that’s a door hinge. No, it wasn’t my idea ( but I kind of wish it was.)

7. Low maintenance – With no moving parts, they’ll run darn near indefinitely, maintenance free, as long as you supply them with clean, moisture free compressed air. Oh, and keep them clean, externally, if they’re in an area where environmental contaminants can build up on the precision finished surfaces that are essential to their air entrainment.

8. Reliability – Hand in hand with #7, no moving parts also means there’s not much that can stop them from working. They can operate continuously, if needed, or you can cycle them on & off as frequently as necessary to keep from using valuable compressed air, except when needed.

EXAIR’s award winning EFC Electronic Flow Control can be set to operate a Super Air Knife (or any of our Intelligent Compressed Air Products) in cycles as low as 0.1 seconds.

9. Static Eliminator option -The laminar, high velocity air flow is ideal for many blow off applications, but if static charge is a problem, an Ionizing Bar can be installed, turning the Super Air Knife into a Super Ion Air Knife:

10. Free stuff – OK; this last one is “super” for a limited time. Order a Super Air Knife between 11/1/22 and 12/31/2022, and get a FREE Safety Air Gun. Click here for details.

If you’d like to find out how the Super Air Knife – or any of our Intelligent Compressed Air Products can help you get the most out of your compressed air system, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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What’s So Great About the EXAIR Sanitary Flange Line Vacs?

The greatness of EXAIR Line Vac Air Operated Conveyors can be summed up in a simple math(like) formula:

Line Vac + Hose or Pipe + Compressed Air = Instant Conveyor System

Today, dear reader, we’re going to explore the factors that contribute to the particular greatness of our Sanitary Flange Line Vacs:

Common industrial piping connections are difficult to sanitize, and offer ample breeding ground for bacteria.

Clean In Place capability. Many industrial fluid piping installations are made up of threaded or soldered connections, like those shown in the photo to the right. These products are easy to work with, readily available, and relatively inexpensive. They’re also unacceptable in facilities that require frequent cleaning to eliminate contamination – biological and otherwise – from their products & processes. Equipment in pharmaceutical, food production, and dairy farm facilities must be able to be sanitized effectively, so they’ll all use pipe & fittings that comply with specifications set forth in ISO Standard 2852 (Stainless steel clamp pipe couplings for the food industry) specifications for dimensions, surface roughness, materials, and assembly & hygienic requirements. While they’re known by a number of names – Tri-Clamp, Tri-Clover, S-Clamp, Sanitary, 3A, among others – they’re all aimed at compliance with ISO 2852. And EXAIR Sanitary Flange Line Vac products are compatible with any of them.

Sanitary Fittings come in number of configurations for quick & easy “making & breaking” for cleaning.

Diverse range of applications. While food & pharma are, by far, the main users, the ease of connection (and disconnection & reconnection), smooth ID specification for pipe, durability of stainless steel construction, and elimination of seams in fittings are all advantageous for other users as well:

  • A chemical company needed to remove long strands of cotton fiber away from a process, and convey it over a 60ft run to a scrap bin. The smooth ID of sanitary-grade stainless steel piping allows them to use a Model 161150-316 1-1/2″ Sanitary Flange Line Vac for reliable conveyance of this material, with no hang-ups or clogging in the long run of pipe.
  • An ammo manufacturer uses our Model 161200-316 2″ Sanitary Flange Line Vacs to convey small shell casings, in bulk from where they’re pressed, to where they’re loaded. They, too, like the smooth, seam-free pipe for conveyance, and the durability of all stainless steel construction. Another benefit is the quickness and ease of breaking & making the connections, as each Line Vac is used to convey these casings to multiple loading stations.
Sanitary Flange fittings make it easy to keep the inlet of this Model 161150-316 1-1/2″ Sanitary Flange Line Vac protected while not in use (left). The spring-loaded clamp makes it easy to swap out the cap for a barb fitting (middle) for use with a flexible suction hose (right).

Type 316 Stainless Steel Construction. Stainless Steel is specified for material construction for a number of reasons such as durability, aesthetics, and corrosion resistance. There are many alloys, and most will give you the smooth & shiny surface that folks think about when they think of stainless steel. Type 316, due to its hardness and particularly high resistance to chloride pitting corrosion, is extraordinarily popular in food & pharmaceutical application.

EXAIR Sanitary Flange Line Vacs come in four popular sizes, and are ideal for applications in the food and pharmaceutical industries…and others.

If you’ve got bulk material to move from “point A to point B”, EXAIR has a number of solutions to choose from. If you want to find out more, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Decibel Levels in Manufacturing

The Decibel (dB) is a unit used to measure the intensity of sound. Decibel levels are a little tricky as human ears are incredibly sensitive. Our ears can hear everything from a gnat flying by your ear to to very loud jet engines. The range of sound level is very vast. Manufacturing environments can be loud and expose employees to harmful noise levels. You can see some interesting manufacturing noise exposure data from the CDC, here.

On the decibel scale, the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB. Here are some common sounds and their decibel ratings:

Experience tells us that many things distance affects the intensity of sound. Noise levels can be due to product design, proximity to the noise, frequency of processes, quantity of noise producing machines or processes. Exposure to high noise levels can be harmful. Extended length of exposure to sound levels above above 80 dB can begin hearing loss. If you feel you have to raise the level of your voice to be heard then you can assume that you are in an environment of 85 or greater dB. OSHA Standard 29 CFR-1910.95 (a) shows the Maximum Allowable Noise Exposure.

EXAIR engineers our products with safety and exposure in mind and we manufacture most every product to be under any threshold where hearing protection is required. If any product (like our largest Super Air Nozzles) is above the threshold, EXAIR is clear that hearing protection is needed. Please visit www.EXAIR.com and view how our Intelligent Compressed Air Products can help your quality of work atmosphere. If you have any questions regarding our products or for advice as to what products can improve the safety of your work environment, please contact any one of our Application Engineers.

Eric Kuhnash
Application Engineer
E-mail: EricKuhnash@exair.com
Twitter: Twitter: @EXAIR_EK