Tag: supply & demand

Basics of the Compressed Air System

Published on by John BallLeave a comment

Compressed air is used to operate pneumatic systems within a facility, and it can be separated into three categories; the supply side, the demand side, and the distribution system.  In this blog, I will cover each area. 

The supply side is the air compressor, after-cooler, dryer, and receiver tank that produce and treat the compressed air.  They are generally located in a compressor room somewhere in the corner of the plant.  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 pressure and the amount of air that needs to be compressed. 

The demand side is the collection of devices that will use that compressed air to do “work”.  These pneumatic components are generally scattered throughout the facility.  This would include valves, cylinders, blow-offs, pneumatic clamps, etc.   To condition the demand side, regulators and filters are used.  The Pressure Regulators help to limit the amount of pressure.  For blow-off devices, the lower the air pressure to “do the job”, the less compressed air is used.  To help with the fluctuations in demand, a secondary Receiver Tank can be used.  The demand side can also be a system to do specific jobs. In using pneumatic systems, the “power” must come from the supply side. 

To connect the supply side to the demand side, a compressed air distribution system is required.  Distribution systems are pipes which carry the compressed air from the compressor to the pneumatic devices.  For a sound compressed air system, the three sections have to work together to make an effective and efficient system. An analogy that I like to use is to compare the compressed air system to an electrical system.  The air compressor would be considered the voltage source, and the pneumatic devices would be considered as light bulbs.  To connect the light bulbs to the voltage source, electrical wires are needed which will represent the distribution system.  If the gauge of the wire is too small to supply the light bulbs, the wire will heat up and a voltage drop will occur.  This heat is given off as wasted energy, and the light bulbs will be dim.  The same thing happens within a compressed air system.  If the piping size is too small, a pressure drop will occur.  This is also wasted energy.  In both types of systems, wasted energy is wasted money.  One of the largest systematic problems with compressed air systems is pressure drop.  With a properly designed distribution system, energy can be saved, and, in reference to my analogy above, it will keep the lights on.  To have a properly designed distribution system, the pressure drop should be less than 10% from the reservoir tank to the point-of-use.

Processes lead to continuous improvement.

EXAIR created the “Six Steps to Optimizing Your Compressed Air System”.  By following these tips, you can have the supply side, demand side, and distribution system working at peak efficiency.  If you would like to reduce waste even more, EXAIR offers a variety of efficient, safe, and effective compressed air products to fit within the demand side.  This will include the EXAIR Super Air Knives, Super Air Nozzles, and Safety Air Guns.  This would be the electrical equivalent of changing those incandescent light bulbs into LED light bulbs.  If you wish to go further in enhancing your system, an Application Engineer at EXAIR will be happy to help you. 

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

Photo:  Lightbulb by qimono.  Pixabay Licence

Compressed air Storage: Do you need a Receiver Tank?

Published on by Jordan T ShouseLeave a comment

Maintaining a “supply and demand” balance in the design & operation of compressed air systems often includes receiver tanks.

Just like in economics, we have to consider both sides – supply AND demand – to best maintain this balance.  Also like in economics, there are numerous factors…on both sides…but the two most critical factors are:

  • Compressor capacity control (supply side)
  • System storage (demand side)

I wrote a blog on “Air Compressor Motors and Controls, Working Together”, outlining the ‘supply side’ variables, today lets look at the system storage. Distribution piping makes up a certain amount of this, and another great blog from my colleague, Tyler Daniel – “Intelligent Compressed Air: Distribution Piping and Pressure Drop” – gets me off the hook for THAT part of the discussion today.

We can consider the air capacity of system piping to be fixed for the purposes of this discussion, so our “variable” will be the capacity of storage tanks. Let’s start with the reasons for the need for system storage: Strategically placed point-of-use air receivers provide stored energy for intermittent demands.  This enables the compressed air system to handle fluctuating loads, efficiently & reliably.  It also minimizes impact (e.g., sudden and often detrimental drops) on the system pressure.

Next, we’ll look at location. There are a couple of common options to consider:

  • The intermittent demand. Installing a receiver here will provide enough air for short duration, high consumption events, protecting the rest of the system from pressure excursions. Dedicating the receiver to this application will mean isolating it from the rest of the system with a check valve (so it only supplies the load in question) and a needle valve (so recharging the receiver itself, between the intermittent uses, doesn’t adversely affect total system pressure).
  • The critical load(s). Instead of using stored air for the intermittent load, you can also use it for the important loads you’re trying to protect. All sorts of machinery with pneumatic components can “crash” if a nearby intermittent demand starts up & “steals” their air. You’ll use a check valve (same as above), but using a needle valve to throttle the air flow that recharges the receiver risks “starving” the critical load. Don’t do that unless there’s a really good (and likely really specific) reason for it.

Finally, we’re going to do some math, so we know how big this receiver has to be. Here’s the equation we use to do that:

Let’s calculate the receiver size needed to supply an intermittent load of 400 SCFM (C) @80psig (P2), that’ll run for one minute (T). You can use data specific to your system to come up with a value for (Cap) but here I’m going to assume we want the receiver to be able to handle the whole thing, so Cap = 0. I’m also going to assume we’re at sea level, so Pa = 14.7psia and that our compressor’s discharge pressure (the pressure at which the receiver can be charged to) is 120psig (P1):

That’s an awfully big tank. Now, let’s calculate the receiver size needed to protect a critical load that uses 55 SCFM @60psig, and that due to the system design, we can count on 25 SCFM @120psig from the compressor:

This is a much more manageable size, in fact, our 60 Gallon Receiver Tank (Model 9500-60) would be ideal. It’s 20″ in diameter and just over 50″ tall, so it doesn’t take up a lot of floor space. It comes with a drain valve and connections for compressed air flow in & out, pressure gauge, relief valve, etc.

Step Five of our Six Steps To Optimizing Your Compressed Air System: Use intermediate storage near the point of use.

Now, the above example is a completely hypothetical situation, and I purposely chose exaggerated values to show that there can indeed be a clear “winner” in the choice between the two installation points. If you have a situation like this, and would like help in finding the solution that makes the most sense, give us a call.

Jordan Shouse
Application Engineer

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How To Determine The Need For – And The Size Of – Compressed Air Receiver Tanks

Published on by Russ BowmanLeave a comment

Supply and Demand, in economics, defines the relationship between the volume of commodities that sellers want to exchange for a certain amount of currency, and the volume of said commodities that buyers are willing to exchange a certain (and sometimes different) amount of currency for.  The best chance for an ideal condition is when the volume produced is the same as the volume being consumed.  That typically means both sides are amenable to the same certain amount of currency, and everyone’s happy: the sellers are making a fair profit, and the buyers are paying a fair price.  Thing is, that’s a difficult balance to maintain.  The reasons for imbalances are often debated and usually contentious, and I have no intention of going in to them here.  I only brought up the subject to draw an analogy to the difficulties in maintaining a “supply and demand” balance in the design & operation of compressed air systems.

Just like in economics, we have to consider both sides – supply AND demand – to best maintain this balance.  Also like in economics, there are numerous factors…on both sides…but the two most critical factors are:

  • Compressor capacity control (supply side)
  • System storage (demand side)

My colleague Jordan Shouse wrote an excellent blog on “Air Compressor Motors and Controls, Working Together”, outlining the ‘supply side’ variables, allowing me to concentrate my efforts today on system storage. Distribution piping makes up a certain amount of this, and another great blog from another colleague, Tyler Daniel – “Intelligent Compressed Air: Distribution Piping and Pressure Drop” – gets me off the hook for THAT part of the discussion today.

We can consider the air capacity of system piping to be fixed for the purposes of this discussion, so our “variable” will be the capacity of storage tanks. Let’s start with the reasons for the need for system storage: Strategically placed point-of-use air receivers provide stored energy for intermittent demands.  This enables the compressed air system to handle fluctuating loads, efficiently & reliably.  It also minimizes impact (e.g., sudden and often detrimental drops) on the system pressure.

Next, we’ll look at location. There are a couple of common options to consider:

  • The intermittent demand. Installing a receiver here will provide enough air for short duration, high consumption events, protecting the rest of the system from pressure excursions. Dedicating the receiver to this application will mean isolating it from the rest of the system with a check valve (so it only supplies the load in question) and a needle valve (so recharging the receiver itself, between the intermittent uses, doesn’t adversely affect total system pressure).
  • The critical load(s). Instead of using stored air for the intermittent load, you can also use it for the important loads you’re trying to protect. All sorts of machinery with pneumatic components can “crash” if a nearby intermittent demand starts up & “steals” their air. You’ll use a check valve (same as above), but using a needle valve to throttle the air flow that recharges the receiver risks “starving” the critical load. Don’t do that unless there’s a really good (and likely really specific) reason for it.

Finally, we’re going to do some math, so we know how big this receiver has to be. Here’s the equation we use to do that:

Let’s calculate the receiver size needed to supply an intermittent load of 400 SCFM (C) @80psig (P2), that’ll run for one minute (T). You can use data specific to your system to come up with a value for (Cap) but here I’m going to assume we want the receiver to be able to handle the whole thing, so Cap = 0. I’m also going to assume we’re at sea level, so Pa = 14.7psia and that our compressor’s discharge pressure (the pressure at which the receiver can be charged to) is 120psig (P1):

That’s an awfully big tank. Now, let’s calculate the receiver size needed to protect a critical load that uses 55 SCFM @60psig, and that due to the system design, we can count on 25 SCFM @120psig from the compressor:

This is a much more manageable size, in fact, our 60 Gallon Receiver Tank (Model 9500-60) would be ideal. It’s 20″ in diameter and just over 50″ tall, so it doesn’t take up a lot of floor space. It comes with a drain valve and connections for compressed air flow in & out, pressure gauge, relief valve, etc.

Step Five of our Six Steps To Optimizing Your Compressed Air System: Use intermediate storage near the point of use.

Now, the above example is a completely hypothetical situation, and I purposely chose exaggerated values to show that there can indeed be a clear “winner” in the choice between the two installation points. “Your mileage may vary,” as the car folks say. If you have a situation like this, and would like help in finding the solution that makes the most sense, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Cover image courtesy of: Tennessee Valley Authority; SVG version by Tomia, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons