Tag: 9500-60

Intelligent Compressed Air®: Compressor Motors And Controls

Published on by Russ BowmanLeave a comment

Use of compressed air has gone hand in hand with manufacturing for centuries. From manually operated bellows devices that stoked fires to generate the high temperatures needed for forging metals in ancient times, to the massive steam or oil driven compressors used in the 1800’s on projects like the Mont Cenis Tunnel drills, to the sophisticated electric-powered compressors used widely across modern industry, compressed air has actually been “the fourth utility” longer than the other three (electricity, gas, and water) have been in existence.

Diesel & gas powered compressors offer advantages like higher power ratings, portability, and freedom from reliance on local electric power grids, but most air compressors in industrial use are powered by electric motors. They’re plentiful, reliable, and easily adaptable to a range of control schemes that offer efficient operation across a wide variety of operations.

Which control method is right for you will depend on a number of factors specific to your operation. Here’s a brief run-down that may help you narrow down the selection:

  • Compressors in smaller facilities that supply intermittent loads like air guns, paint sprayers, tire inflators, etc. (like the one shown on the right) are oftentimes controlled via Start/Stop. This turns the compressor motor on and off, in response to a pressure signal. This is the simplest, least expensive method, and is just fine for smaller reciprocating compressors that aren’t adversely affected by cycling on & off.
  • Some compressors ARE adversely affected by Start/Stop control…like rotary screw models. These take a finite amount of time to start back up, which could allow header pressure to drop below usable levels. If they cycle too often, heat from the starting current can build up & overheat the motor. If that’s not bad enough, the screw elements & bearings of the compressor itself are oil lubricated…every time they start up, there’s a finite amount of time where metal-to-metal contact occurs before the oil flow is providing rated lubrication. With Load/Unload control, the motor turns continuously, while a valve on the intake of the compressor is cycled by the compressor discharge pressure: it opens (loads) to build or maintain pressure, and closes (unloads) when rated pressure is achieved. When unloaded, the motor uses about 1/3 of the energy it uses while loaded.
  • While turning down energy use to 1/3 of full load is a great way to cut operating cost while maintaining operational integrity of your compressed air system, and physical integrity of your compressor, it doesn’t necessarily make sense when demand may be low enough to be serviced by existing system storage over long periods of time. That’s where Dual/Auto Dual control comes in. It allows you to select between Start/Stop and Load /Unload control modes.  Automatic Dual Control incorporates an over-run timer, so that the motor is stopped after a certain period of time without a demand. This method is most often used in facilities where different shifts have substantially different compressed air load requirements.

When any of the above control schemes are used, they will necessarily rely on having an adequate storage capacity…the compressor’s receiver, and intermediate storage (like EXAIR’s Model 9500-60 60 Gallon Receiver Tank, shown on right) must be adequately sized (and strategically located) to ensure adequate point-of-use pressures are maintained while the compressor’s motor or intake valve cycle. Other methods use variable controls to “tighten up” the cycle bands…these don’t rely on as much storage volume, and in some (but not all) cases, result in higher energy efficiency:

  • A variation of Load/Unload control, called Modulation, throttles the intake valve instead of opening & closing it, to maintain a specific system pressure. This method is limited in range from 100% to 40% of rated capacity, though, so it’s fairly inefficient in many cases.
  • Slide, spiral, or turn valves are built in to certain compressor designs to control output by a method called Variable Displacement, which (as advertised) changes the physical displacement volume of the air end. When header pressure rises, it sends a signal which repositions the valve progressively, reducing the working length of the rotors. This allows some bypass at the inlet, limiting the volume of air that’s being compressed with each turn of the rotor. Since the inlet pressure & compression ratio remain constant, the power draw from the partial load is considerably lower…so it costs less to operate. The normal operating range for this method is from 100% to 40% of rated capacity, but when used in conjunction with inlet valve Modulation, it’s effective & efficient down to 20% of rated capacity.
  • Of course, the most significant advance in efficient control of rotating industrial equipment since Nikola Tesla invented 3-phase AC is the Variable Speed Drive. When the frequency of the AC power supplied to an electric motor is changed, the speed at which it rotates changes in direct proportion. By applying this type of control to an air compressor, the motor’s speed is continuously controlled to match the air demand. Energy costs can be greatly reduced, as this method allows efficient turn down to as low as 20% of rated capacity.

As mentioned a couple times above, multiple control schemes can be applied, depending on user specific needs. Adding accessories, of course, adds cost to your capital purchase, but discussions with your air compressor dealer will lay out the pros, cons, and return on investment. While we don’t sell, service, or even recommend specific air compressors, EXAIR Corporation is in the business of helping you get the most out of your compressed air system. If you’d like to talk more about it, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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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

How-To Size Receiver Tanks and Why Use Them in Your Compressed Air System

Published on by johnball2014Leave a comment
Receiver Tank

My colleague, Lee Evans, wrote a blog about calculating the size of primary receiver tanks within a compressed air system.  (You can read it here: Receiver Tank Principle and Calculations).  I would like to expand a bit more about secondary receiver tanks.  They can be strategically placed throughout the plant to improve the operation of your compressed air system.  The primary receiver tanks help to protect the supply side when demands are high, and the secondary receiver tanks help pneumatic systems on the demand side for optimum performance.

Circuit Board

I like to compare the pneumatic system to an electrical system.  The receiver tanks are like capacitors.  They store energy produced by an air compressor like a capacitor stores energy from an electrical source.  If you have ever seen an electrical circuit board, you notice many capacitors with different sizes throughout the circuit board (reference photo above).  The reason for this is to have a ready source of energy to increase efficiency and speeds with the ebbs and flows of electrical signals.  The same can be said for a pneumatic system with secondary receiver tanks.

To tie this into the compressed air system, if you have an area that requires a high volume of compressed air intermittently, a secondary receiver tank would benefit this type of pneumatic setup.  With valves, cylinders, actuators, and pneumatic controls which turn on and off, it is important to have a ready source of stored “energy” nearby.

For calculating a minimum volume size for your secondary receiver tank, we can use Equation 1 below.  It is the same for sizing a primary receiver tank, but the scalars are slightly different.  The supply line to this tank will typically come from a header pipe that supplies the entire facility.  Generally, it is smaller in diameter; so, we have to look at the air supply that it can feed into the tank.  For example, a 1” NPT Schedule 40 Pipe at 100 PSIG can supply a maximum of 150 SCFM of air flow.  This value is used for Cap below.  C is the largest air demand for the machine or targeted area that will be using the tank.  If the C value is less than the Cap value, then a secondary tank is not needed.  If the Cap is below the C value, then we can calculate the smallest tank volume that would be needed.  The other value in the equation is the minimum tank pressure.  In most cases, a regulator is used to set the air pressure for the machine or area.  If the specification is 80 PSIG, then you would use this value as P2.  P1 is the header pressure that will be coming into the secondary tank.  With this collection of information, you can use Equation 1 to calculate the minimum tank volume.  So, any receiver tank with a larger volume would work as a secondary receiver tank.

Equation 1:

V = T * (C – Cap) * (Pa) / (P1-P2)

Where:

V – Volume of receiver tank (cubic feet)

T – Time interval (minutes)

C – Air demand for system (cubic feet per minute)

Cap – Supply value of inlet pipe (cubic feet per minute)

Pa – Absolute atmospheric pressure (PSIA)

P1 – Header Pressure (PSIG)

P2 – Regulated Pressure (PSIG)

If you find that your pneumatic devices are lacking in performance because the air pressure seems to drop during operation, you may need to add a secondary receiver to that system.  EXAIR stocks 60 Gallon tanks, model 9500-60, to add to those specific areas.  If you have any questions about using a receiver tank in your application, primary or secondary, you can contact an EXAIR Application Engineer.  We can restore your efficiency and speed back into your applications.

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

Photo: Circuit Board courtesy from T_Tide under Pixabay License