## Air & Water DO Mix – Why That’s A Problem for Compressed Air Systems

Wherever you go, humidity – and its effects – are an inescapable fact of life. Low humidity areas (I’m looking at you, American Southwest) make for a “dry heat” in the summer that many prefer to the wet & muggy conditions that areas with higher humidity (like much of the rest of the United States) encounter during the “dog days” of summer.

Regardless of human comfort level issues, all atmospheric air contains water vapor in some finite proportion…in fact, next to nitrogen and oxygen, it makes up a bigger percentage of our air’s makeup than the next eleven trace gases combined:

And, because warmer air is capable of holding higher moisture concentrations (a 20°F rise in temperature doubles the potential for holding moisture), chances are good that it’ll become a bigger problem for your compressed air system in the summertime. So…how BAD of a problem is it? Let’s do some math. Consider a nice, typical summer day in the midwest, when it’s 80°F outside, with a relative humidity of 75% and we’ll use the data from the tables below to calculate how much water collects in the compressed air system:

Let’s assume:

• An industrial air compressor is making compressed air at 100psig, and at a discharge temperature of 100°F.
• The demand on the compressed air system (all the pneumatic loads it services) is 500 SCFM.

Table 3.3 tells us that, at 80°F and 75% RH, the air the compressor is pulling in has 0.1521 gallons per 1,000 cubic feet.

Table 3.4, tells us that, at 100°F and 100psig, the compressor is discharging air with a moisture content of 0.0478 gallons per 1,000 Standard Cubic Feet.

The difference in these two values is the amount of water that will condense in the receiver for every 1,000 SCF that passes through, or 0.1521-0.0478=0.1043 gallons. Since the demand (e.g., the air flow rate out of the receiver) is 500 SCFM, that’s:

500 SCFM X 60 min/hr X 8 hr/shift X 0.1043 gallons/1,000 SCF = 25 gallons of condensate

That’s 25 gallons that has to be drained from the receiver tank over the course of every eight hours, so a properly operating condensate drain is crucial. There are a few types to choose from, and the appropriate one is oftentimes included by the air compressor supplier.

So, you’ve got a condensate drain on your compressor’s receiver, and it’s working properly. Crisis averted, right? Well, not so fast…that 100°F compressed air is very likely going to cool down as it flows through the distribution header. Remember all that moisture that the hot air holds? Assuming the compressed air cools to 70°F in the header (a reasonable assumption in most industrial settings), a bunch of it is going to condense, and make its way to your air tools, cylinders, blow off devices, etc., which can cause a host of problems.

And…I trust you saw this coming…we’re going to calculate just how much condensation we have to worry about. Using table 3.4 again, we see that the header’s air (at 100psig & 70°F) can only hold 0.0182 gallons per 1,000 SCF. So, after cooling down from 100°F (where the air holds 0.0478 gallons per 1,000 SCF) to 70°F, that means 0.0296 gallons per 1,000 SCF will condense. So:

500 SCFM X 60 min/hr X 8 hr/shift X 0.0296 gal/1,000 SCF = 7.1 gallons of condensate

Qualified installers will have sloped the piping away from the compressor, with drip legs strategically placed at low points, so that condensate can drain, collect, and be disposed of…oftentimes via similar devices to the condensate drains you’ll find on the compressor’s main receiver. Good engineering practice, of course, dictates point-of-use filtration – EXAIR Automatic Drain Filter Separators, with 5-micron particulate elements, and centrifugal elements for moisture removal, are also essential to prevent water problems for your compressed air operated products.

EXAIR Corporation remains dedicated to helping you get the most out of your compressed air system. If you have questions, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
Visit us on the Web

## Compressed air Storage: Do you need a Receiver Tank?

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.

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

Send me an Email
Find us on the Web

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

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.

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
Visit us on the Web

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

## When to use Compressed Air Receiver Tanks (and More)

I was recently working with a process Engineer at a food packaging plant on installing a Super Air Knife to blow excess water off a food product. This product was moving single file on a conveyor belt with about 6 feet between each product. The belt was moving pretty slow so we wanted to turn the air knife on only when the product was in front of the knife, which saves compressed air and energy. To do this we used the ELECTRONIC FLOW CONTROL (EFC). If the knife ran the entire time it would be wasting any air blowing during one of the 6′ long gaps. This would also put an unnecessary strain on their already taxed compressed air system. The EFC let him only supply air to the Knife when it saw a product on the belt. To read more about the EFC click here!

This application worked perfectly, but they had one other issue. Throughout the day it seemed as if they were losing compressed air pressure at the knife. What they found was during peak compressed air usage in the plant the compressor couldn’t keep up with the demand. Fear not, the Super Air Knife was only running for 7 seconds and was off for 20 seconds. This was a perfect application for EXAIR’s Receiver Tank.

Receiver Tanks are great for applications that require an intermittent demand for a volume of compressed air. This can cause fluctuations in pressure and volume throughout the compressed air system with some points being “starved” for compressed air. EXAIR’s Model 9500-60 60 Gallon Receiver Tank can be installed near the point of high demand so there is an additional supply of compressed air available for a short duration. The time between the high volume demand occurrences should be long enough so the compressor has enough time to replenish the receiver tank.

If you have a process that is intermittent, and the times for and between blow-off, drying, or cooling allows, a Receiver Tank can be used to allow you to get the most of your available compressed air system. If you need any assistance calculating the need for a receiver, please let us help.

Note – Lee Evans wrote an easy to follow blog that details the principle and calculations of Receiver Tanks, and it is worth your time to read here.

If you would like to talk about any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer
Send me an email
Find us on the Web