Category: Compressor

How Do Membrane Dryers Work?

Published on by Russ BowmanLeave a comment

Water and water vapor can cause big problems in a compressed air system. That’s why compressed air dryers are a critical component of those systems. There are a few different types, and they all have their pros and cons. My colleague Jordan Shouse summed up the selection process pretty succinctly in a past blog: Compressed Air Dryers : What are they Good For? I particularly enjoyed his reference to Edwin Starr’s famous protest song, War (What Is It Good For?)

While they are all indeed “good for (as Jordan said) absolutely A LOT”, I wanted to take (another) deeper dive into one particular type. Membrane dryers are among the newer types of compressed air dryers. As the name suggests, they use a semi-permeable membrane whose structure allows molecules of certain fluids to pass through faster than others, thereby separating those certain fluids from the primary volume. Membrane separation technology is commonly used in:

  • Water purification and desalination (removal of particulates and salts)
  • Nitrogen separation (removal of oxygen and other trace gases)
  • Removing moisture from compressed air (removal of water vapor)

A membrane dryer is made of a cylinder containing very small polymer tubes that have a special coating inside. This coating allows the above-mentioned water & water vapor to pass through more readily than the nitrogen, oxygen, and other trace gases found in the atmospheric air that the compressor has drawn in.

As compressed air enters the cylinder, it’s directed through the polymer tubes, which allow water (but not air) to pass through their walls due to the difference in partial pressure between the gases (e.g., compressed air & water vapor) on the inside, & outside, of the tubes. Air flow, traveling in the opposite direction outside the tubes, sweeps the water out. The higher the sweep air flow rate, the lower the dew point of the compressed air out.

The advantages of membrane dryers are:

  • No moving parts to wear or break.
  • No electricity required.
  • Easy to install.
  • Unaffected by environmental contamination.
  • Compact design.

While environmental contamination isn’t a concern, they are very sensitive to internal contamination, like oil & oil vapor. Membrane dryers are commonly supplied with coalescing filters to minimize any issues there.

One disadvantage (kind of) is their limited flow capacity: the highest capacity membrane dryers are capable of passing around 200 SCFM, meaning they can only be used in small-to-mid-sized systems. I said “kind of” above because, if a certain part of the compressed air system requires a different level of dry air than the rest of the plant, membrane dryers are an inexpensive and easy way to provide that. That’s “kind of” an advantage, in that situation, actually.

Another disadvantage (kind of) is the amount of purge air they lose. Remember, membrane technology means certain fluids will pass through faster & more readily – but not exclusively – so they’re going to lose some of that brand new compressed air along with the water vapor. And the lower you want the dew point to be, the more purge air will be lost. However, the purge air loss is minimal when they’re discharging air dried to a dew point in the 40°F range, and that’s perfectly acceptable in many industrial compressed air systems.

I want to help you get the most out of your compressed air system, so when you think of compressed air, think EXAIR! If you’ve got questions, we’re here to help. Give me a call.

Russ Bowman, CCASS

Application Engineer
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Fixing Leaks and Saving Money

Published on by Al WooffittLeave a comment

Compressed air is an incredibly useful resource, that comes with many advantages over non-pneumatic alternatives. You will find compressed air being used in a variety of industries and applications. It is so widely used that it often called the 4th utility. And as with any utility, it is important to be mindful of the cost, and how to make the most of it.

One simple way to save compressed air is to find and fix leaks in your compressed air system. According to the Compressed Air and Gas Institute, leaks should not exceed 5-10% of your systems air supply (we would obviously want 0%, but realistically this is unachievable). However, it is not uncommon to see leaks account for over 30% of many facilities compressed air supply being lost through leakage.

We think leak detection, and correction, is so important, that it is step 2 of our six simple steps to optimize your compressed air system. We have written many blogs on these six steps. To put some context around it, leaks the size of 1/16″, 1/8″ and 1/4″ holes will cost the following:
 

Knowing the cost of leaks is one thing, but finding them is another challenge altogether. Many leaks are undetectable to the human ear. That’s where EXAIR’s Ultrasonic Leak Detector comes in. Our Model 9207 can detect these high-frequency sounds, allowing you to pinpoint where they are. With the two attachments included; the parabola to locate leaks up to 20 feet away, and the tube attachment to define the exact location, our simple-to-use instrument will save you money, as well as a lot of headaches.

If you would like to discuss how EXAIR’s Ultrasonic Leak Detector can save you money, don’t hesitate to give us a call!

Al Wooffitt
Application Engineer

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Intelligent Compressed Air: Air Compressor Isentropic Efficiency

Published on by Russ BowmanLeave a comment

If you’re reading the EXAIR blog, odds are you’re interested in getting the most out of your compressed air system. While using engineered compressed air products is certainly one of the best ways to do that (see our Six Steps To Optimizing Your Compressed Air System), there are some things you can look at on the supply side as well. One such metric – and a key one, at that – is isentropic efficiency.

In a nutshell, isentropic efficiency is a measure of how well an air compressor converts the electrical energy it consumes into compressed air. The basic formula is a ratio between the compressor’s actual performance to that of an ideal compression process. Mathematically, it’s expressed as:

Now, as long as air compressors have moving parts, the actual energy consumed will always be higher than the amount of energy required for an ideal process. That’s because the ideal process ignores inescapable losses due to friction between – and inertia of – moving parts, electrical losses (motor efficiency), pressure drops, and heat of compression. So, like any other machine or engine, you’ll never get 100% efficiency.

It’s still a great idea to look for the highest efficiency. So great, in fact, that the U.S. Department of Energy, just this month, began efficiency regulation for oil-flooded rotary air compressors, meaning these compressors will have to meet minimum standards of isentropic efficiency. Specific Power used to be the standard by which an air compressor’s efficiency would be evaluated. It’s the ratio of power consumption to the amount of compressed air produced, normally expressed as kW/100CFM. That doesn’t take the compressor discharge pressure into consideration, which does indeed affect the power needed to generate a given amount of compressed air. We know that a 2psi pressure change will result in a 1% change in power consumption. So, if one manufacturer reports the Specific Power as kilowatts per 100 CFM @100psig, and another reports it as kilowatts per 100 CFM @140psig, that 40psi difference means a 20% variance.

Now, that doesn’t mean we stop using Specific Power – it’s one of the two variables in the isentropic efficiency equation. The other being, of course, the discharge operating pressure:

Where:

  • 16.52 and 0.2857 are constants
  • p2 is the discharge operating pressure (psig)
  • 14.5 is atmospheric pressure (psi) – this corrects gauge pressure to absolute pressure
  • P2 is Specific Power

The Compressed Air & Gas Institute (CAGI) publishes data sheets that are analogous to the fuel efficiency stickers on new car windows. Here’s a sample of one:

And, using the isentropic efficiency formula:

We get an isentropic efficiency of 86.50% (close enough to the CAGI Data Sheet’s 86.47%; likely due to a significant figure discrepancy in the calculations), which is pretty good. The highest published isentropic efficiency is about 92%. At EXAIR, our mission is to help you get the most out of our products and your compressed air system. If you have questions, we’ve got answers – give me a call.

Russ Bowman, CCASS

Application Engineer
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EXAIR’s Cold Gun Promotion

Published on by Al Wooffitt1 Comment

It’s that time of year again for EXAIR‘s Cold Gun Promotion (online only). From November 1st 2024 through to the end of the year, you can receive a Dual Point Hose Kit for free with the purchase of our promotional Cold Gun System w/ Single Point Hose Kit or promotional High Power Cold Gun System w/ Single Point Hose Kit. These hose kits come with standard point tips or 1″ fan tips. The dual point kit gives you the ability to provide cooling to more than one side of large diameter cutters and components that need cooling.

Cold Guns Systems

So, what’s so great about EXAIR’s Cold Gun? If you’re looking for a way to extend the life of your tools by keeping them cool without the mess that can be left when using a coolant, then our Cold Gun is the perfect solution. When supplied with a source of compressed air, the Cold Gun and High Power Cold Gun produces a stream of clean, cold air that is 50°F below your compressed air supply temperature. In addition to this, the Cold Gun is very quiet at only 70dBA and has no moving parts to wear out. Just supply it with clean, dry compressed air, and it will run maintenance free for many years!

With a magnetic base, the Cold Gun is easy to install and mount. The Cold Gun is an ideal alternative to messy and expensive coolant mist systems. It eliminates the cost of purchase and disposal of cutting fluids as well as worker related health problems from breathing airborne coolant or slipping on wet floors. Replacing a coolant-based system also eliminates the need for secondary cleaning operations after milling or drilling.

If you would like to discuss how an EXAIR Cold Gun can help you with your coolant application, then give us a call!

Al Wooffitt
Application Engineer

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