Compressed Air Membrane Dryers: What are They? How do They Work?

A critical component on the supply side of your compressor system is the dryer. Atmospheric air contained within a compressed air system contains water vapor. The higher the temperature of the air, the more volume of moisture that air is capable of holding. As air is cooled, this water vapor can no longer be contained and this water falls out in the form of condensation. The temperature where this water will drop out is referred to as the dew point.

At a temperature of 75°F and 75% relative humidity, approximately 20 gallons of water will enter a 25HP compressor during a 24-hour period. As air is compressed, this water becomes concentrated. Since it’s heated during the compression process, this water stays in a vapor form. When this air cools further downstream, this vapor condenses into droplet form.

Moisture within the compressed air system can result in rust forming on the inside of the distribution piping, process failure due to clogged frozen lines in colder weather, false readings from instruments and controls, as well as issues with the point of use products installed within the system.

The solution to this problem is to install a dryer system. We’ve spent some time here on the EXAIR blog reviewing refrigerant dryers , desiccant dryersdeliquescent dryers, and heat of compression dryers. For the purposes of this blog, I’m going to focus on one of the newer styles on the market today: the membrane dryer.

Membrane Dryer

In a membrane dryer, compressed air is forced through a specially designed membrane that permits water vapor to pass through faster than the air. The water vapor is then purged along with a small amount of air while the rest of the compressed air passes through downstream. Generally, the dew point after the membrane dryer is reduced to about 40°F with even lower dew points also possible down to as low as -40°F!

With such low dew points possible, it makes a membrane dryer an optimal choice in outdoor applications that are susceptible to frost in colder climates. Membrane dryers also are able to be used in medical and dental applications where consistent reliability is critical.

A membrane dryer does not require a source of electricity in order to operate. The compact size makes it simple to install without requiring a lot of downtime and floor space. Since they have no moving parts, maintenance needed is minimal. Most often, this maintenance takes the form of checking/replacing filter elements just upstream of the membrane dryer. The membrane itself does need to be periodically replaced, an indicator on the membrane dryer will display when it needs to be changed. If particular instruments or processes in your facility are sensitive to moisture, a membrane dryer might be the best option.

However, there are some drawbacks to these types of dryers. They’re limited to low capacity installations, with models ranging from less than 1 SCFM up to 200 SCFM. This makes them more applicable for point-of-use installations than for an entire compressed air system. The nature in which the membrane dryer works necessitates some of the air to be purged out of the system along with the moisture. To achieve dew points as low as -40°F, this can equate to as much as 20% of the total airflow. When proper filtration isn’t installed upstream, oils and lubricants can ruin the dryer membrane and require premature replacement.

Make sure and ask plenty of questions of your compressor supplier during installation and maintenance of your system so you’re aware of the options out there. You’ll of course want to make sure that you’re using this air efficiently. For that, EXAIR’s wide range of engineered Intelligent Compressed Air Products fit the bill. With a variety of products available for same-day shipment from stock, we’ve got you covered.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

Why Use Oil Removal Filters For Compressed Air

If you’re even an occasional visitor to the EXAIR Blog, you’ll know we like to write about compressed air filtration.  One reason is that many of our products have relatively small passages that can become fouled with dirt from the compressed air supply, and performance will suffer.   Even if you find yourself in that situation, though, the good news is, it’s easy to clean many of those products…worst case, some disassembly is required, but we’re here to help with that if needed.

The more pressing reason for many users is, whatever’s in your compressed air is going to get on whatever it’s coming in contact with.  That means if you’re blowing dirt or water off a part with a Safety Air Gun, you could be blowing dirt, or water ONTO it if you’re not using proper filtration.  Clean, moisture free air is a MUST for a lot of Line Vac Air Operated Conveyor applications where exclusion of contamination (food and pharma, we’re looking at you) is critical.  It’s also quite important to Cabinet Cooler System applications – dust, water, and electronics DON’T mix.

That’s why all EXAIR Intelligent Compressed Air Product Kits include a Filter Separator with a particulate element to remove solids, and a centrifugal element that spins out any moisture in the air flow supplying the product.  Sometimes, though, another  contaminant may be present, and may need to be addressed: oil.

Oil is often introduced into a compressed air system on purpose, via a lubricator installed in the supply line to pneumatic tools, to keep their moving parts, well…moving.  This is generally not a problem, as long as the lubricator’s downstream line only leads to said tools.  The most common method for UNWANTED oil to enter is from the compressor.  This happens when internal parts start to wear (like the piston rings of a reciprocating compressor,) allowing oil from the gearbox into the air side.

Just as water & dirt in your air will get on whatever you’re blowing onto, so will oil.  That’s where our Oil Removal Filters come in.  The coalescing element removes any trace of oil from the air flow, and also provides additional particulate filtration to 0.03 microns.

When properly installed downstream of an Automatic Drain Filter Separator (left,) an Oil Removal Filter (center) will provide clean, oil free air to the Pressure Regulator (right) and all downstream components.

If you want to get the most out of your compressed air system and the devices it operates, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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Preventative Maintenance for EXAIR Filters

Good engineering practice calls for point of use filtration and moisture removal, such as that provided by EXAIR Filter Separators.

I read a white paper from Parker Hannifin about compressed air filters.  The idea behind the paper was to remember your filter replacements.  Compressed air can be dirty with water, oil, pipe scale, etc.  As the filters capture the contamination, it will start to build pressure drop.  Remember, pressure drop is a waste of energy in your compressed air system.

Majority of EXAIR products use compressed air for cleaning, cooling, conveying, static elimination, coating and more.  To help keep them running efficiently, it is important to supply them with clean, dry, pressurized air.  EXAIR offers a line of Filter Separators and Oil Removal Filters to supply quality air to your equipment.  In this blog, I will explain the two types of filters that we carry and the maintenance requirements.  Filters and preventative measures can play an important part in your compressed air system.

Filter Separators are used to remove bulk liquid and contamination from the compressed air stream.  They utilize a 5-micron filter with a mechanical separation to help remove large amounts of dirt and water.  This type of filter would be considered the minimum requirement for filtration.  Most of the Filter Separators come with an auto-drain to automatically dispense the collection of oil and water.  EXAIR offers a variety of port sizes and flow ranges to meet your pneumatic flow requirement.  For maintenance, the filter elements should be changed once a year or when the pressure drop reaches 10 PSID (0.7 bar), whichever comes first.  I created a list in Table 1 below showing the correct replacement element kits for each model number.  And for any reason, if the bowl or internal components get damaged, we also have Rebuild Kits as well.  Just remember, the air quality is very important for longevity and functionality of your pneumatic systems and even for EXAIR products.

The Oil Removal Filters can make your compressed air even cleaner.  They work great at removing very small particles of dirt and oil.  They are made from glass fibers and can remove particles down to 0.03 micron.  They are designed to collect small particles and to coalesce the liquid particles into a large droplet for gravity to remove.  Because of the fine matrix, Oil Removal Filters are not great for bulk separation.  If you have a system with lots of oil and water, I would recommend to use the Filter Separator upstream of the Oil Removal Filter.  As with the Filter Separator, the filter element should be changed once a year or at a pressure drop of 10 PSID (0.7 bar).  EXAIR also offers a variety of port sizes and flow ranges.  Table 1 below shows the replacement Element Kits as well as the Rebuild Kits.  If the application requires very clean compressed air, the Oil Removal Filter should be used.

Table 1

By using EXAIR filters, they will clean your compressed air to prevent contamination on parts, performance issues, and premature failures.  As an ounce of prevention, you should add the replacement elements in stock and enter them in your preventative maintenance program.  With quality air, your pneumatic system and EXAIR products will provide you with effective, long-lasting performance without any maintenance downtime.  If you would like to discuss the correct type of filters to use in your application, you can speak with an Application Engineer.  We will be happy to help you.

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

Video Blog: Importance of Point-of-Use Filtration

When operating any of your Intelligent Compressed Air Products, something that often gets overlooked is the importance of delivering clean, dry air to those point-of-use products. Many of our products have very tight orifices to help reduce the volume of compressed air they consume. In addition, most have no moving parts to wear out and require no maintenance. That is, unless you’re using unfiltered compressed air.

Rust and scale are commonly found within the distribution system inside your facility. Old iron pipe and receiver tanks are the common culprits. A common misconception is that the air is already filtered as it exits the compressor. While this may be true, there’s still places in the distribution system that can cause issues downstream.

To eliminate the hassle of taking things apart to periodically clean, EXAIR recommends installing a point-of-use filter for all of our Intelligent Compressed Air Products. Kits are available for purchase that come with a properly sized filter to ensure your air is sufficiently clean. To see how quickly debris can clog your products, check out my video below demonstrating the difference between dirty and clean air with a Model 110006 6″ Super Air Knife.

If you’ve already purchased and installed products without filters, it’s never to late to go back and install one. Contact an EXAIR Application Engineer today and we’ll be happy to help you determine the proper size for the volume of air you’re products need.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD