Which Condensate Drain Is Best For Your Compressed Air System?

In a perfect world, your air compressor’s intake would be free of dirt, oil, and water. Proper maintenance (i.e., periodic cleaning and/or changing) of the intake filter will keep most of the dirt out. Oil and water vapor will pass right through…but that’s not the end of the world (however imperfect it may be); they’re easy to take care of later in the process.

Once these vapors have been compressed (along with all that air that was drawn in), it’ll go into the receiver (usually via an aftercooler in industrial compressors) where it cools down, and that vapor condenses. If it’s left alone, a couple of things can happen:

  • Standing water in the bottom of a steel tank will cause corrosion. This can be carried into your compressed air distribution system. Over time, it will also rust through the reservoir. You don’t want either of these things to happen.
  • Eventually, it’ll take up enough space that your reservoir’s capacity will effectively shrink. That can cause your compressor to cycle rapidly. You don’t want that either.

Even the smallest of compressors will have manual drain valves on the bottoms of their reservoirs. Users will simply blow down the gallon or so tank every so often and go about their business. The small amount of electrical power that the compressor will use to recharge those tanks makes this a perfectly acceptable practice.

In the perfect world I mentioned above, the large reservoirs on industrial air compressors could be drained of condensate in the same manner. There are a few challenges to periodic manual draining:

  • You could do it on a schedule, but varying levels of humidity mean different accumulation rates of condensation. Weekly blowdowns might be OK in the winter, but you may need to do it daily in the summer. And a couple days a week in the spring or fall. It can be a real chore to keep track of all of that.
  • A practiced operator may develop the skill to shut the valve immediately upon the last drop of condensate passing. More often than not, though, you’re going to lose some compressed air doing it manually.
  • File this under “don’t try this at home (or anywhere, really)” – an unfortunately all-too-common practice is to just leave a manual drain cracked open. It works, but it wastes compressed air. On purpose. There’s too much accidental waste to give this any further discussion. Just don’t do it.
  • Plain old forgetfulness, someone going on vacation, or even leaving the company could result in someone else noticing the compressor is frequently cycling (because the reservoir is filling with water…see above), and realizing nobody’s drained the tank in a while.

Again, these manual drains are quite common, especially in smaller air compressor systems…and so are the above challenges. I may or may not have personal experience with an incident similar to that last one. Good news is, there are automated products designed to prevent this from happening to you:

  • Timer drains are popular and inexpensive. They operate just as advertised: a programmable timer opens and closes the drain valve just like you tell it to. They don’t do anything at all to address the first two challenges above: they might blow down for longer than needed (and waste compressed air) or not long enough (and allow water to build up in the reservoir.) They come in two primary configurations:
    • Solenoid Valve: the timer energizes the valve’s coil to open the valve, and a spring shuts it when the timer runs out. Strainers will prevent blockage, and will need periodic maintenance.
    • Ball Valve: the timer operates an electric actuator to open & close the valve. The full port opening of the ball valve means a strainer is usually not necessary, so these are less maintenance intensive.
  • Demand (AKA “no waste” or “zero loss”) drains are actuated by the condensate level in the reservoir. They don’t discharge any of the reservoir’s compressed air, because they close before the last bit of water exits. There are a few common options to choose from:
    • Mechanical float drains can be internal or external…the latter is more common for use with air compressor reservoirs; the former is fairly standard with point-of-use filters (more on that later). When the liquid level rises, the float opens the drain; when liquid level drops, the float closes the drain…easy as that. They CAN be susceptible to clogging with debris, but many have screens to prevent or limit that.
    • Electronic types use a magnetic reed switch or capacitance device to sense the condensate level…so they require electric power.
    • These cost more than the timer types, though, and they’ve got a number of moving parts, so they can find themselves in need of repair. Inexpensive and user-friendly rebuild kits are oftentimes available, and many of these come with alarms to let you know when to use that rebuild kit.

Whether you have a manual, timer, or demand drain, keep in mind that some moisture can still be carried over, and rust/scale can still form in pipelines. Good engineering practice calls for point-of-use filtration, like EXAIR’s Automatic Drain Filter Separators and Oil Removal Filters. If you’d like to talk more about getting the most out of your compressed air system, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Why Dryers Are Needed in Compressed Air Systems

Air compressors are extremely proficient at compressing anything in the air they are intaking. With that air that is taken in, moisture is going to be present. The amount of moisture will all depend on where you are located geographically and the ambient conditions in the area. Here in Ohio, we experience all 4 seasons so the moisture content is higher in the air during the summer months, rather than the winter months. When this air is saturated with water vapor and the conditions are right, the air reaches a point it cannot hold any additional water vapor. This point is known as the dew point of the air and water vapor will begin to condense to form droplets.

When ambient air is compressed, heat is generated and the air increases in temperature. In most industrial compressed air systems, the air is then processed to an aftercooler, and that is where condensation begins to form. To remove the condensation, the air then goes into a separator which traps the liquid water. The air leaving the aftercooler is typically saturated at the temperature of the discharge, and any additional cooling that occurs as the air is transferred will cause more liquid to condense out of the air. To address this moisture, compressed air dryers are used.

It is critical to the quality of the system and components downstream that actions are taken to prevent this condensation in the air. Condensation is generally detrimental to any point of use application and or the piping that conveys the air. Rust and/or corrosion can occur anywhere in the piping, leading to scale and contamination of the compressed air and processes. When trying to dry products off using compressed air or using the air to atomize a liquid such as paint, adding in these contaminants and moisture will cost production losses.

There are several options when it comes to the type of dryer that one may consider installing on their compressed air supply side.

• Refrigerant Dryer – the most commonly used type, the air is cooled in an air-to-refrigerant heat exchanger.
• Regenerative-Desiccant Type – use a porous desiccant that adsorbs (adsorb means the moisture adheres to the desiccant, the desiccant does not change, and the moisture can then be driven off during a regeneration process).
• Deliquescent Type – use a hygroscopic desiccant medium that absorbs (as opposed to adsorbs) moisture. The desiccant is dissolved into the liquid that is drawn out. Desiccant is used up and needs to be replaced periodically.
• Heat of Compression Type – are regenerative desiccant dryers that use the heat generated during compression to accomplish the desiccant regeneration.
• Membrane Type– use special membranes that allow the water vapor to pass through faster than the dry air, reducing the amount of water vapor in the air stream.
The air should not be dried any more than is needed for the most stringent application, to reduce the costs associated with the drying process. A pressure dew point of 35°F to 38°F (1.7°C to 3.3°C) often is adequate for many industrial applications. Lower dew points result in higher operating costs.
If you have questions about compressed air systems and dryers or any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR, and I or any of our Application Engineers can help you determine the best solution.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

How to Manage Condensate in Your Compressed Air System

If you operate an air compressor, you’re drawing water vapor into your compressed air system.  Factors like climate control (or lack thereof,) and humidity will dictate how much.  If (or more to the point, when) it condenses, it becomes an issue that must be addressed.  There are several types of dryer systems to choose from, usually when you buy your compressor…we’ve covered those in a number of blogs.  Some of these can leave a little more water vapor than others, but remain popular and effective, when considering the cost, and cost of operation, of the different types.

So, how do you handle the condensate that the dryer doesn’t remove?

  • Receivers, or storage tanks (like EXAIR Model 9500-60, shown to the right,) are commonly used for several reasons:
    • By providing an intermediate storage of compressed air close to the point of use, fluctuations across the system won’t adversely affect an application that needs a constant flow and pressure.
    • This also can keep the air compressor from cycling rapidly, which leads to wear & tear, and additional maintenance headaches.
    • When fitted with a condensate drain (more on those in a minute,) they can serve as a wet receiver.  Condensate collects in the bottom and is manually, or automatically emptied.
  • Condensate drains, while popularly installed on receivers, are oftentimes found throughout larger systems where the vapor is prone to condense (intercoolers, aftercoolers, filters and dryers) and where the condensation can be particularly problematic (drip legs or adjacent to points of use.) There are a couple of options to choose from, each with their own pros & cons:
    • Manual drains are self explanatory: they’re ball valves; cycled periodically by operators.  Pros: cheap & simple.  Cons: easy to blow down too often or for too long, which wastes compressed air.  It’s also just as easy to blow down not often enough, or not long enough, which doesn’t solve the condensate problem.
    • Timer drains are self explanatory too: they cycle when the timer tells them to. Pros: still fairly cheap, and no attention is required.  Cons: they’re going to open periodically (per the timer setting) whether there’s condensate or not.
    • Demand, or “zero loss” drains collect condensate until their reservoir is full, then they discharge the water.  Pros: “zero loss” means just that…they only actuate when condensate is present, and they stop before any compressed air gets out.  Cons: higher purchase price, more moving parts equals potential maintenance concerns.
  • The “last line of defense” (literally) is point-of-use condensate removal.  This is done with products like EXAIR Automatic Drain Filter Separators.  They’re installed close to compressed air operated devices & products, oftentimes just upstream of the pressure regulator and/or flow controls…the particulate filter protects against debris in these devices, and the centrifugal element “spins” any last remaining moisture from the compressed air flow before it gets used.

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

Efficient and safe use of your compressed air includes maintaining the quality of your compressed air.  If you’d like to find out more about how EXAIR Corporation can help you get the most out of your compressed air system, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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