Intelligent Compressed Air: Rotary Air Compressors

Air Compressor
Air Compressor and Storage Tanks

One thing that is found in virtually every industrial environment is an air compressor. Some uses for the compressed air generated are: powering pneumatic tools, packaging, automation equipment, conveyors, control systems, and various others. Pneumatic tools are favored because they tend to be smaller and more lightweight than electric tools, offer infinitely variable speed and torque, and can be safer than the hazards associated with electrical devices. In order to power these devices, compressed air must be generated.

There are two main categories of air compressors: positive-displacement and dynamic. In a positive-displacement type, a given quantity of air is trapped in a compression chamber. The volume of which it occupies is mechanically reduced (squished), causing a corresponding rise in pressure. In a dynamic compressor, velocity energy is imparted to continuously flowing air by a means of impellers rotating at a very high speed. The velocity energy is then converted into pressure energy. We’ve discussed the different styles of air compressors here on the EXAIR Blog in the past. Today I’d like to highlight the rotary compressors, one of the positive-displacement types of compressors.

Positive-displacement compressors are broken into two categories: reciprocating and rotary. The rotary compressors are available in lubricant-injected or lubricant-free varieties. Both styles utilize two inter-meshing rotors that have an inlet port at one end and a discharge port at the other. Air flows through the inlet port and is trapped between the lobes and the stator. As the rotation continues, the point inter-meshing begins to move along the length of the rotors. This reduces the space that is occupied by the air, resulting in an increase in pressure.

In the lubricant-injected varieties, the compression chamber is lubricated between the inter-meshing rotors and bearings. This lubricant protects the inter-meshing rotors and associated bearings. It eliminates most of the heat caused by compression and acts as a seal between the meshing rotors and between the rotor and stator. Some advantages of the lubricant-injected rotary compressor include a compact size, relatively low initial cost, vibration free operation, and simple routine maintenance (replacing lubricant and filter changes). Some drawbacks to this style of compressor include lower efficiency when compared with water-cooled reciprocating compressors, lubricant carry over must be removed from the air supply with a coalescing filter, and varying efficiency depending on the control mode used.

In the lubricant-free varieties, the inter-meshing rotors have very tight tolerances and are not allowed to touch. Since there is no fluid to remove the heat of compression, they typically have two stages of compression with an inter-cooler between and an after cooler after the second stage. Lubricant-free compressors are beneficial as they supply clean, oil-free compressed air. They are, however, more expensive and less efficient to operate than the lubricant-injected variety.

Each of these compressors can deliver air to your Intelligent Compressed Air Products. If you’re looking to reduce your compressed air consumption and increase the safety of your processes contact an EXAIR Application Engineer today. We’ll be happy to discuss the options with you and make sure you’re getting the most out of your compressed air usage.

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

EXAIR Digital Flowmeters With Wireless Capability

“You can’t manage what you don’t measure” is a well-known axiom in engineering & process improvement circles.  We talk to callers every day who are keen on conserving compressed air use in their facilities by making a few tweaks, considering a complete overhaul, or more often, some point in between.  Bottom line (literally) is, compressed air isn’t cheap, so small gains in efficiency can add up.  And large gains can be complete game-changers…following our Six Steps To Optimizing Your Compressed Air System has resulted in users being able to shut down 50 and 100 HP air compressors, saving thousands of dollar A MONTH in operating costs.

Step #1 is measurement, and that’s where the EXAIR Digital Flowmeter comes in.  They’re easy to install, highly accurate, extremely reliable, and available for just about any size pipe used for compressed air distribution.  They can output a 4-20mA signal straight from their PCB board, or serial comms (RS485) through an optional control board.  USB Data Loggers and Summing Remote Displays have proven to be value-added accessories for data management as well.

Summing Remote Display (left) for remote indication and totalizing data. USB Data Logger takes data from the Digital Flowmeter to your computer and outputs to its own software (shown above) or Microsoft Excel.

If you want to go wireless, we can do that too: using ZigBee mesh network protocol, a radio module is installed in the Digital Flowmeter with wireless gateway to transmit data to an Ethernet connected gateway.  The transmitting range is 100 ft (30 meters,) and the data can be passed from one radio module to another, allowing for multiple Digital Flowmeter installations to extend the distance over which they can communicate with the computer you’re using for central monitoring.  Advantages include:

  • Wireless monitoring of EXAIR Digital Flowmeters throughout your plant.
  • Prevents unwanted joining upon the network.
  • Monitoring software is included at no extra charge.
  • Measures & transmits both current air usage, and cumulative air usage data.
  • 128 bit encryption for wireless transmissions.
  • Comes configured & programmed, out of the box, available for installation on 1/2″ to 4″ SCH40 iron pipe, or 3/4″ to 4″ Type L copper pipe.
Digital Flowmeter w/ Wireless Capability, Gateway, and Drill Guide Kit

If you’d like to find out more about how easy it is to measure, manage, and optimize your compressed air usage, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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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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Intelligent Compressed Air: Membrane Dryers

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 dryers, deliquescent 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

 

Membrane Dryer Schematic – From Compressed Air Challenge, Best Practices for Compressed Air Systems, Second Edition