Compressor Controls – Maximize Supply Side Efficiency

Air Compressor
Air Compressor and Storage Tanks

One of the most important aspect of an efficient compressed air delivery system is effective utilization of compressor controls. The proper use of compressor controls is critical to any efficient compressor system operation. In order to reduce operating costs, compressor controls strategies need to be developed starting with minimizing the discharge pressure. This should be set as low as possible to keep energy costs to a minimum.

The compressor system is designed with maximum air demand in mind. During periods of lower demand compressor controls are used to coordinate a reduction in output that matches the demand. There are six primary types of individual compressor controls:

  1. Start/Stop – This is the most basic control. The start/stop function will turn off the motor in response to a pressure signal.
  2. Load/Unload – The motor will run continuously, but the compressor unloads when a set pressure is reached. The compressor will then reload at a specified minimum pressure setting.
  3. Modulating – Restricts the air coming into the compressor to reduce compressor output to a specified minimum. This is also known as throttling or capacity control.
  4. Dual/Auto Dual – On small reciprocating compressors, this control allows the selection of either Start/Stop or Load/Unload.
  5. Variable Displacement – Gradually reduces the compressor displacement without reducing inlet pressure.
  6. Variable Speed – Controls the compressor capacity by adjusting the speed of the electric motor.

Most compressor systems are comprised of multiple compressors delivering air to a common header. In these types of installations, more sophisticated controls are required to orchestrate the compressor operation. Network controls link together each compressor in the system to form a chain. Usually, one compressor will assume the lead role with the others taking commands from the primary compressor. Some disadvantages of network controls include: only having the ability to control the compressors, cannot be networked with remote compressor rooms without a master control, and they generally only work well with compressors of the same brand due to microprocessor compatibility issues.

In more complicated systems, master controls can be used to coordinate all of the necessary functions to optimize the compressor system. Master controls have the ability to monitor and control all of the components within the system. The high-end master control systems utilize single point control logic with rate of change dynamic analysis in order to determine how the system will respond to changes. Changes on the demand side, supply side, or the ambient environment will all impact a compressor’s performance. An effective master control will be able to identify these changes and provide the most energy efficient response.

At the point of use, it’s always important to ensure you’re using a product that was engineered to reduce compressed air consumption. EXAIR’s line of Intelligent Compressed Air Products are available from stock to help you manage your overall operating costs.

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

Images courtesy of thomasjackson1345 via Creative Commons License.

Proper Compressed Air Supply Plumbing Equals Success

EXAIR manufactures and stocks Super Air Knives in lengths ranging from 3”-108”. They’re designed to dramatically reduce compressed air usage when compared to similar blowoffs while still maximizing both force and flow. With an air entrainment ratio of 40:1, it’s the ideal solution for a variety of applications that necessitate a wide, laminar sheet of high velocity airflow.

I recently worked with a customer who makes wooden pallets. They were using a Model 110048 48” Super Air Knife to remove sawdust from the pallets prior to stacking them. When the grooves are cut into the pallet to accommodate the forks from a forklift or pallet-jack, there’s a good amount of sawdust that remains on the pallet. They would prefer to not have sawdust all over the finished pallets that they send to customers, so they looked towards a Super Air Knife to provide a curtain of air capable of removing that sawdust just prior to stacking them.

They purchased the Model 110048, but after installing it they didn’t get the level of force they had been hoping for. After some initial discussions, we identified that the issue lied with the plumbing of the air supplied to the knife. A 48” Super Air Knife will need to be fed with compressed air to (3) of the ¼ NPT air inlets. This ensures that an adequate volume of air is fed to the full length of the knife, keeping a consistent airflow.

Not only had they been plumbing compressed air to just (1) air inlet, but they were also using a restrictive quick-disconnect fitting. The I.D. of a quick connect fitting restricts the overall volume of air that can be passed through it. Length of the pipe or hose is also critical as the diameter of the pipe will need to be larger for longer runs or greater volumes. Accompanying any Super Air Knife is our Installation & Maintenance Guide which outlines the necessary requirements for each available length that we have available as well as how many air inlets need to be supplied with compressed air.

SAK pipe sizing

To confirm that air supply was the issue, they installed a pressure gauge directly at the air inlet to the knife. Line pressure was around 90 PSIG, but when they opened the valve and supplied air to the knife the pressure gauge dropped all the way to 35 PSIG. We’ve talked about pressure drop before here on the EXAIR Blog, the only way to confirm this is to take a pressure reading directly at the air inlet.

They removed the quick disconnect fitting, increased to a 1/2″ supply hose in place of 1/4″, and plumbed compressed air to each end and the center air inlet. On all Super Air Knives, compressed air inlets are available on either end as well as on the bottom. After fixing their plumbing, they noticed a dramatic increase in both force and flow and the pressure directly at the air inlet increased to 85 PSIG. The sawdust was easily blown off of the pallets and the customer was pleased that their pallets were free of sawdust.

sak pallet

At EXAIR, we stand by our products with the Unconditional 30 Day Guarantee. If you’ve just purchased a new product and aren’t seeing the results that you were hoping for give us a call. Our highly-trained team of Application Engineers is ready and standing by to investigate the application and provide support to help make sure you’re getting the most out of our products. Most of the times the solution is simple, but we won’t be satisfied until we find a resolution!

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

Understanding Compressed Air Supply Piping

An important component of your compressed air system is the supply piping. The piping will be the middle man that connects your entire facility to the compressor. Before installing pipe, it is important to consider how the compressed air will be consumed at the point of use.  You’ll also need to consider the types of fittings you’ll use, the size of the distribution piping, and whether you plan to add additional equipment in the next few years. If so, it is important that the system is designed to accommodate any potential expansion. This also helps to compensate for potential scale build-up (depending on the material of construction) that will restrict airflow through the pipe.

Air Compressor
Air Compressor and Storage Tanks

The first thing you’ll need to do is determine your air compressor’s maximum CFM and the necessary operating pressure for your point of use products. Keep in mind, operating at a lower pressure can dramatically reduce overall operating costs. Depending on a variety of factors (elevation, temperature, relative humidity) this can be different than what is listed on directly on the compressor. (For a discussion of how this impacts the capacity of your compressor, check out one of our previous blogs – Intelligent Compressed Air: SCFM, ACFM, ICFM, CFM – What do these terms mean?)

Once you’ve determined your compressor’s maximum CFM, draw a schematic of the necessary piping and list out the length of each straight pipe run. Determine the total length of pipe needed for the system. Using a graph or chart, such as this one from Engineering Toolbox. Locate your compressor’s capacity on the y-axis and the required operating pressure along the x-axis. The point at which these values meet will be the recommended MINIMUM pipe size. If you plan on future expansion, now is a good time to move up to the next pipe size to avoid any potential headache.

After determining the appropriate pipe size, you’ll need to consider how everything will begin to fit together. According to the Best Practices for Compressed Air Systems from the Compressed Air Challenge, the air should enter the compressed air header at a 45° angle, in the direction of flow and always through wide-radius elbows. A sharp angle anywhere in the piping system will result in an unnecessary pressure drop. When the air must make a sharp turn, it is forced to slow down. This causes turbulence within the pipe as the air slams into the insides of the pipe and wastes energy. A 90° bend can cause as much as 3-5 psi of pressure loss. Replacing 90° bends with 45° bends instead eliminates unnecessary pressure loss across the system.

Pressure drop through the pipe is caused by the friction of the air mass making contact with the inside walls of the pipe. This is a function of the volume of flow through the pipe. Larger diameter pipes will result in a lower pressure drop, and vice versa for smaller diameter pipes. The chart below from the Compressed Air and Gas Institute Handbook provides the pressure drop that can be expected at varying CFM for 2”, 3”, and 4” ID pipe.

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Air Pressure Drop

To discuss your application and how an EXAIR Intelligent Compressed Air Product can help your process, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer
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Twitter: @EXAIR_JS

 

Images Courtesy of  the Compressed Air Challenge and thomasjackson1345 Creative Commons.

About Rotary Scroll Compressors

The Rotary Scroll compressor is a popular style compressor and is used primarily for air conditioning refrigerant systems.  Recently, since it is very efficient, quiet and reliable it has been adopted by industrial air compressor manufacturer’s to expand their product offering for their smaller, high-efficiency product line.

They operate on the principle of two intermeshing spirals or scrolls with one being stationary while the other rotates or orbits in relation to it.  They are mounted with 180° phase displacement between them which forms air pockets having different volumes.  Air enters through the inlet port located in the rotating/orbiting scroll which fills the chambers and as is moved along and compressed along the scroll surfaces.

scroll compressor finalSome of the key advantages of a Rotary Scroll Compressor are:

  • Pulsation free delivery due to the continuous flow from the suction port to the outlet port.
  • No metal to metal contact thereby eliminating the need for lubrication
  • Low noise levels
  • Fewer moving parts means less maintenance
  • Energy Efficient
  • Air cooled

The largest disadvantage is they are available in a limited range of sizes and the largest SCFM outputs are around 100 SCFM.

This is exactly where EXAIR shines, we offer 15 product lines of highly efficient & quiet point of use compressed air products and accessories to compliment their limited output volume of air.  All EXAIR products are designed to use compressed air efficiently and quietly, many of which reduce the demand on your air compressor which will help control utility costs and possibly delay the need to add additional compressed air capacity.

As an example, EXAIR’s Super Air Knives deliver exceptional efficiency by entraining ambient air at ratios of up to 40:1 and they are able to deliver an even laminar flow of air ranging from a gentle breeze to exceptionally hard-hitting force.

Super Air Knife
EXAIR’s Super Air Knife entrains ambient air at a 40:1 ratio!

EXAIR’s Super Air Amplifiers are able to entrain ambient air at ratio’s up to 25:1.  The model 120024 – 4″ Super Air Amplifier developes output volumes up to 2,190 SCFM while consuming only 29.2 SCFM of compressed air @ 80 PSI which can easily be operated on a 100 SCFM output compressor.

Super Air Amplifier
EXAIR Air Amplifiers use a small amount of compressed air to create a tremendous amount of air flow.

For your blow off needs EXAIR’s Super Air Nozzle lineup has an offering that will fit nearly any need or application you may have.  Nozzles are available in sizes from M4 x 0.5 to  1 1/4 NPT and forces that range from 2 ounces of force up to 23 Lbs at 12″ from the discharge.  We offer sixty two nozzles that could all be operated easily from the limited discharge or a rotary scroll compressor.

nozzlescascadeosha
Family of Nozzles

If you need to reduce your compressed air consumption or you are looking for expert advice on safe, quiet and efficient point of use compressed air products give us a call.  We would enjoy hearing from you!

Steve Harrison
Application Engineer
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Wet Receivers and Condensate Drains

Receiver Tank

For properly designed compressed air systems, air compressors will use primary storage tanks, or receivers.  They are necessary to accommodate for fluctuations in airflow demand and to help prevent rapid cycling of the air compressor.  (Reference: Advanced Management of Compressed Air – Storage and Capacitance)  There are two types of primary receivers, a wet receiver tank and a dry receiver tank.  The wet receiver is located between the air compressor and the compressed air dryer where humid air and water will be stored.  The dry receiver is located after the compressed air dryer.  In this blog, I will be reviewing the wet receivers and their requirements as a storage tank.

Air compressors discharge hot humid air created by the internal compression.  A byproduct of this compression is water.  By placing a wet receiver on the discharge side of the air compressor, this will create a low velocity area to allow the excess water to fall out.  It will also give the hot air time to cool, allowing the compressed air dryers to be more effective.  With wet receivers, it will reduce cycle rates of your air compressors for less wear and store compressed air to accommodate for flow fluctuations in your pneumatic system.

But, there are some disadvantages with a wet receiver.  For compressed air dryers, it is possible to exceed the specified flow ratings.   If the demand side draws a large volume of air from the supply side, the efficiency of the compressed air dryers will be sacrificed, allowing moisture to go downstream.  Another issue with the wet receiver is the amount of water that the air compressor is pumping into it. As an example, a 60 HP air compressor can produce as much as 17 gallons of water per day.  As you can see, it would not take long to fill a wet receiver.  So, a condensate drain is required to get rid of the excess water.

Condensate drains come in different types and styles.  They are connected to a port at the bottom of the wet receiver where the water will collect.  I will cover the most common condensate drains and explain the pros and cons of each one.

  • Manual Drain – A ball valve or twist drain are the least efficient and the least expensive of all the condensate drains. The idea of having personnel draining the receiver tanks periodically is not the most reliable.  In some cases, people will “crack” the valve open to continuously drain the tank.  This is very inefficient and costly as compressed air is being wasted.
  • Timer Drain Valves – These valves have an electric timer on a solenoid to open and close a two-way valve or a ball valve. The issue comes in trying to set the correct time for the open and close intervals.  During seasonal changes, the amount of water going into the wet receiver will change.  If the timer is not set frequent enough, water can build up inside the receiver.  If too frequent, then compressed air is wasted.  Compared to the manual valve, they are more reliable and efficient; but there is still potential for compressed air waste.

    Timer Relay
  • No-waste Drains – Just like the name, these drains are the most efficient. They are designed with a float inside to open and close a drain vent.  What is unique about the float mechanism is that the drain vent is always under water.  So, when the no-waste drain is operating, no compressed air is being lost or wasted; only water is being drained.  The most common problem comes with rust, sludge, and debris that can plug the drain vent.

All wet receivers require a condensate drain to remove liquid water.  But, the importance for removing water without wasting compressed air is significant for saving money and compressed air.  EXAIR also has a line of Intelligent Compressed Air® products that can reduce your compressed air waste and save you money.  You can contact an Application Engineer for more details.

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

 

Photo: Timer Relay by connectors distribution box.  Attribution – CC BY-SA 2.0

Designing a Compressed Air Distribution System

Compressed air is used to operate pneumatic systems in a facility, and it can be segregated into three sections; the supply side, the demand side, and the distribution system.  The supply side is the air compressor, after-cooler, dryer, and receiver tank that produce and treat the compressed air.  They are generally located in a compressor room somewhere in the corner of the plant.  The demand side are the collection of end-use devices that will use the compressed air to do “work”.  These pneumatic components are generally scattered throughout the facility.  To connect the supply side to the demand side, a compressed air distribution system is required.  Distribution systems are pipes which carry the compressed air from the compressor to the pneumatic devices.  For a sound compressed air system, the three sections have to work together to make an effective and efficient system.

An analogy, I like to compare to the compressed air system, is an electrical system.  The air compressor will be considered the voltage source, and the pneumatic devices will be marked as light bulbs.  To connect the light bulbs to the voltage source, electrical wires are needed.  The distribution system will represent the electrical wires.  If the wire gauge is too small to supply the light bulbs, the wire will heat up and the voltage will drop.  This heat is given off as wasted energy, and the light bulbs will dim.

The same thing happens within a compressed air system.  If the piping size is too small, a pressure drop will occur.  This is also wasted energy.   In both types of systems, wasted energy is wasted money.  One of the largest systematic problems with compressed air systems is pressure drop.  If too large of a pressure loss occurs, the pneumatic equipment will not have enough power to operate effectively.  As shown in the illustration below, you can see how the pressure decreases from the supply side to the demand side.  With a properly designed distribution system, energy can be saved, and in reference to my analogy, it will keep the lights on.

Source: Compressed Air Challenge Organization

To optimize the compressed air system, we need to reduce the amount of wasted energy; pressure drop.   Pressure drop is based on restrictions, obstructions, and piping surface.  If we evaluate each one, a properly designed distribution system can limit the unnecessary problems that can rob the “power” from your pneumatic equipment.

  1. Restriction: This is the most common type of pressure drop. The air flow is forced into small areas, causing high velocities.  The high velocity creates turbulent flow which increases the losses in air pressure.  Flow within the pipe is directly related to the velocity times the square of the diameter.  So, if you cut the I.D. of the pipe by one-half, the flow rating will be reduced to 25% of the original rating; or the velocity will increase by four times.  Restriction can come in different forms like small diameter pipes or tubing; restrictive fittings like quick disconnects and needle valves, and undersized filters and regulators.
  2. Obstruction: This is generally caused by the type of fittings that are used.  To help reduce additional pressure drops use sweeping elbows and 45-degree fittings instead of 90 deg. elbows.  Another option is to use full flow ball valves and butterfly valves instead of seated valves and needle valves.  If a blocking valve or cap is used for future expansion, try and extend the pipe an additional 10 times the diameter of the pipe to help remove any turbulence caused from air flow disruptions.  Removing sharp turns and abrupt stops will keep the velocity in a more laminar state.
  3. Roughness: With long runs of pipe, the piping surface can affect the compressed air stream. As an example, carbon steel piping has a relative rough texture.  But, over time, the surface will start to rust creating even a rougher surface.  This roughness will restrain the flow, creating the pressure to drop.  Aluminum and stainless steel tubing have much smoother surfaces and are not as susceptible to pressure drops caused by roughness or corrosion.

As a rule, air velocities will determine the correct pipe size.  It is beneficial to oversize the pipe to accommodate for any expansions in the future.  For header pipes, the velocities should not be more than 20 feet/min (6 meter/min).  For the distribution lines, the velocities should not exceed 30 feet/min (9 meter/min).  In following these simple rules, the distribution system can effectively supply the necessary compressed air from the supply side to the demand side.

To have a properly designed distribution system, the pressure drop should be less than 10% from the reservoir tank to the point-of-use.  By following the tips above, you can reach that goal and have the supply side, demand side, and distribution system working at peak efficiency.  If you would like to reduce waste even more, EXAIR offers a variety of efficient, safe, and effective compressed air products to fit within the demand side.  This would be the pneumatic equivalent of changing those light bulbs at the point-of-use into LEDs.

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

 

Photo: Light Bulb by qimonoCreative Commons CC0