In the last ten years, the design of pneumatic systems has changed dramatically, mainly due to developments in the technologies that create them. Pneumatic manufacturers’ online tools for sizing components have evolved, the fieldbus systems are ever-changing, component designs are constantly improving, and network devices such as the Industrial Internet of Things (IIoT) have reshaped the industry. All these advances play a large role in optimizing the efficiency of pneumatic systems, but the age-old practice of routine maintenance must not be overlooked. This article will focus on proper air compressor sizing, proper pneumatic component sizing and predictable preventative maintenance.
The heart of any compressed air system is the air compressor itself and the related components such as the receiver tank, aftercooler and dryer. A qualified air compressor vendor should be consulted for the specific type of components required based on environment, duty cycle, pressure and required cubic feet per minute (cfm) and safety factors for future expansion. Each of these factors will be considered when a system analysis is performed. If a particular machine function requires a higher pressure than the rest of the required function, a storage receiver tank and air amplifier can be an efficient way to provide the added pressure to that leg of the system versus increasing the pressure of the air compressor.
Proper component design and sizing is very important in order for the system to perform as intended and as efficiently as possible. To that end, never have there been more tools available for the sizing of components due largely to many manufacturers’ online sizing tools that allow for maximum system efficiency. In terms of optimizing overall system efficiency the most common components of yesterday are true today. Regulators, Pressure and Flow Controls, Filtration and properly-installed piping systems can each offer major efficiency and extended life benefits.
Industrial Regulators are typically found in two construction types, the first being sandwich style. In this design, the regulator is positioned between the subbase or manifold and the valve body. This layout is convenient but not the most efficient because the body size is mandated by the width of the valve. This can reduce the overall flow from that valve section by as much as 50 percent, requiring the valve be oversized in order to get the desired flow needed to satisfy the work to be done. A more efficient regulator would be the inline style, which has a reverse flow check that allows it to be placed between the valve and actuator for dual pressure function. Dual pressure is a simple but overlooked method to increase efficiency since many actuator cycles only have one power stroke (load in one direction). By adding a regulator to the non-power stroke, pressure can be reduced to meet that need, therefore saving energy and improving performance.
Electro-Pneumatic Pressure Control
Electro-Pneumatic Pressure Controls are offered in different design types and can be integrated into the machine logic to change pressure based on a voltage or current command signal. This type of regulator can be placed near an actuator in hard to get to locations and still provide efficient operation. Designers can also build a “pressure recipe” if known pressure adjustments are required, or interface with a machine controller. These applications can vary greatly and include some of the options listed below:
- Press Rolls (which can require different forces depending on the product/application)
- Spot Welders (these also require different forces depending on the metal gage)
- Solder Paste Dispensing
- Medical Dispensing
- Robotic Paint Spraying
- Cylinder Speed Control
- RPM Motor/Turbine Control (extremely precise speed control can be realized when adding a speed sensor as a feedback)
- Dancer Rolls (such as paper or fabric)
- Counter Balance Control
- Brake Force Control
Electro-Pneumatic Pressure Control
Flow Controls limit the actuator speed, conserving the flow generated by the compressor. The two common styles used are inline and right angle. Both are available in “Meter In” or “Meter Out”, the latter being the better option due to the compressibility of air. The right-angle style is designed to pipe directly into the actuator port where the best results can be obtained. Additionally, there is a safety element to flow controls being installed at the actuator that, should a hose or tube be severed, makes the actuator move at the desired speed versus a non-controlled, run-away effect that could possibly cause equipment damage or bodily injury.
Filtration extends the life of system components, and industrial components range in micron size from 5μm to 40μm for standard valves and actuators. The degree of the filtration required in a system is published by the component manufacturer. Some more critical applications such as instrumentation, pharmaceutical, food & beverage and air logic may require .001μm, meaning a pre-filter and coalescing filter are necessary.
Selecting the correct filtration for a particular leg of a pneumatic system is just as important as selecting the correct valving and actuators. In addition, the contamination indicator used on filters should be considered carefully in order to meet the degree of system importance. Filter indicators include a simple low-cost pressure gauge, red/green visual indicator gauge, electric indicators and pressure switches. Knowing when to replace a filter element is important because changing too soon would not be taking full advantage of the element life and can be costly, especially in terms of the coalescing element. Alternatively, waiting too long can have an adverse effect on system function.
The visual-type indicators require an effort to view them and the “out of sight, out of mind” rule may come into play. However, the electric and pressure switch-type indicators will be harder to ignore since they can provide any number of indication alarms.
Preventative Maintenance Components
Preventative Maintenance Components, such as a smart pneumatic module (SPM), take the next step in optimizing the complete pneumatic system. It keeps it at a peak performance level and significantly reduces costly down time by utilizing the IIoT to monitor system performance. The SPM can alert the appropriate personnel that a particular component is approaching the end of its life expectancy-- something that can be accomplished without taking up valuable machine controller memory.
Properly-Designed Piping Systems
Properly-Designed Piping Systems can also provide efficiency by reducing the number of sharp angles. The turbulence of one 90-degree bend can cause a pressure drop of 3-5 PSI. Another factor to consider is moisture. Moisture is a by-product of a compressed air system and causes rust in some types of piping. The rust that forms in piping systems can cause contamination and premature failure in components. In addition, the rust scale that forms on the inside of a pipe can cause additional air flow turbulence, which is a direct reflection of pressure drop. Using aluminum piping will avoid the rust issue. Drip leg drains can also offer a way to rid water at specific points in the piping system. Drop legs off of header pipes should be taken off the top rather than the bottom where moisture can accumulate.
Understanding the overall system of potential energy, control of that energy, proper maintenance of the system including removal of water, moisture and impurities and designing the pneumatic control circuits for optimum efficiency is always the ultimate goal. After considering all the factors above, trying to lay out current and future objectives of the system is the key element in reaching that goal.
About the Author
Bill Nevills is a Certified Fluid Power Specialist at Valin Corporation, a leading technical solutions provider for the technology, energy, life sciences, natural resources and transportation industries. Valin offers personalized order management, on-site field support, comprehensive training and applied expert engineering services utilizing automation, fluid management, precision measurement, process heating, filtration and fluid power products. Valin also has solutions for managing the compressed air system mentioned in this article. For more information, please visit www.valin.com.
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