Four Ways to Boost the Efficiency of Pneumatic Systems

Throughout most of industrial history, nearly every plant had an air system, which was fed by central compressors that operated whether production was being done or not. However, modern facilities managers are realizing that air is not free, and as such the modern pneumatic system has come under scrutiny for increases in efficiency.

Energy consumption is one of the key factors determining how a machine or system is received these days. Different regions of the world have experienced differing energy costs over time. But today, users in every region want to squeeze the most bang from the fewest pneumatic bucks. Fortunately, most major vendors of pneumatics are prepared to help you work toward this goal. Trade organizations like the USA’s National Fluid Power Assoc. (NFPA) have useful guidelines to assist in designing efficient pneumatics. International standards help ensure that compliant components, wherever built, will deliver good performance and value. And Total Cost of Ownership (TCO) guidelines, to be covered in a future Design World article, will help you choose the right type of system for your job.

Still, there are several simple steps that can be taken to increase the efficiency of a pneumatic system with speed and ease. They are given as follows:


1: Beware of oversizing components

For decades, oversizing actuators was common practice. If an application needed a certain size cylinder, the next larger size was usually installed instead.  This is because, at the same pressure, the larger actuator will bring more force to bear on the task; the philosophy was that the larger actuator could better deal with heavier or misaligned loads.

However, oversizing an actuator is simply wasting money. Over a machine's useful service life, an oversized actuator can add up to a significant amount of money. Optimally-sized actuators can reduce air consumption by 15% or more compared to commonly oversized actuators. However, optimal sizing need not be an complicated affair: many vendors simplify the process with online optimization programs that require only a few clicks and some very basic inputs from the user. Some of these calculators even allow the user to compare the energy costs of their current system with an optimized one, to better determine the total cost of switching components.


2: Reduce volume by cutting distance between valves and actuators

Air pressure is a function of volume and pressure, and thus controlling both leads to direct controls in energy costs. Efficiency can be increased by reducing the lengths of tubing between components. These tubing runs are essentially dead volume, and increase an operation's pressure losses. For best results, users should seriously examine the advantages of a decentralized air supply, which require long lines, cumbersome valves, and will usually consume a great deal of energy. Point-of-use systems can further cut energy use by 35% while yielding faster response times and higher cycle frequencies. These decentralized systems are also available in engineered polymers - perfect for washdown and food applications.


3: Avoid using excess pressure

Pneumatic systems frequently waste energy by supplying higher pressure than an actuator needs. For instance, in many applications cylinders either push or pull a load, but not both. Yet most often machines use the same pressure for both extend and retract strokes, which is extremely inefficient.

Using pressure regulators to supply the right pressure for each task can lower energy consumption by more than 25%. For instance, “smart” regulators combine digital control electronics with proportional valves. They constantly compare preset pressure limits with actual values to ensure exact metering.

Rexroth’s term for this is energy on demand, based on decentralized intelligence to adapt the pressure individually to needs and thus raising energy efficiency. The pressure profile of an actuator’s movement is divided into different phases: Start, movement, end and return stroke. Start and end phases usually require high energy, while movement and return stroke phases can be performed with a significantly lower pressure. Even if the reduced pressure usage distance appears short, it is sufficient enough to optimize the motion and to minimize hard end position stops. When many thousand repetitions of the movement are performed, the incremental savings accumulate to a noticeable efficiency increase of the entire process.

One concern to guard against: operators commonly increase supply pressure on regulators in hopes of improving performance, but this wastes significant amounts of money in air and operating costs for no actual benefit - if components are sized correctly. It is important to monitor and ensure machine pressure remains within designated limits to avoid wasting energy.


4: Minimize leakage

Every pneumatic system can save energy by avoiding leaks. Statistics from the Dept. of Energy suggest the problem is widespread: the average facility, estimates show, has 30 to 35% leakage if it hasn’t taken recent action. Valves and deteriorated seals are two common sources. Some valve designs, such as lapped-spool valves with metal seals, have inherent internal leakage that is constant as long as air is supplied to the valve. Switching to comparable valves with soft seals can significantly reduce leakage.

Another source of leaks is deterioration of seals. If standard seals are observed to degrade, consider extreme-service seals like Viton, Teflon, or polyurethane.

Modern air-preparation units are available with an integrated air-volume sensor. The sensor emits an electrical pulse each time a specific volume of compressed air has passed through the air-preparation package. The electrical pulse signals can be totaled by the controller and therefore actual air consumption (and energy costs) can be calculated for the machine over a period of time. This also lets users detect increases in machine air consumption that indicate developing leaks or nonscheduled changes to the operating pressures for the motions of the machine. The real life cost of leakage and overpressurization can be counted as well as the cost savings from correcting these problems.

According to National Resources Canada, small leakages in compressed air systems can add up to significant costs. For example, a single leak as small as 1/16 in. on a compressed air system running 24/7 at 125 PSI can cost over $1000/yr. That’s for a single leak.

Multiply those numbers by several leaks and you’re talking serious money, notes a Festo quality engineer. “When you go into a plant and hear the leaks,” he says. “That’s just money being burned up.”

Festo offers customer services including leak detection, air quality and similar air auditing services. The company also offers a new system for monitoring and diagnosing sources of air consumption in pneumatic systems. It includes pressure and flow sensors, a diagnostic controller and visualization tools so that users can to detect and fix air problems early. The company estimates optimizing application of pneumatic components coupled with proper system maintenance can lower air consumption up to 60%. At that rate, return on investment averages around six months.

Energy-efficient design of pneumatic systems

Incorrect dimensioning leads to higher costs, a reduction in quality and other problems. Learn basic solutions for correct dimensioning using real examples in this two-day course that teaches planning and designing safe optimized pneumatic systems. Working with Festo ProPneu software you will understand relationships between pressure, load and speed. 


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