Total savings over the lifecycle of the packaging machine can surpass 30%, outweighing the incremental cost of enabling components.
By Steve Bain, Industry Segment Manager, Food and Packaging, Festo
Original equipment manufacturers reduce packaging machine air consumption by more than 30% while increasing the speed of their packaging machines by designing those machines with valve terminals close to cylinders and by making other design changes. Savings and performance benefits over the lifecycle of the machine dwarf the incremental cost of new enabling technology.
Wasted energy in compressed air tubing
Compressed air in the tube between the valve and cylinder does no work and wastes the energy needed to compress it. How much energy is wasted? Consider, for example, an ISO cylinder connected to a valve via 20 ft of tubing. Fully 75% of the total compressed air in the system is used to only fill the tubing, while 25% of the compressed air is in the cylinder doing work, as seen in Figure 1.
Decreasing the distance between valve and cylinder not only lowers compressed air usage, but it also increases the rate of cylinder response by speeding pressurization time. In other words, the shorter the tube, the faster the pressurization.
The solution for this tubing problem has been to mount a valve terminal on the machine as close to cylinders as possible while still making the terminal easily serviceable by maintenance technicians. A machine-mounted valve terminal provides for a median-tubing-length solution that balances distance with serviceability. Figure 3 shows a base machine with a centrally placed valve terminal, 12 cylinders, and tubing lengths of 10 ft.
Up until recently, it has not been cost effective to mount an optimum number of valve terminals closer to cylinders due to valve terminal size, the hardware cost of terminals, and networking nodes (i.e. EtherNet/IP) for the terminal. Furthermore, with more networking nodes, the PLC may also need to be upgraded to accommodate them, which is added cost to the machine.
Remote and decentralized I/O opens the door for energy savings
Recent advances in remote and decentralized I/O, including IO-Link and the Festo AP network, have led to the development of small, rugged, and lower-cost valve terminals that don’t each require an EtherNet/IP node. With this new generation of valve terminals all under a single EtherNet/IP node, additional terminals can be cost effectively spread throughout the machine as shown in Figure 4. Figure 5 shows how this new plug-and-play architecture shortens the distance between valve terminal and cylinder.
Separate, zoned valve manifolds reduce tubing lengths
There is a hardware cost to distributing valve terminals throughout the machine. But does that cost outweigh the benefits? The base machine shown in Figure 3 had a single valve terminal serving 12 cylinders with tubing length of 10 ft. By separating the valves and adding a second terminal, the 12 cylinders can be served by tubing of 8 ft and 4 ft, respectively, as seen in Figure 6.
The cost of adding a new generation smaller valve terminal to the base machine is 7%. This machine improves speed by 3% and lowers energy consumption by 14%. Over the machine’s lifecycle, the energy saved plus the speed improvements will provide a positive return for the 7% hardware investment.
Adding a third terminal to the base machine makes the longest tubing length 4 ft, as compared to 10 ft with the single valve terminal and 8 ft for the two-terminal machine. There is a 15% cost increase for the three-terminal solution compared to the base case. Bringing valves closer to cylinders in this scenario would lower compressed air energy cost by 26% and boost speed by 14%, as Figure 7 shows.
Lower pressure on the return stroke of the cylinder
All the work of the cylinder is typically with the extend stroke, where the maximum pressure must be exerted. Nearly every packaging machine uses the same pressure on the return stroke, which wastes energy because high pressure is not needed. A simple change to lower compressed air consumption is to reduce pressure into a valve’s Port 5 for the return stroke. Many valve terminals offer this reversal capability, where air is routed backwards through the terminal. A cylinder, for example, which uses 6 bar for the extending cycle may only need 4 bar on the return. A single regulator and a couple of fittings are all that is needed to achieve the savings.
Continuing from the previous three-valve-terminal example, lowering pressure from 6 bar to 4 bar on the return stroke increases energy savings from 26% to 36% while cost and speed remain unchanged, as indicated in Figure 8. Not every application can use less pressure, but it is incumbent on the designer to explore the possibility through proper sizing.
What pressure does the machine require?
Every pneumatics application encourages design engineers to add a little more compressed air than needed for the application because the extra force can compensate for changing conditions as the machine ages.
This doesn’t necessarily mean 6 bar is better than 4 bar or that 8 bar is better than 6. It does mean that an accurate design of the pneumatic system requires optimum sizing of cylinders and tubing for the job at hand and too much pressure than the application needs is not necessarily better.
Festo, for example, offers a free online engineering tool, Festo Pneumatic Sizing, where designers input the key application requirements of stroke, payload, and position time and the tool gives back component solutions in terms of eco-mode, adequate size, and performance design. The point of the three solutions is that there are no absolutes. The best solution is dependent on the OEM’s and end user’s goals and the environment the machine will inhabit.
With this flexibility in mind — no absolutes, but options — what energy savings can be had by using a pressure regulator to lower pressure, for example, from 6 bar to 4 bar without affecting performance?
Clean versus ultra-clean compressed air
Pneumatic manufacturers design their products to function at a company-standard air purity as measured in microns (µm). The minimum required air quality for pneumatic components can impact energy savings. Say, for example one supplier’s company standard for the recommended air purity of its cylinders is 5 µm while another is 40 µm (the Festo company standard). Systems operating at 5 µm require 8% higher pressure than one with 40 µm air purity. Over the life of the machine, an 8% savings by using components designed for 40 µm air purity level rather than 5 µm can be considerable, and there would be no disadvantage in terms of cylinder life.
The most exciting factor about the benefits of shortening tubing between valve and cylinder, reducing the air pressure in the system, lowering pressure on the return stroke, and finding an optimum air purity level is that these changes are relatively easy and cost effective to make when designing a machine. End users can play a role by specifying these design features. Using these design tips means that the higher the number of cylinders on a packaging machine, the greater the relative savings.
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