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Design News, March 2013

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The Truth About Compressed Air! If you think compressed air is too expensive and noisy - read this. The facts will surprise you! Compare these Blowoffs Facts about Blowers There are a variety of ways to blow the water from the bottles shown in the photo below, but which method is best? To decide, we ran a comparison test on the same application using four different blowoff methods: drilled pipe, flat air nozzles, Super Air Knife (each using compressed air as a power source), and a blower supplied air knife (using an electric motor as a power source). Each system consisted of two twelve inch long air knives. The following comparison proves that the EXAIR Super Air Knife is the best choice for your blowoff, cooling or drying application. Energy conscious plants might think a blower to be a better choice due to its slightly lower electrical consumption compared to a compressor. In reality, a blower is an expensive capital expenditure that requires frequent downtime and costly maintenance of fi lters, belts and bearings. The goal for each of the blowoff choices was to use the least amount of air possible to get the job done (lowest energy and noise level). The compressed air pressure required was 60 PSIG which provided adequate velocity to blow the water off. The blower used had a ten horsepower motor and was a centrifugal type blower at 18,000 RPM. The table at the bottom of the page summarizes the overall performance. Since your actual part may have an odd configuration, holes or sharp edges, we took sound level measurements in free air (no impinging surface). Here are some important facts: Filters must be replaced every one to three months. Belts must be replaced every three to six months. Drilled Pipe Blower Air Knife Typical bearing replacement is at least once a year at a cost of nearly $1000. Th is common blowoff is very inexpensive and easy to make. For this test, we used (2) drilled pipes, each with (25) 1/16" diameter holes on 1/2" centers. As shown in the test results below, the drilled pipe performed poorly. The initial cost of the drilled pipe is overshadowed by its high energy use. The holes are easily blocked and the noise level is excessive - both of which violate OSHA requirements. Velocity across the entire length was very inconsistent with spikes of air and numerous dead spots. The blower proved to be an expensive, noisy option. As noted below, the purchase price is high. Operating cost was considerably lower than the drilled pipe and fl at air nozzle, but was comparable to EXAIR's Super Air Knife. The large blower with its two 3" (8cm) diameter hoses requires significant mounting space compared to the others. Noise level was high at 90 dBA. There was no option for cycling it on and off to conserve energy like the other blowoff s. Costly bearing and fi lter maintenance along with downtime were also negative factors. t Blower bearings wear out quickly due to the high speeds (17-20,000 RPM) required to generate effective airflows. t Poorly designed seals that allow dirt and moisture infiltration and environments above 125°F decrease the one year bearing life. t Many bearings can not be replaced in the field, resulting in downtime to send the assembly back to the manufacturer. Flat Air Nozzles As shown below, this inexpensive air nozzle was the worst performer. It is available in plastic, aluminum and stainless steel from several manufacturers. The flat air nozzle provides some entrainment, but suffers from many of the same problems as the drilled pipe. Operating cost and noise level are both high. Some manufacturers offer flat air nozzles where the holes can be blocked - an OSHA violation. Velocity was inconsistent with spikes of air. EXAIR Super Air Knife The Super Air Knife did an exceptional job of removing the moisture on one pass due to the uniformity of the laminar airflow. The sound level was extremely low. For this application, energy use was slightly higher than the blower but can be less than the blower if cycling on and off is possible. Safe operation is not an issue since the Super Air Knife can not be dead-ended. Maintenance costs are low since there are no moving parts to wear out. Blowers take up a lot of space and often produce sound levels that exceed OSHA noise level exposure requirements. Air volume and velocity are often difficult to control since mechanical adjustments are required. To discuss an application, contact: EXAIR Corporation 11510 Goldcoast Drive Cincinnati, Ohio 45249-1621 (800) 903-9247 Fax: (513) 671-3363 email: techelp@exair.com www.exair.com/14/423a.htm The Super Air Knife is the low cost way to blowoff, dry, clean and cool. See the Super Air Knife in action. www.exair.com/14/akvideo.htm Blowoff Comparison Comp. Air Type of blowoff PSIG BAR SCFM SLPM Horsepower Sound Purchase Required Level dBA Price Annual Electrical Cost* Approx. Annual Maintenance Cost First Year Cost Drilled Pipes 60 4.1 174 4,924 35 91 $50 $4,508 $920 $5,478 Flat Air Nozzles 60 4.1 257 7,273 51 102 $208 $6,569 $1,450 $8,227 Blower Air Knife 3 0.2 N/A N/A 10 90 $5,500 $1,288 $1,500 $8,288 Super Air Knife 60 4.1 55 1,557 11 69 $534 $1,417 $300 $2,251 *Based on national average electricity cost of 8.3 cents per kWh. Annual cost reflects 40 hours per week, 52 weeks per year.

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