Compressed Air Best Practices - May 2008 - (Page 29)

Compressed Air Industry AUTOMOTIVE ASSEMBLY | 05/08 | Two of the four centrifugal manufacturers do not need buffer air for their single labyrinth seal design. They may employ an air driven venturi vacuum generator or ejector. This uses about 16 cfm at 30 psig but is not required for start up. The venturi vacuum generator or ejectors are used to pull a vacuum on the oil sump to eliminate oil migration and optimize oil flow. These air operated ejectors can be replaced with an electric driven model by at least one manufacturer. Control Air: If identifying the probable buffer air is somewhat complex, so too is identifying the control air. All centrifugal compressors will require this in some manner to start with some exceptions. Most of the units in the field have pneumatic operated control valves for the inlet guide vanes or an inlet butterfly valve and the blow off valve. There may be some other standard operating pneumatic operated control valves on some models. The air flow required to operate these is very low when in new operating condition; i.e., no leaks — no blown seals — no ruptured diaphragms — etc. One manufacturer sets this minimum volume at 10–25 cfm and this is probably very accurate. Depending on the design, the pressure requirement can vary from 40 to 80 psig. If all the valves are in the closed position, the start up can possibly occur at much less flow and pressure. However, good sizing would allow for higher pressure to activate the valves and enough air to handle a few leaks and worn valves — i.e. 25 cfm @ 80 psig. New units can all be ordered with electric operated valves if desired. Pneumatic valves can also be changed to electric operated in the field, but all things considered, this may not be very practical. Many operators perceive pneumatic valves more reliable than electric and feel pneumatic Venturi valves are much less prone to sudden failure. Other compressed air demand that may also exist on the unit being started: Cabinet cooling — Many factory packages (particularly in older units with hard wiring and/or solid state controls) will come with an air operated vortex type refrigerated cabinet cooler installed on the control cabinet. These will generally use 15 to 30 cfm of air at pressures from 50 to 80 psig. Applied correctly, they should use the highest pressure with Oil-free and Worry-free Compressed Air. 24/7/365. Aggreko has the experience and expertise to develop the 100% oil-free compressed air solution to meet your needs. We provide equipment and services to manage the risk of compressed air system failures, prevent downtime in production and supply backup systems to keep operations on schedule. Best of all - we’re available 24/7/365. Aggreko’s Rental Solutions include: The Right Rental Solution. Right Now. Power Generation Temperature Control Oil-Free Compressed Air 866.684.5568 www.aggreko.com www.airbestpractices.com 29 http://www.aggreko.com http://www.airbestpractices.com

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Compressed Air Best Practices - May 2008 Contents From the Editor Utility-Air News The Compressed Air Audit of the Month Pneumatics Real World Best Practices Delta Industries: Doing What is Right for Customers Delta Industries: Six Truths You Need to Know about Really Putting the Customer First Power Supply Industries Resources for Energy Engineers Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - May 2008

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