20929 Bridge Street, Southfield, MI 48033 4121 Brockton Drive SE, Grand Rapids, MI 49512 6200 Baron Drive, Bridgeport, MI 48722 6910 Treeline Drive, Suite A, Brecksville, OH 44141 Serving the industry since 1927 Phone: (800) 589-6120 - Fax: (248) 354-3710 www.deppmann.com April 13, 2009 ~ Monday Morning Minutes: Lifting Condensate From a Heat Exchanger Over the last several we’ve examined trap sizing out of a heat exchanger or coil with a modulating control valve. In a low pressure application the pressure available to the steam trap is the elevation from the heat exchanger outlet to the trap inlet. Often the gravity return main is overhead and there is a temptation to lift the condensate out of the trap and into the return. Any lift on the outlet of the trap causes a back pressure on the trap which must be overcome by inlet pressure at the trap. The back pressure caused by lift is approximately 1 PSIG for every 2.4 feet of condensate lift. Clearly if we only have 14” or ½ PSIG at the inlet to the trap and we need the ½ PSIG to pass the condensate out of the trap, there is no pressure available for lift. Condensate will back up into the heat exchanger or coil and steam hammer will destroy the coil. Never lift out of a heat exchanger or coil with a modulating control valve in low pressure applications. Run the condensate to a gravity drain without lift or add a condensate pumping unit. You may hear that bucket traps or inverted bucket traps are “lifting” traps. Whether F&T or inverted bucket, steam traps do not lift. There is no motive source in a normal trap. The reason inverted bucket traps are referred to as lifting traps is because they are less prone, not immune, to damage caused by steam hammer. Assume we have a coil without a modulating valve and 15 PSIG steam available. There is enough pressure in the heat exchanger to overcome the trap pressure drop and some lift to an overhead gravity return main. The concern in this case is over hammer. The condensate at the trap is at about 15 PSIG and 250°F. As the condensate rises in the discharge pipe, the pressure drops. At some point the pressure is not great enough to keep the condensate in a liquid state and it flashes into steam. The volume change from water to gas is huge and there may be hammer in the discharge pipe. The hammer will collapse the ball in an F&T trap. The open bucket in an inverted bucket trap can rattle and might get damaged but the bucket does not collapse. This is why the bucket type trap is often referred to as a lifting trap. In general, regardless of pressure, in modulating controlled heat exchangers avoid lifting out of the steam trap. Thank you for using products sold by R. L. Deppmann Company in Michigan and Ohio! Disclaimer: R. L. Deppmann and it’s affiliates can not be held liable for issues caused by use of the information on this page. While the information comes from many years of experience and can be a valuable tool, it may not take into account special circumstances in your system and we therefore can not take responsibility for actions that result from this information. Please feel free to contact us if you do have any questions.
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