The Velan bimetallic trap was introduced in the 1950s, but still is one of the more recent developments in trap design. The fixed orifice trap first was used in the 1850s, while the initial patent on a thermodynamic trap was taken out in the U.K. in 1878. Armstrong International, Three Rivers, Mich., pioneered the inverted bucket trap in 1911. Other popular trap types, such as the thermostatic bellows and capsule designs, arrived on the scene later, although still a long time ago in relative terms.
Bestobell Steam, Cincinnati, Ohio, for example, introduced the Delta Element trap more than 40 years ago. Karl Lutkewitte, product manager, says the single-blade bimetallic design was aimed at correcting “two age-old steam trap problems: inherent steam loss and steam loss on trap failure.” He points out that the traditional inverted bucket trap — “the workhorse for the steam industry for decades” — vents some steam, albeit a very small amount, with each cycle/discharge of the trap. Disc traps also lose live steam with every discharge and these losses can rapidly increase as the cyclic operation degrades the disc’s seating surface.
“By contrast,” says Lutkewitte, “bimetallic thermostatic/thermodynamic steam traps and some thermostatic bellows and capsule traps don’t lose or use any live steam during operation.” This is because they do not cycle to discharge condensate, but instead modulate the condensate flow at a rate relative to its formation. This smooth modulating action, coupled with fewer moving parts, results in the Delta Element trap lasting three to four times longer than traditional cyclical discharge traps, claims Lutkewitte.
Spotting problems early
But, as Lutkewitte says, steam traps do wear out at some point. Unfortunately, users don’t always recognize when that occurs. “Traps that have failed completely open are easy to detect but the object is to find failing traps before they fail completely,” explains Gary Mohr of UE Systems. “Ultrasonic testing can do that. Technicians who use ultrasonic detectors on a daily basis can achieve accuracy [of detection] that exceeds 98%.”
One such detector is the hand-held TM5 ultrasonic and temperature-testing instrument that forms part of TLV’s TrapMan computerized trap-management system. The other part is TrapManager software, which enables extensive data analysis of a plant’s entire trap population. By comparing the test results obtained from the instrument with stored data from TLV’s laboratory analysis of similar traps in a controlled environment, the system is said to be able to diagnose trap performance within 15 seconds, an obvious attraction to plants that number their traps in the thousands. In its automatic referencing mode, the TM5 can be used by personnel with little trap-testing experience or training, TLV says.
Later this year the company plans to introduce to North America the PT1 Pocket TrapMan, a compact diagnostic instrument, also based on ultrasonic and temperature detection, that will enable the more skilled technician to make quick basic judgments as to the condition of traps and valves. The small hand held device can store the results of up to 100 trap/valve and 100 bearing inspections in its internal memory. TLV already offers PenCheck, a pocket-PC-based management system for small- to medium-sized populations of up to 1,000 traps.
Other steam trap monitoring and management systems on the market include the TrapMaster software from Yarway, Blue Bell, Pa., the SteamEye and SteamStar systems from Armstrong International, and Bestobell’s Steam Tector 2 hand held ultrasonic leak-detection device.
Claiming to offer the world’s widest range of steam traps — comprising the six main trap designs in sizes from 1/4 in. to 4 in., pressures to 1,940 psig, and capacities to 300,000 lb/h — Spirax Sarco, Blythewood, S. C. and Cheltenham, U.K., employs its own STMS computerized steam-trap management system to conduct plantwide trap surveys for customers. Failed traps are highlighted and steam losses automatically calculated to give payback times for replacements of the failed traps.
Sensors right at the trap
Spirax Sarco currently is involved in a collaborative project to develop an acoustic performance sensor that will be low enough cost to make it viable for attaching to most traps on the market, according to Richard Carmichael, head of central research in the U.K. That’s for the future, but for now the company’s equally innovative Pivotrol PTF4 condensate pump has been proving its worth on many condensate recovery systems (Figure 1). “This was designed in response to specific customer requirements,” says Carmichael, “such as high reliability and low maintenance, because if the condensate pump fails, the whole steam system fails.”
Figure 1. Reliable unit is crucial for keeping the whole steam system from failing.
One sensor that already is mounted on a trap itself is Yarway’s SmarTrap. Designed solely for the company’s Series 711/721 UniBody Plus disc traps, which are used on light loads such as steam tracing, the non-invasive electronic SmarTrap monitor comes permanently attached to the bonnet of the trap or its replacement capsule. Two LEDs (red and green) on the monitor alert inspection personnel in the area to the trap’s condition without them having to check the trap itself.
Inspectors need not be in the field, though, with Armstrong’s SteamEye system (Figure 2) for remote trap monitoring. “The basis of the system is a wireless transmitter — using either ultrasonics or conductivity monitoring — that reports to a receiver in a central location in the plant; this then web-enables the information to report on the plant’s intranet system,” says Tom Henry, the company’s director of global marketing. “What it reports is the condition of the trap at every moment of its operation.”
Figure 2. Wireless sensor and software enable monitoring of all steam traps from plant intranet.
Mounted just upstream of the inlet of any make or style of steam trap, SteamEye detects fluctuations in steam flow and temperature and, working in tandem with the web-enabled SteamStar “measurement platform,” can give remote warning of a failing trap. “Users can log on from anywhere in their company’s network through a password-protected interface,” explains account manager Chris Gibbs, “and monitor via the Internet the performance of their traps from an individual site or a host of different global sites.”
Armstrong plans to extend the SteamEye/SteamStar principle to additional points of monitoring around the steam system, notes Henry. “We’re looking at safety relief valves and monitoring condensate pumps,” he explains, “so you will know instantly the moment a condensate pump fails and begins to back up condensate.”
“There is a general trend in chemical plants at the moment to look at using wireless equipment to monitor plant equipment and provide more information on actual operating conditions,” says Henry, echoing what CP recently reported, (Where is wireless going?). Armstrong’s system is certainly capable of that, although DuPont’s Dvorak sounds a note of caution about automatic monitoring in general. “We do use ultrasonic detectors and automated diagnostic devices from several of the leading suppliers,” he says, “but with caution. That’s not to knock any particular product. It’s to maintain a principle whereby we believe that the people doing the testing need to know what it is they’re testing. The technology is great but they are tools — they should not be the mindset. It’s up to the user to understand why the device is there and how it is functioning.”
All the users — and suppliers — then have to do, of course, is convince others of the benefits these tools and good steam-system management in general can bring to the overall energy efficiency of the plant. But, like steam traps themselves, that’s an old, old story.