Trappings of success
Steam traps come in all shapes and sizes. Some have a bucket arrangement going up and down in a casing. Others use a ball float arrangement in an enclosure. Their reliability varies considerably but they are all a drain on maintenance resources because they all fail. If a trap fails open it loses excessive amounts of steam. In fact, surveys have found that more than 40% of all steam traps jam, and estimate that the UK loses around £3bn of steam per year as a result. If, however, a steam trap fails closed it causes, at best, impaired heat output and productivity or, at worst, water hammer and explosions.
Invented by Tim Gardner and manufactured by Gardner Energy Management of Bristol, the revolutionary trap works by releasing a continuous flow of condensate from steam lines through a specially configured venturi orifice (see picture and diagram, above). Condensate, which is 1,000 times denser than steam, is ejected through the venturi but the column of condensate awaiting ejection holds steam safely inside the system. During warm-up, at first air and then cold condensate jet through the venturi. Once the system has warmed up, the condensate is hot and, as it passes through the trap, flashes as it encounters low pressure. The result is turbulent flow in the discharge throat, which increases resistance to flow through the trap and puts back pressure on the orifice. This gives the GEM trap dynamic performance over varying load: the lower the condensate load, the less the cooling of the condensate and the higher the discharge temperature. This increases the flash steam effect and so reduces the trap capacity.
The ETSU study, funded by the DETR as part of the Energy Efficiency Best Practice Programme, covers the traps' performance over one year at the laundry of Withington Hospital in Manchester, where continual and costly testing and replacement of steam traps had never managed to curb the growth of "an unsightly plume of some 500kg/hr of steam from the vent pipe on the condensate receiver, and associated energy losses". The study showed that, after replacing 11 of the 65 steam traps in the laundry with GEM traps, "the vent steam flow was down to 59kg/hr, an overall reduction of 89%." Annual savings totalled £10,350 (£8,570 on energy and £1,780 on treated water make-up) but, as Tim Gardner is quick to point out: "no allowance was made for savings in testing and maintenance costs within the simple payback analysis, and neither is steam usage per output of production considered, so real efficiency gains are often hidden."