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Imitation is the sincerest form of flattery

Serck’s design ingenuity led to both life extension and performance enhancement on transmission & hydrostatic oil coolers for Diesel Multiple-Unit Fleets at Unipart Rail.

The Challenge

Serck Heat Transfer designed and built fixed tubestack coolers for the range of DMU vehicles introduced into service in the 1980s and 1990s.

After a long service life, these started leaking in service over 20 years ago. Many of those coolers which are still in service are failing. There are very limited repair options and many coolers have been scrapped.

Commercial production of these coolers stopped over a decade ago.

The Solution

Serck Heat Exchange designed, developed, tested and manufactured an ingenious repair solution for the complete range of the DMU fleet (150, 159, 166, 14X, 15X).

The old tubestacks were cut out of the existing cast shells, the shells were machined, then floating tubestacks were made and inserted into the old shells. Finally, Double O-rings were used to seal the tubestack to the shell. The repair solution passed test rig & field trials and a “comfort letter” was obtained from an independent engineering consultancy. Many of these “conversion repairs” have been in service since 2000 with an excellent service history.

The Result

The benefits of this repair have proved to be;

  • No vehicle modification; some models are easier to fit than original
  • Thermally more efficient then original; 1.5% at 80 litres/min and 3.5% at 120 litres per min on back to back tests
  • The floating stack is of a stronger construction in is isolated from vibration by the O-rings. The tubestack is free to grow/ expand at temperature, leading to a longer service life
  • The floating stack can be removed from the shell, examined and replaced
  • 90 10 copper nickel tubes have a better resistance to acid in the oils at running temperature and to coolant side erosion than copper


In fact, this innovative solution has been so successful that the design has been copied on DMU rail fleets throughout the UK.

If you have any questions about this project, or would like to know more about how we can help with your heating and cooling needs, contact us today.

The Floating TubeStack solution. Pioneered by Serck; copied nationwide