DSU Series Double-Wall Steam Heat Exchangers

Two Barriers Between Steam and Potable Water

A double-wall tube is two tubes drawn together, with a deliberate vented path between them. If either wall develops a pinhole, the fluid travels along that path and appears outside the unit rather than crossing into the other stream. A failure that would otherwise be silent becomes something you can see on a walk-round.

Where it is required. Wherever a non-potable heating medium warms potable water. Codes vary by jurisdiction and by the authority having jurisdiction, so it is worth confirming rather than assuming, but the requirement is common enough that the DSU exists as a catalogued range rather than an engineered special.

What it costs thermally. The interface between the two tube walls is a real thermal resistance, so a DSU needs more surface than an SU for the same duty. The catalogued range accounts for this and the unit is correspondingly larger. Substituting an SU part number for a DSU because the dimensions look similar is a mistake worth avoiding.

Naval brass tubesheets. The DSU range uses naval brass rather than the steel or brass tubesheets found on the standard SU. That reflects the potable-water service the unit is built for, and it is one of the details that distinguishes a genuine DSU from a visually similar SU.

Everything else is familiar. Removable U-tube bundle, cast iron bonnets, steel shell, 2, 4 and 6 pass tube-side arrangements, and the same 5-262 catalogue number structure encoding shell diameter, length and pass count.