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Quotes - Engineering - Sales| CONSTRUCTION | WALLS | VENT | SERIES |
| Double Wall | Two | To atmosphere | DSU / DWU / DTCS / DTCW |
Double-Wall Design Requirements
What the Code Is Actually Asking For
The requirement behind double-wall construction is straightforward: where a non-potable fluid heats potable water, a single tube wall failure must not put one into the other undetected. Double-wall construction satisfies it by providing a second barrier and venting the space between them.
The vent is the essential feature. Two walls without a vented path between them would still allow a leak to migrate. The vent leads to the tube end, outside the pressure boundary of both fluids, so any leak discharges where it can be seen rather than accumulating.
Codes vary. The requirement appears in plumbing codes, health regulations and local amendments, and the authority having jurisdiction interprets it. Two neighbouring jurisdictions can take different views on the same installation.
It applies to tank heaters too. A bundle inside a potable storage tank is arguably the more critical case, because a failure discharges directly into stored water. The DTCS and DTCW ranges provide double-wall tank bundles.
Naval brass tubesheets. The DSU and DWU ranges use naval brass rather than the steel or brass found on the single-wall equivalents, which is one of the more reliable ways to identify genuine double-wall construction.
Double-Wall Construction Detail
Two walls in intimate contact, a vented path between them, and separate catalogue number ranges.
Construction
- Tube walls: Two, intimate contact
- Vent: To atmosphere at the tube end
- Tubesheet: Naval brass on DSU and DWU
- Bundle: Removable U-tube
Catalogue Ranges
- DSU in the 5-262 range
- DWU in the 5-267 range
- DTCS in the 5-272 range
- DTCW in the 5-277 range
- Not interchangeable with single-wall
Confirm With
- The authority having jurisdiction
- Local plumbing code
- Health regulations if applicable
- Your own quality system
- The project specification
Related
APPLICATION • POTABLE
Double-Wall Protection
The application view of the same requirement.
+ Learn MoreEstablish the Requirement Early
Ask the Authority, Not the Catalogue
Double-wall requirements are interpreted locally, and the same duty can be treated differently in adjacent jurisdictions. The catalogue can tell you what construction is available; only the authority having jurisdiction can tell you what is acceptable.
That conversation costs nothing before the order and a great deal at inspection, because a single-wall unit installed where double-wall is required cannot be signed off and cannot be converted.
It Changes the Physical Size
The interface between the two tube walls is a real thermal resistance, so a double-wall unit needs more surface for the same duty and the catalogued ranges top out at smaller shell diameters.
On a duty near the top of the double-wall range that can mean two units where one single-wall unit would have served, and it is worth knowing before the plant room is laid out.
