General rules
Ducts and fittings for cleanroom HVAC must meet high-pressure requirements for class N1โN5 or medium-pressure for N6โN9, and should be fabricated and cleaned in a covered, enclosed, dust-free area.
Fabrication and sealing
- Rectangular ducts up to 900 mm must not have a spliced bottom plate; larger ducts avoid transverse joints, and N1โN5 systems forbid snap-lock seams.
- Inner surfaces stay smooth with no internal stiffeners or reinforcing ribs.
- All gaps are sealed with sealant; after washing, ends are capped and stored clean.
- Installation starts only after the floor is done and dust control is in place; opened ends are resealed if work pauses.
Leakage and HEPA filters
Field-assembled units pass a leakage test: N1โN5 allow no more than 0.6% and N6โN9 no more than 1.0%. HEPA filters are installed only after finishing, piping and 12 h of continuous commissioning, with correct orientation and sealed, secure joints.