Ordliste
Pressure tightness — definition
A requirement that the part does not leak under a stated pressure — decided by freedom from porosity, not by the surface.
A pressure-tight part needs a section without connected porosity from the inside to the outside. Isolated pores are rarely the problem; the problem is pores lining up to form a leak path.
Tightness is therefore achieved in the casting, not in the finishing. Gating design, venting, even wall thickness and the right solidification sequence are the tools.
If the part has to be pressure tight, three things have to be in the specification: what pressure, what medium, and what leak rate is acceptable. Must be tight is not a requirement that can be verified.
If you have a tightness requirement, raise it early in the enquiry — it affects both the tool design and the inspection that has to be agreed.