Hydrostatic proof of a liquid engine: cooling circuits can be plugged and proofed, propellant manifolds cannot without a blanking plate

Easy mistake when planning (or visualising) a water proof-test bench for a regeneratively or water-cooled engine: treating every circuit the same, i.e. feed one port with a hand pump and plug the others. That only works for closed circuits such as coolant channels (inlets and outlets are the only openings). A propellant manifold is open to the combustion chamber through the injector orifices, so plugging its other ports does not seal it and it will not hold proof pressure. Proofing a manifold needs a blanking plate in place of the injector (or a separate manifold-only fixture), which is extra hardware to plan and budget.

Related checks that came up in the same review: - Proof pressure basis: use 1.5x the pressure a relief valve is certified fully open at, not its set pressure (e.g. set 700 psig, full open 770 psig gives 1,155 psig proof). Confirm the test facility’s required factor before buying a hand pump; 2x can exceed a 1,500 psi pump. - SAE straight-thread (O-ring boss) fittings and plugs ship with nitrile/FKM O-rings, which do not seal at LN2/LOX temperatures and are not oxygen-compatible; cold ports need metal boss seals or spring-energised seals proved cold. - Parts that carry LOX during cold flow (not just hot fire) need oxygen cleaning before that test.