To facilitate the interchangeability of valves from different manufacturers, port hole patterns are internationally standardised, i.e. the arrangement of the outlet bores on a valve that must match the bores in the mounting subplate is standardised. This is the case for directional valves in DIN 24 340 Form A and ISO 4401 and for pressure, flow and check valves in DIN 24 340 Form D or E and ISO 6264 (Figure A 20).
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