Another often-ignored hard metric is bore (nominal inner diameter). Pressure decides whether it holds; bore decides whether it flows. At the same pressure, an undersized bore still makes the system "throw tantrums" — just not as a burst, but as lost efficiency and rising heat.
Bore decides flow and pressure drop
At a given system pressure differential, bore directly affects achievable flow and pressure loss. Choose the bore too small and fluid velocity rises, lifting line friction — a chain of consequences: actuators starved and slower; the system heating up and oil temperature climbing; energy use increasing. That is why some equipment has "enough pressure yet sluggish action" — the culprit is often bore, not pressure. (Low-drop design is the product side's craft; on the selection side, the first thing is simply not to undersize the bore.)
Match by spec, not by feel
Hoses form a specification system by nominal bore (DN), and bore must correspond one-to-one with fittings, component ports and system flow. Mature selection back-calculates bore from flow and allowable pressure drop, rather than eyeballing "close enough." A slightly larger bore takes more space and weight but often pays off in high-flow, long-line duty; too small and you miscalculate efficiency and heat.
Pressure and bore, two ledgers together
A truly right selection is "pressure match + bore match," both passing: pressure enough but bore too small gives low efficiency, high heat and slow action; bore enough but pressure too small is a direct safety hazard. Add the bend radius of Article 6 and the medium and temperature above, and hose selection has always been a combination problem, never a single-item check.
Beyond pressure, bore is another ledger that must be settled. Read the two together, and hose selection is truly "right."
