Valves get ordered by diameter and price more often than anyone admits. Five questions catch nearly every mis-selection before it is bolted into the line.
1. Isolate or modulate?
Ball and gate valves isolate; globe valves modulate. Throttling with a half-open ball valve destroys the seat within months.
2. What exactly is the medium?
Temperature, chemistry and solids content decide body and trim materials. The cheapest valve that survives is cheaper than the cheapest valve.
3. What pressure class — including surges?
Water hammer can multiply static pressure several times over. Rate for the transient, or fit protection and rate for reality.
4. How often will it operate?
A valve cycled daily needs different stem, seat and bearing design than one operated twice a year. Say so on the inquiry.
5. Manual or actuated — and what happens on failure?
If remote control matters, decide fail-open, fail-closed or fail-in-place now. Retrofitting actuators costs more than specifying them.
