Isolation valve selection: gate vs ball vs butterfly vs diaphragm
What "isolation" asks of a valve
An isolation valve is opened or closed, not modulated: it should seal tightly in the closed position, pass flow with minimal resistance when open, and move between the two states at a rate the system tolerates. Four families in this catalogue cover most isolation duties, and they differ in how they achieve the seal, how fast they operate, and what media they tolerate.
The four families, one paragraph each
Gate valves move a wedge or gate perpendicular to flow: full-bore, straight-through, low pressure drop, bidirectional — the default for larger-diameter isolation where slow operation is acceptable and throttling is not (a partly open gate vibrates and erodes). Rising-stem and non-rising-stem variants trade position indication against stem height.
Ball valves rotate a bored sphere a quarter turn: fast operation, tight shutoff, full-bore versions keep pressure drop near pipe level. Floating-ball executions seat on the downstream side and suit smaller diameters; trunnion-mounted balls take the seat load off the ball for larger diameters and higher classes. Multi-piece and three-piece bodies exist for maintainability; jacketed bodies keep media that solidifies at ambient temperature molten.
Butterfly valves rotate a disc a quarter turn inside a short body: the most compact and lightest per DN, standard in water works and utility service. Wafer executions clamp between flanges, lug executions allow upstream detachment; single-, double- and triple-offset geometry progressively reduce seat friction and improve tightness toward high-performance and process duties.
Diaphragm valves isolate the medium from the moving parts entirely: a flexible diaphragm — rubber or PTFE — is the closure and the corrosion barrier at once. Weir-type bodies suit general corrosive duty; straight-through bodies handle slurries and fibrous media that would lodge on a weir. The body can stay humble (cast/ductile iron) while the lining and diaphragm carry the corrosion duty.
Reading the published executions side by side
The table aggregates the model pages this catalogue publishes per family: how many identifier pages exist and which body material groups their spec tables evidence. Each linked family page lists the executions with their own size, pressure, material and standards tables.
| Family | Body materials evidenced on published model pages |
|---|---|
| gate-valve | Alloy Steel, Alloy steel, F11, F51, F53, Low Alloy Steel, Low-Temperature Steel, Low-temperature steel, Nickel Alloy Steel, Nickel base, Titanium alloy steel, carbon/low-alloy steel, cast iron, ductile iron, duplex, stainless steel |
| ball-valve | 1.4401/304, 1.4404/316L, A182 304, A182 304L, A182 316, A182 316L, A182 F51, A182 F53, Alloy 20, Alloy steel, F11, LC1, LCC, LF2, carbon/low-alloy steel, cast iron, duplex, nickel-molybdenum alloy, stainless steel |
| butterfly-valve | 5A, Alloy Steel, Bronze, CI, Chrome-moly steel, Copper, DI, Low-temperature steel, Nickel alloy, Titanium, carbon/low-alloy steel, cast iron, ductile iron, duplex, iron-nickel-chromium alloy, nickel-chromium alloy, nickel-copper alloy, nickel-molybdenum alloy, stainless steel |
| diaphragm-valve | carbon/low-alloy steel, cast iron, ductile iron |
Decision shortcuts and their limits
Coarse rules of thumb — gate for bidirectional large-diameter isolation, ball for quarter-turn tight shutoff, butterfly where weight and face-to-face matter, diaphragm where the medium attacks metal — are useful to shortlist, but the executions inside each family differ as much as the families do: a pressure-seal gate valve and a knife gate share a name, not a duty. The published execution pages and their comparison pages carry the actual differences; treat family-level rules as the first filter only.