Valve selection goes wrong when the type is chosen before the duty is defined. Start with what the valve has to do, and the type follows almost automatically.
There are only three things a valve is ever asked to do: isolate, regulate, or prevent reverse flow. Every valve type is optimised for one of them and compromised at the others. The single most common — and most expensive — mistake in valve procurement is using an isolation valve to throttle, which destroys the seat and turns a tight shutoff valve into a leaking one within months.
Start with the function
| Requirement | Right choice | Why |
|---|---|---|
| On/off isolation, low pressure drop | Gate or ball valve | Full-bore, unobstructed flow path when open |
| Throttling and flow regulation | Globe or control valve | Designed for partial opening and controlled trim wear |
| Quarter-turn, frequent operation | Ball or butterfly valve | Fast actuation, low operating torque |
| Prevent reverse flow | Check valve | Automatic, no external actuation |
| Positive isolation for maintenance | Double block and bleed | Verifiable zero-energy isolation |
Gate valves — isolation, and only isolation
A gate valve gives a straight-through bore with minimal pressure drop when fully open, and a tight metal-to-metal seat when fully closed. It is the workhorse of pipeline and refinery isolation. What it must never be used for is throttling: a partially open gate causes vibration, disc chatter and rapid seat erosion, and the resulting damage prevents tight shutoff for the rest of the valve's life.
Rising stem designs give a visual indication of position and are preferred where headroom allows. Non-rising stem is used where vertical clearance is limited or the stem must be protected from the atmosphere.
Globe valves — when you need to regulate
The tortuous path through a globe valve is exactly what makes it good at throttling and bad at pressure drop. Expect a significantly higher permanent head loss than a gate valve of the same size. Accept it where flow control matters — steam service, chemical dosing, bypass lines — and avoid it on long runs where pumping energy dominates.
Flow direction matters on a globe valve. Installing it against the marked direction changes the seating behaviour and can cause the disc to slam. Check the body arrow at installation, every time.
Ball valves — fast, tight, and torque-sensitive
A quarter turn takes a ball valve from fully open to fully closed, with bubble-tight shutoff from a soft seat and negligible pressure drop in a full-bore design. That speed is also the hazard: rapid closure on a long liquid line generates surge pressure that can exceed the design rating of the pipe. On large-bore liquid service, gear operators or actuators with controlled closing time are not optional.
- Full bore where pigging is required or pressure drop must be minimised.
- Reduced bore where cost and weight matter more than head loss.
- Floating ball for smaller sizes and lower pressures; trunnion-mounted above roughly 6" and Class 600.
- Soft seats (PTFE, PEEK) for tight shutoff; metal seats where temperature or abrasive media rule soft seats out.
Check valves — the ones that get least attention
Check valve failures are common because sizing is often ignored. An oversized check valve never fully opens, so the disc flutters continuously against the stop and fails by fatigue. Size the valve for the actual flow velocity, not the line size, and select the type for the installation orientation.
Swing checks suit horizontal lines with steady flow; lift and piston checks suit higher-pressure and vertical applications; dual-plate wafer checks are compact and close quickly, which limits reverse-flow slam on pump discharge.
Double block and bleed for positive isolation
Where maintenance requires verified isolation — breaking containment on a hydrocarbon line, entering a vessel — a single valve is not sufficient regardless of its condition. DB&B provides two seating surfaces with a bleed point between them, so the cavity can be drained and monitored to prove that neither seat is passing. It is the difference between assuming isolation and confirming it.
A closed valve is an assumption. A drained and monitored bleed between two closed seats is evidence.
Specifying the rest of the valve
Type is only the first decision. A complete valve specification also fixes:
- 1Pressure class to ASME B16.34, checked against design pressure at design temperature — not at ambient.
- 2Body and trim materials matched to the fluid, including NACE MR0175 compliance for sour service.
- 3End connections — flanged, butt weld, socket weld or threaded — consistent with the line specification.
- 4Seat leakage class and any fugitive emission requirement to ISO 15848.
- 5Operation: handwheel, gear, or actuator with fail position defined for the process safety case.
- 6Fire-safe certification to API 607 or API 6FA where hydrocarbons are present.
Our stock position
We supply gate, globe, check, ball, motorised and control valves in carbon steel, stainless and alloy trims, in the classes and sizes the Eastern Province's plants consume routinely. Send us the line specification and duty conditions and our valve desk will return a type and material recommendation with a stock position against it.
Technical Desk
Valves & Flow Control
