A refinery, a subcritical power plant, a chemical tank farm and a chemical tanker all share one component in common: a set of industrial valves that decide whether the line runs safely or fails on first start-up. Walk the rack in any of those sites and you will find the same seven families of valves — gate, globe, ball, butterfly, check, plug and safety — just specified in different materials, classes and end connections.

The trap that catches new procurement teams is to treat a valve as a stand-alone item. In reality, a valve is a mechanical system: the body, the trim, the end connection, the companion flange, the gasket and the stud bolt all have to be specified together. Get the package right and the plant runs for decades. Get it wrong and the project loses weeks reconciling heat numbers and dimensions on site. This guide walks through each of the seven families in the order they are most often encountered on a process line.

Gate valves are the most common isolation valve in any refinery or cross-country pipeline. A wedge or gate lifts to open the line and drops to close it, giving a full-bore passage with almost no pressure ｄｒｏｐ when fully open. That is why gate valves are the first choice wherever the line is normally either fully open or fully closed, with very few throttling cycles in between.

For hydrocarbon service to API 600, the body is usually ASTM A216 WCB cast carbon steel with 13Cr or HF trim. For pipeline service to API 6D, the body is often A352 LCC or A216 WCC with full-bore or reduced-bore options. End connections are typically raised-face (RF) or ring-type joint (RTJ) flanges to ASME B16.5, with long-weld-neck flanges preferred on the line side to reduce turbulence at the valve inlet.

When a line has to regulate flow rather than just isolate it, the globe valve is the answer. The disc travels perpendicular to the seat, so the relationship between stem position and flow rate is predictable and repeatable. Pressure ｄｒｏｐ is higher than a gate or ball valve, but that is the point: the valve is designed to dissipate pressure in a controlled way.

Globe valves are the standard for feedwater regulation, start-up vent lines, chemical injection and by-pass circuits around control valves. In subcritical and supercritical power plants, the start-up vent and feedwater globe valves are commonly ASTM A217 WC6 or WC9 bodies, matched to P22 or P91 alloy pipe. For chemical service, A182 F316 stainless trim is a frequent choice.

Because globe valves change direction internally, the adjoining pipe fittings — usually elbows and tees — have to be dimensioned on the same drawing revision as the valve body, so the face-to-face and the tangent length line up at site.

The ball valve is the modern answer to many of the old roles of the gate and globe valve. A precision-machined ball with a through-bore rotates a quarter-turn between open and closed. Soft-seated ball valves achieve bubble-tight shut-off (Class VI), making them the default for gas service, steam manifolds and any hazardous fluid where leakage cannot be tolerated.

For oil and gas pipelines, ball valves to API 6D are the dominant choice, with full-bore variants used for pig-passing lines and reduced-bore variants on lateral connections. Bodies are commonly ASTM A216 WCB, A352 LCC or A351 CF8M for sour or chloride service. End connections are typically RF flanged, butt-weld (BW) for welded systems, or socket-weld (SW) for small-bore high-pressure branch lines.

When the line diameter goes above 24 inches and the budget cannot absorb the weight of multiple gate valves, the butterfly valve is the practical answer. A disc rotates 90 degrees inside the flow, giving a much lighter and shorter face-to-face than a gate or ball valve of the same size. Modern triple-offset designs (API 609 category B) achieve metal-to-metal sealing suitable for high-temperature and high-pressure service, so the old reputation of butterfly valves as “low-pressure only” no longer applies.

Butterfly valves dominate in cooling water lines, firewater systems, large-diameter air service, desalination plants and marine seawater cooling circuits. For marine and offshore cooling, a butterfly valve with a copper-nickel or aluminium-bronze body, paired with copper nickel flanges and Cu-Ni pipe to EEMUA 234, is a long-life combination that resists seawater corrosion.

Check valves are the silent protectors of a process line. They open when the flow is in the right direction and slam shut when flow reverses, protecting pumps, compressors and downstream equipment from water hammer and reverse flow. They are not operated manually; they are self-actuating.

The four common types are swing check, lift check, dual-plate (wafer) check and axial (nozzle) check. Swing checks are the workhorse for pump discharge and low-to-medium viscosity liquids. Dual-plate wafer checks are compact and common in refinery and chemical service. Axial nozzle checks are used in compressor and high-pressure gas service where slam and water hammer must be minimised.

For a refinery pump discharge, a swing check with ASTM A216 WCB body and 13Cr trim on RF flanged ends is typical. For a compressor discharge in a gas plant, an axial non-slam check with API 6D certification is the safe choice. In every case, the check valve sits between two flanged joints, so the pipe flanges and the stud bolts must be specified at the same time as the valve body.

Plug valves use a cylindrical or conical plug with a bored passage to control flow. They are robust, easy to lubricate and well suited to frequent operation, which is why they are common in oil and gas production manifolds, tank farm lines and slurry service. A lined plug valve (PTFE or PFA liner) handles aggressive chemicals; a metal-to-metal seated plug handles hydrocarbons and steam.

Plug valves are typically supplied with flanged or butt-weld ends, in carbon steel, stainless steel or nickel alloy bodies. They are a strong alternative to ball valves for abrasive or viscous service where a soft-seated ball would be damaged quickly. The trade-off is higher torque to operate, which often requires a gear operator or actuator on larger sizes.

No process line is permitted to operate without a code-stamped pressure relief device. Safety valves (for compressible fluids, spring-loaded) and relief valves (for liquids, spring or pilot operated) are the last line of defence when instrumentation and control loops fail. They are not optional and they are not interchangeable: a steam boiler requires a safety valve sized and certified to ASME Section I, while a refinery pressure vessel requires a relief valve certified to ASME Section VIII.

For oil and gas transmission pipelines, API 520 and API 521 define the sizing and the selection rules. For chemical reactors, the relief device is often sized for the runaway reaction case, not for normal operation — a calculation that the valve supplier has to be involved in from the early stages of the project. The relief valve inlet and outlet piping must be on the same drawing as the vessel, the valve and the rupture disc if one is fitted.

The table below summarises where each of the seven valve families is the right default choice. It is a starting point, not a substitute for a detailed datasheet. Every line in a process plant has its own combination of fluid, temperature, pressure and maintenance philosophy, and the final spec has to reflect that.

EZ STEEL INDUSTRIAL has been producing pipe, fittings, flanges and industrial valves from a single integrated facility in Hunan, China since 1994. The practical effect for a project is that a buyer can release a single purchase order that covers the valve, the pipe fittings, the pipe flanges, the gasket and the stud bolts — all on one MTR pack, one freight shipment and one delivery slot.

• One heat, one MTR pack. The valve body, the flange forging and the pipe can be ordered from the same heat batch, so heat-number reconciliation at site is reduced to a single cross-check.
• One drawing revision. Face-to-face, flange facing, fitting tangent and stud bolt length are designed on the same CAD model, so version conflict between the four product groups is eliminated.
• One QA system. API, EN, ASME and ISO 9001 audits are run on a single production line with a single QA manager accountable across all four product groups, which simplifies third-party inspection visits.
• One delivery slot. The four product groups land on the same truck, so welders and fitters are not waiting on a partial delivery while the valve sits in port clearance.

For refinery, power plant and marine newbuild projects — the same projects served by the China West-East Gas Pipeline and the South-to-North Water Diversion Project — this bundled approach is not a procurement slogan. It removes the four to six weeks of coordination time that usually separate a valve delivery from the rest of the piping package.

Use this list at the RFQ stage. If a line cannot be answered, the specification is not yet complete and the supplier will return a clarification request that delays the order by a week.

• Service fluid, concentration, and operating temperature / pressure (design and normal)
• Design code: API 600, API 6D, API 602, API 608, API 609, or ASME B16.34 — stated explicitly
• Body and trim material, with NACE MR0175 if sour service or ASTM A262 if austenitic stainless
• End connection: RF or RTJ flanged, butt-weld, socket-weld or threaded, matched to the adjoining flange or fitting
• Pressure class (ASME Class 150 to 2500) and face-to-face dimension to ASME B16.10
• Companion flanges, fittings, pipe schedule and material grade, all called out on the same drawing revision
• Gasket type, stud bolt grade and length, supplied with the valve so the joint can be assembled on arrival
• Test scope: hydrostatic, seat, low-pressure air, fire test (API 607 / API 6FA) — certificates to EN 10204 3.1
• Delivery terms: a single shipment covering valve, fittings, flanges, gaskets and studs, with one MTR pack and one point of contact