Pneumatic & Hydraulic Control Valves

Control valves across 13,871 listed configurations — single-seat and cage-guided globe bodies, DN15 to DN300, ASME 150 to 600, with pneumatic or electric actuation. Compare and submit an RFQ.

Sourcing at a Glance

Standards / Certifications

IEC 60534, ASME B16.34, ANSI/FCI 70-2 (seat leakage classes)

Specifying Control Valves: Body, Trim, Leakage Class and Failure Mode

Control valves are sized on process data, not pipe size. This is a common specification error. The valve is selected so that the required flow sits within a controllable band of travel at the available pressure drop; a valve chosen to match the line diameter will typically be oversized, operate near the seat, cycle its trim and wear out early. IEC 60534-2-1 provides the sizing equations for incompressible and compressible flow, and IEC 60534-2-4 the inherent characteristics — linear, equal percentage, quick opening — that decide how stem travel translates into flow.

Body style. Single-seat globe bodies seat the plug directly: simplest construction, tightest shutoff, best for clean fluids and moderate pressure drop. Cage-guided bodies surround the plug with a cage whose windows set the characteristic; the cage is replaceable, so the same body can be re-trimmed, and specialised cages address cavitation and aerodynamic noise at high differential. Both are listed.

Size, class and connection. DN15 to DN300 across 13,871 configurations, in ASME 150, 300 and 600 plus PN16 and PN40, flanged throughout. ASME B16.34 supplies the pressure-temperature rating behind each class.

Materials. Carbon steel A216 WCB is the general process body; SS316 (CF8M) handles corrosive service; A352 LCB covers low-temperature duty below the −29 °C Charpy threshold; A217 WC6 chrome-moly is the high-temperature grade, conventionally specified above roughly 425 °C. Listed trim is either SS316 bar (A479) or SS316 with Stellite 6 facing; the hard-faced option covers the larger part of the range and is the trim carried on every lapped-metal (FCI Class V) seat in the catalogue.

Leakage class is a specification, not a quality grade. ANSI/FCI 70-2 Class IV permits up to 0.01 % of rated capacity through a closed metal-seated valve; Class V is the practical metal-seat limit, measured volumetrically; Class VI is the soft-seat bubble-tight grade, tested at 3.5 bar (50 psi) with air or nitrogen and expressed in bubbles per minute — 1 bubble/min at a 1-inch port rising to 45 at 4 inches. Classes V and VI use different measurement units and cannot be compared number-for-number. The catalogue offers metal seat (Class IV), lapped metal seat (Class V) and PTFE soft seat (Class VI). Specifying Class VI on a hot or abrasive service that will destroy a PTFE seat is a false economy — match the class to what the fluid allows.

Actuation and failure mode. Listed actuators are pneumatic spring-diaphragm in fail-close and fail-open action, pneumatic piston fail-last, and electric motorised fail-last. The failure position follows from the process hazard, not from convenience; it is a hard specification point alongside actuator torque or thrust. Spring-diaphragm actuators give an inherent, spring-driven failure position; piston and electric actuators generally hold last position unless a dedicated fail-safe device is fitted.

Positioners. From none (direct 3–15 psi) through pneumatic, electro-pneumatic 4–20 mA, integral electric and smart digital HART. Beyond accuracy, smart units provide travel histograms, friction trending and valve signatures that turn a control valve into a monitored asset. Match to the control-system signal type first.

Testing and conformity. IEC 60534-4 covers inspection and routine testing for control valves up to Class 2500. For export: PED 2014/68/EU category and module with CE marking, SABER for Saudi Arabia, ECAS for the UAE, EN 10204 3.1 certificates, and NACE MR0175 where the service is sour.

From spec to RFQ. Send: fluid and its properties, minimum/normal/maximum flow, inlet pressure and pressure drop at each, temperature, line size and class, required leakage class, failure mode, signal type, and destination market. A datasheet with three flow cases is worth more than any amount of description — share it with the RFQ and sizing is confirmed against the catalogue directly.

How Control Valves Work

Mechanism: a positioner-driven actuator converts a control signal into a metered flow area. "The opening or closing of control valves is usually done automatically by electrical, hydraulic or pneumatic actuators," with the valve itself manipulating "a flowing fluid, such as gas, steam, water, or chemical compounds, to compensate for the load disturbance." "The actuator is the device connected to the valve through the valve stem that provides the force required to move the valve," and on the most common design, "as the supply air pressure is increased, the rubber diaphragm pushes against the spring and moves the valve stem down into the valve body." The positioner is what makes this accurate rather than approximate: it does not drive the actuator directly but "relates the input signal and the valve position, and will provide any output pressure to the actuator to satisfy this relationship," continuously comparing actual stem position — sensed through a mechanical feedback arm linked to the spindle — against the position the controller has demanded, so that "there is a linear relationship between the signal input pressure...and the position of the control valve." Most process installations run this loop on a "4 to 20 mA DC signal," with building-services installations more commonly using "0–10 V."

Industries served: anywhere a process variable has to be held inside a working range without a person adjusting it manually. "Process plants consist of hundreds, or even thousands, of control loops all networked together to produce a product," each one holding "some important process variable such as pressure, flow, level, temperature, etc. within a required operating range" — the control valve is the final element that physically executes the correction each loop calls for. Sliding-stem globe and angle bodies are described as the most widely used design "because of rugged construction and the many options available that make them suitable for a variety of process applications, including severe service." Within a control loop, the valve is treated as "an example of a final control element," and by one account "the Control Valve is by far the most common final control element used in industry today" — a broad claim best read as directional rather than a specific industry list, but consistent with the range of fluids (gas, steam, water, chemical compounds) the same source names the device as handling.

Standards landscape: a shared terminology base underneath every other specification. IEC 60534 is not one document but a series, and its foundation is scope, not numbers: Part 1 "applies to all types of industrial-process control valves" and "establishes a partial basic terminology list and provides guidance on the use of all other parts of IEC 60534" — every later part, including the sizing equations and the routine-testing requirements the catalogue's own valves are checked against, inherits its definitions from that terminology base. That is the practical reason the standard is worth citing on a spec sheet at all: it is what makes "control valve," "actuator" and "positioner" mean the same fixed thing to a buyer and a manufacturer on opposite sides of an RFQ, rather than terms defined ad hoc by each maker. Sources: [RealPars — What Is a Control Valve? Types, Functions, and Applications Explained](https://www.realpars.com/blog/control-valve); [InstrumentationTools — Control Valve Working Principle](https://instrumentationtools.com/control-valve-working-animation/); [Spirax Sarco — Control Valve Actuators and Positioners](https://www.spiraxsarco.com/learn-about-steam/control-hardware-electric-pneumatic-actuation/control-valve-actuators-and-positioners?sc_lang=en-GB); [Wikipedia — Control valve](https://en.wikipedia.org/wiki/Control_valve); [IEC Webstore — IEC 60534-1:2023](https://webstore.iec.ch/en/publication/32585)

Frequently Asked Questions

Single-seat or cage-guided globe — which should I specify?

Single-seat globe valves seat the plug directly against the seat ring, giving direct seating and the simplest construction — the default for clean service and smaller sizes. Cage-guided valves guide the plug inside a cage whose windows define the flow characteristic, which makes the trim changeable, improves stability at high pressure drop, and allows anti-cavitation and low-noise cage designs. Both are listed catalogue families. State the pressure drop across the valve and whether cavitation or noise is expected — that is what usually decides between them.

What do FCI seat leakage classes IV, V and VI mean?

They quantify how much a closed control valve is permitted to leak, under ANSI/FCI 70-2. Class IV, the metal-to-metal grade, allows a maximum of 0.01 % of rated valve capacity. Class V is the practical limit for metal seats and is measured volumetrically. Class VI is the soft-seat, "bubble-tight" grade, tested with air or nitrogen at 3.5 bar (50 psi) differential with the outlet under water, permitting from 1 bubble per minute at a 1-inch port up to 45 at a 4-inch port. The catalogue maps metal seat to Class IV, lapped metal to Class V and PTFE soft seat to Class VI. Note that Classes V and VI use different units and are not directly comparable.

Fail-open, fail-close or fail-last — how do I choose?

The failure position is a process-safety decision made before any hardware choice: on loss of air or power, the valve must move to whichever state leaves the process safe — fuel valves usually fail closed, cooling-water valves usually fail open, and fail-last is used where holding the current position is safer than either extreme. The catalogue lists pneumatic spring-diaphragm actuators in fail-close and fail-open action, pneumatic piston fail-last and electric motorised fail-last. Fail-safe mode is a hard specification point — state it explicitly.

How are control valves sized?

On flow capacity, not on pipe size: the required Cv or Kv is calculated from the flow rate, the pressure drop across the valve and the fluid properties, then a valve is selected so that normal flow sits in the controllable part of its travel. IEC 60534-2-1 gives the standardised sizing equations for both incompressible and compressible fluids, and IEC 60534-2-4 defines the inherent flow characteristics — linear, equal percentage and quick opening — that determine how travel maps to flow. Supply minimum, normal and maximum flows with the corresponding inlet pressures and pressure drops in the RFQ; a single duty point is not enough to size a control valve.

Which positioner should I specify?

Listed options are none (direct 3–15 psi signal to the actuator), pneumatic, electro-pneumatic 4–20 mA, integral 4–20 mA electric, and smart digital with HART. A positioner improves stroking accuracy and speed and overcomes packing friction; smart digital units add diagnostics, valve-signature capture and remote calibration over HART. Match the positioner to the control-system signal and to whether asset-monitoring data is wanted.

What conformity documentation applies for EU, Saudi and UAE imports?

EU-bound pressure equipment is categorised under PED 2014/68/EU with CE marking per the applicable module; Saudi imports require SABER; UAE imports require ECAS; sour hydrocarbon service invokes NACE MR0175 on wetted parts. EN 10204 3.1 material certificates are the EU procurement baseline, and IEC 60534-4 covers inspection and routine testing for valves up to Class 2500.