Technical Hub

Choosing a control valve size is a calculation followed by a judgement. The calculation gives the flow coefficient the duty demands, and the judgement picks a valve from the manufacturer table whose rated coefficient puts the operating points in the right part of the travel. An undersized valve cannot deliver the maximum flow, and an oversized one spends its life…

In a petrochemical reactor the chemistry sets its own rules about temperature, and the control system exists to keep the process inside them. Exothermic reactions release heat that must be removed as fast as it appears, or the temperature climbs, the reaction accelerates and the situation turns into a runaway. Endothermic reactions need a steady supply of heat, and many…

Boilers and distribution mains run at pressures and temperatures chosen for efficiency, while most processes need steam at far milder conditions. Between the two sits the reduction station, and getting it right matters more than the piping around it suggests. Throttling steam to lower the pressure leaves the temperature almost unchanged, since the expansion is close to isenthalpic, so a…

Storage tanks hold liquids that have to stay clean, stable and safe for weeks or months at a time, and the space above the liquid is where most of the trouble starts. When the tank breathes, moist air gets in, oxygen reacts with the product, vapour escapes and is lost, and with flammable liquids a flammable atmosphere can form. Nitrogen…

How a control valve is installed decides how reliably it runs for the rest of its life. A valve mounted in the right place, oriented correctly, supported properly and protected from pipe strain will control accurately for years. The same valve, installed carelessly, will hunt, leak and fail early. These practices prevent most of the field problems we see. Choose…

When a control valve stops responding, the fault can sit anywhere in the loop: the signal, the positioner, the air supply, the actuator or the valve itself. The fastest way to find it is to walk the chain from the control signal down to the final element, rather than swapping parts and hoping. Check the Control Signal Start at the…

Cavitation and flashing are among the most common ways a control valve gets destroyed. Both happen when a liquid is throttled below its vapor pressure, and both erode the trim and body so fast that a valve can fail within months. Knowing what causes them, how they differ and how to prevent them is basic survival knowledge for high-pressure-drop service.…

Picking a control valve is really a sequence of decisions, and each one depends on the ones before it. Skip a step and you can end up with a valve that is too small, unstable at the operating point, or unable to shut off when it should. The eight steps below, taken in order, produce a specification you can verify…

The leakage class of a control valve sets the maximum leakage allowed past the plug and seat when the valve is closed. Standards such as FCI 70-2, ANSI B16.104 and IEC 60534-4 define six classes, I to VI, with increasingly tight limits. The right class is a balance between shut-off requirements, the media and cost. The Six Classes The classes,…

The actuator is the part of a control valve that moves the plug. It converts the control signal into stem travel, and its behavior sets the response speed, precision and reliability of the loop. Three types dominate: pneumatic, electric and self-operated. The right one depends on the energy available on site, the response and accuracy you need, fail-safe requirements and…