To size an industrial valve, provide the required flow rates, operating pressures, fluid temperature and properties, and the valve’s intended function. For control valves, the sizing engineer also needs the pressure drop across the valve at minimum, normal, and maximum flow; for isolation valves, line size, operating conditions, shutoff requirements, and actuator details are also important. Include connection, material, and applicable project requirements so the proposed valve suits the complete service—not just the pipe diameter.
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A valve should not be selected by matching its nominal size to the line alone. An oversized control valve may operate poorly at low flow, while an undersized valve may not deliver the required capacity. At Kaiwei, we recommend sending a process datasheet or completing the information checklist below so a supplier can identify missing inputs before proposing a valve.
Start by explaining what the valve must do in the process. A valve used for continuous flow control is sized differently from one that stays fully open or fully closed during normal operation. If the valve must perform more than one duty, describe each duty and identify which one governs the selection.
For modulating control, specify the flow range the valve must regulate and whether the process requires stable control at low, normal, and peak demand. For isolation service, state whether the valve is normally open or closed, how often it operates, and what shutoff performance the project requires. For emergency or safety-related duties, provide the defined operating requirement and applicable project documentation rather than relying on a general description.
Clarify whether the valve will open or close against a pressure differential and whether it must move to a defined position after loss of power, signal, or instrument air. These details affect valve construction and actuator selection. They also help distinguish the process sizing question from the mechanical question of whether the valve can operate under the specified conditions.
Flow and pressure data are central to valve sizing. Send the minimum, normal, and maximum expected flow, with units such as m³/h, L/min, kg/h, or Nm³/h. For gases, state the reference conditions used for any normalized or standard volumetric flow; otherwise, different reference bases can make flow figures difficult to compare.
Provide upstream and downstream pressure for the operating cases, not only the system’s maximum pressure rating. State whether pressure values are gauge or absolute, and include the expected pressure drop across the valve where it is known. As an illustrative example only, a datasheet might show 10 bar(g) upstream and 6 bar(g) downstream at a specified flow; these figures are not a sizing recommendation.
For a control valve, the pressure drop may change as flow changes or as other equipment operates. Share the relevant operating cases and identify whether downstream pressure is fixed, variable, or influenced by the valve. The sizing calculation may also need to consider limits such as vapor formation, flashing, cavitation, or choked flow, depending on the fluid and conditions.
Give the fluid’s name and state whether it is a liquid, gas, steam, or a mixture. Include the operating temperature range and any important changes in composition or phase during operation. A generic description such as “chemical” or “process gas” is usually insufficient for a responsible sizing review.
For liquids, useful data may include density or specific gravity, viscosity, vapor pressure, and solids content. For gases, provide molecular weight or specific gravity, compressibility information if available, and the temperature and pressure basis for the flow data. For steam, identify the steam condition and provide the relevant pressure and temperature information.
Also disclose corrosive, abrasive, toxic, flammable, or polymerizing characteristics, along with suspended solids or risk of crystallization. These properties can influence the body, trim, seat, and seal materials, as well as the valve type. If the exact fluid properties are unavailable, state what is known and ask the process or engineering team to confirm the missing values before final selection.
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Line size is important for interfaces and installation, but it does not by itself establish the correct valve capacity. Provide the nominal pipe size, piping class or pressure rating, and end connection type, such as flanged, threaded, or welded. If available, include pipe schedule, face-to-face limits, orientation, and space restrictions around the valve and actuator.
Identify the required body and internal materials, or provide the project material specification for review. State the design pressure and temperature, applicable codes or standards, and any documentation or inspection requirements specified by the project. Avoid assuming a material or standard based solely on the fluid name; service conditions and project requirements determine what is suitable.
For a control valve, describe the control signal, desired control behavior, and any positioner or accessory requirements already defined by the project. If the control system has a specified signal range, state it explicitly. Provide the required failure position—fail open, fail closed, or fail in place—where applicable, together with the available power or instrument-air conditions.
For actuated isolation valves, share the required operating time, cycle frequency, and whether manual operation is needed. The actuator must be evaluated against the valve’s operating requirements and the pressure conditions it will encounter. If the required torque or thrust is known, include its source; otherwise, the supplier may need to review the process and mechanical data to determine an appropriate actuator arrangement.
The table below is a practical starting point for a sizing request. Not every application requires every value, and the responsible sizing method depends on valve type and service. Mark unknown items clearly instead of entering estimates as confirmed data.
| Information | What to provide | Why it matters |
|---|---|---|
| Valve duty | Control, isolation, on/off, throttling, or other | Guides valve style and selection criteria |
| Flow | Minimum, normal, and maximum values with units | Defines required capacity and operating range |
| Pressure | Upstream and downstream values for each case; gauge or absolute | Establishes pressure drop and operating conditions |
| Fluid and temperature | Fluid name, phase, temperature range, and relevant properties | Supports sizing and material review |
| Connections and materials | Line size, rating, connection, and material specification | Checks piping compatibility and project requirements |
| Actuation and shutoff | Manual or actuated, failure position, signal, and shutoff requirement | Defines operation and actuator needs |
A valve that matches the line size may still be unsuitable for the required flow or control range. Provide actual process conditions and let the sizing review determine the appropriate valve capacity and configuration. Any reducer or expander arrangement should also be considered as part of the installation.
A single normal-flow value does not show how the valve performs at turndown or peak demand. Where possible, provide at least minimum, normal, and maximum cases, with the corresponding pressure and temperature. If only partial data are available, identify the assumptions that remain unconfirmed.
Values without units or a gauge-versus-absolute pressure basis can lead to incorrect interpretation. Use consistent units throughout the datasheet, and label any converted or normalized gas-flow figures. Confirm that the flow, pressure, and temperature values refer to the same operating case.
A clear inquiry helps a valve supplier assess the application, identify gaps, and discuss suitable valve and actuation options. At Kaiwei, we can review the information you provide and help clarify which additional process, connection, or operating details are needed for the next step. Final selection should be checked against the project’s process design, piping requirements, and applicable specifications.
To request a sizing review, send your process datasheet or the completed checklist, including all available operating cases. Flag estimates, unknown values, and any non-negotiable project requirements separately. This gives the supplier a practical basis to respond without treating assumptions as confirmed design data.
To size an industrial valve, provide its duty, minimum-to-maximum flow, upstream and downstream pressures, fluid properties, temperature range, and mechanical and control requirements. Include line and connection details, material requirements, shutoff expectations, and actuator conditions where applicable. The most useful next step is to assemble these values in a process datasheet, label units and pressure basis, and ask a qualified supplier to review any missing or uncertain inputs before finalizing the selection.
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