A control valve specification converts process conditions and project requirements into the information needed to size, select and quote a complete valve assembly. The customer normally provides the service conditions, piping data and required operating behaviour. The valve supplier then calculates the required Cv, selects the valve and trim, sizes the actuator and confirms the final accessories.
Not every highlighted field on a control valve specification sheet is mandatory for every enquiry. Some fields are essential process inputs, some apply only when a particular accessory or project requirement is involved, and others can be marked “Supplier to recommend”. Separating these three categories prevents customers from guessing technical values that should be confirmed during valve selection.
This guide explains how to complete the highlighted fields, which information must come from the customer and which values should remain open for the control valve supplier to calculate or recommend.
What is a control valve specification sheet?
A control valve specification sheet, also called a control valve datasheet, records the design basis for one valve or a group of identical valves. It normally combines four types of information:
- Identification data: tag number, quantity, service and P&ID reference.
- Process data: fluid, temperature, flow rates, inlet pressures, outlet pressures and physical properties.
- Project requirements: pressure rating, connection, materials, leakage class, failure position, noise limit and hazardous-area requirements.
- Supplier selection data: calculated Cv, valve size, port size, trim construction, actuator sizing and accessory models.
The sheet is not simply a product order form. It is the technical basis for checking whether a proposed valve can pass the required flow, control the process at normal operation, withstand the shut-off condition and respond correctly after loss of air or electrical power.
A complete datasheet also makes quotations easier to compare. If different suppliers receive different assumptions about pressure, flow or failure action, their proposed valve sizes and prices may not be technically comparable.
How to complete the highlighted fields
The yellow cells in the current specification sheet should be treated as fields requiring customer attention, but they are not all unconditionally mandatory. A practical way to use the form is to classify each highlighted item as required, conditional or supplier to recommend.
Download the control valve specification sheet
Use the Excel template while following the instructions below. Complete the applicable customer-input fields and leave calculated valve-selection fields for the supplier to confirm.
Download the Control Valve Specification Sheet
| Highlighted field group | Recommended treatment | Explanation |
|---|---|---|
| Service and fluid name | Required | Identifies what the valve controls and helps determine the required materials and trim. |
| Fluid state and operating temperature | Required | Sizing equations and material limits depend on whether the fluid is a liquid, gas, steam or mixed phase. |
| Flow unit and minimum, normal and maximum flow | Required | The three cases are used to check maximum capacity and normal and minimum controllability. |
| Inlet and outlet pressures for each flow case | Required | Each flow case must have a corresponding upstream and downstream pressure. |
| Shut-off pressure | Required | Used for actuator thrust or torque sizing. It is not necessarily the same as the normal operating pressure drop. |
| Operating density and standard density | Conditional | Provide the properties relevant to the selected sizing basis. Standard density is mainly needed when gas flow is stated at standard conditions. |
| Pressure rating and connection type | Customer requirement or supplier confirmation | The customer should state the piping class when known. Otherwise, the supplier can recommend a rating based on design pressure and temperature. |
| Body, plug, seat and stem materials | Customer requirement or supplier recommendation | State mandatory project materials. If no material is prescribed, provide the fluid composition and corrosion or erosion conditions for selection. |
| Leakage class and flow characteristic | Customer requirement or supplier recommendation | Specify them when required by the process. Otherwise, the supplier should select them from the control duty and shut-off requirement. |
| Pneumatic and electrical connection sizes | Conditional | Complete these fields only for the applicable actuator, positioner or accessory and when the project has a connection standard. |
| Positioner explosion-proof and IP ratings | Conditional but important | Required when a positioner is included and the installation has a hazardous-area or environmental protection requirement. |
| Maximum noise level | Conditional | Complete it when the project specifies an allowable sound-pressure level. Do not invent a limit when none has been established. |
| Air failure position | Required for actuated valves | The required fail-open, fail-closed or fail-in-place action must come from the process safety review. |
| Remarks and face-to-face dimension | Conditional | Face-to-face dimensions are particularly important for replacement valves and fixed piping tie-ins. |
If a yellow field is outside the customer’s technical responsibility, it should not be filled with an arbitrary value. Enter “Supplier to recommend”, “By vendor” or “Not applicable” so the intention is clear.
Process data the customer must provide
The process data is the most important customer input because it determines the required flow capacity and exposes possible cavitation, flashing, choked flow, excessive velocity or noise. A supplier cannot correct an inaccurate operating case by selecting a different valve model.
Fluid name and composition
Use a specific fluid description rather than a general term such as “chemical”, “gas” or “water service”. State the concentration of mixtures, the presence of solids and any corrosive, toxic, abrasive or polymerising components. For steam, indicate whether it is saturated or superheated.
Fluid state
Identify the fluid as a liquid, gas, vapour, steam or two-phase mixture. Different sizing equations are used for liquids and compressible fluids. Two-phase service normally requires additional process information and a separate engineering review.
Operating temperature
Provide the temperature corresponding to the sizing condition. If the minimum or maximum design temperature affects the material, packing or seat selection, record those limits in the remarks or project data as well.
Minimum, normal and maximum flow rates
The three flow cases serve different purposes:
- Maximum flow: checks whether the selected valve has sufficient capacity.
- Normal flow: checks whether the valve operates in a suitable travel range during routine operation.
- Minimum flow: checks whether the valve can control the lowest required flow without operating too close to the closed position.
Always state the flow unit. For gas service, clarify whether the value is actual or referenced to standard or normal conditions, and identify the reference temperature and pressure where necessary.
Inlet and outlet pressures
Each flow rate must be paired with its own inlet and outlet pressure. The maximum flow does not automatically occur at the maximum inlet pressure, and the minimum flow does not automatically occur at the minimum pressure drop.
| Operating case | Flow rate | Inlet pressure | Outlet pressure |
|---|---|---|---|
| Maximum | Qmax | P1 at Qmax | P2 at Qmax |
| Normal | Qnor | P1 at Qnor | P2 at Qnor |
| Minimum | Qmin | P1 at Qmin | P2 at Qmin |
The pressure drop for each case is calculated from the matching values:
ΔP = P1 − P2
Do not combine the maximum inlet pressure from one operating condition with the minimum outlet pressure from another unless that combination represents a genuine process case.
Fluid properties
Liquid sizing commonly requires density or specific gravity and may also require vapour pressure, critical pressure and viscosity. Gas sizing may require molecular weight, compressibility factor, specific heat ratio and density at the stated reference condition.
These values should be taken from the process simulation, fluid datasheet or a recognised property source at the relevant operating condition. Estimated values should be clearly identified as estimates.
Shut-off differential pressure
The shut-off differential pressure is the highest differential pressure against which the valve may be required to close and maintain the specified leakage performance. It is used primarily for actuator sizing and trim force or torque calculations.
This value should be based on the credible upstream and downstream conditions when the valve is closed. It should not be copied automatically from the normal operating pressure drop.
Project constraints the purchaser should state
Process data determines what the valve must do. Project constraints determine how the selected valve must connect to the plant, withstand the environment and integrate with the control system.
Piping size, material and pressure class
Provide the line size, pipe material and piping class where available. The valve body size may differ from the line size, so reducers may be required. The valve pressure rating must be suitable for the design pressure and temperature, not only the normal operating condition.
Connection type and face-to-face dimension
State whether the valve requires flanged, butt-weld, socket-weld, threaded or another connection type. Include the flange standard and facing where applicable.
A fixed face-to-face dimension is not always required for a new installation. It becomes important when replacing an existing valve, connecting to prefabricated piping or working within a restricted installation envelope. In those cases, provide the existing dimension and drawing rather than relying only on the nominal valve size.
Mandatory materials
If the project piping specification requires a particular body or trim material, record it on the datasheet. Where the material is open to selection, provide enough service information for the supplier to review corrosion, erosion, temperature and galling risks.
Body material, plug material, seat material and stem material should not be selected independently without considering the complete trim combination and the actual fluid.
Seat leakage requirement
The required leakage class should be based on the process need. A more stringent shut-off class may require a different seat construction, additional actuator force or a soft seat with lower temperature and chemical limits.
Do not specify the tightest available class automatically. Excessive leakage requirements can increase cost and may introduce unnecessary limitations without improving process control.
Air-failure position
The customer must define the safe valve position following loss of instrument air or control signal. Typical requirements are fail closed, fail open or fail in place. This decision should come from the process safety assessment and cause-and-effect philosophy.
Failure position influences actuator type, spring direction, available thrust and the arrangement of accessories. It should not be selected solely from the valve’s normal operating direction.
Instrument air and electrical interfaces
When pneumatic equipment is used, state the available air-supply pressure and any required tubing connection size. For an electro-pneumatic positioner, provide the control signal, electrical entry size, hazardous-area certification and ingress-protection requirement.
Complete these fields only for the accessories included in the valve package. For example, positioner electrical requirements are not applicable to a valve without an electrical positioner.
Noise and environmental limits
If the project has a maximum allowable noise level, state the limit and the measurement basis. The valve supplier can then evaluate aerodynamic or hydrodynamic noise and determine whether a low-noise trim, diffuser or other treatment is required.
Also state ambient temperature, outdoor exposure, corrosive atmosphere, washdown requirements and any hazardous-area classification that affects the actuator or accessories.
Values the valve supplier should calculate or confirm
The following fields normally depend on engineering calculations or the construction of the selected valve. They should remain open unless the customer has a mandatory design requirement.
| Supplier output | What should be checked |
|---|---|
| Calculated Cv | Required Cv for the minimum, normal and maximum operating cases. |
| Selected or rated Cv | Available capacity of the proposed valve and trim. |
| Valve body and port size | Capacity, velocity, rangeability, piping geometry and available product sizes. |
| Valve opening | Expected travel at minimum, normal and maximum flow. |
| Flow characteristic | Process gain, system pressure-drop behaviour and required control range. |
| Trim construction | Cavitation, flashing, noise, erosion, pressure drop and shut-off duty. |
| Actuator size and spring range | Shut-off differential pressure, packing friction, seat load, air pressure and safety margin. |
| Actuator allowable differential pressure | Maximum differential pressure the selected assembly can safely control or shut off against. |
| Accessory models | Compatibility with signals, certification, supply pressure, response time and failure action. |
Calculated Cv and selected Cv are not the same
Calculated Cv is the flow coefficient required by a particular process case. Selected Cv is the rated capacity of an available valve and trim. The selected value normally exceeds the highest calculated requirement, but excessive oversizing should be avoided.
The calculated result should be treated as a sizing reference rather than a final valve selection. The supplier must still confirm the rated Cv, expected valve travel, body and port size, flow characteristic and any cavitation, flashing, choked-flow or noise limitations.
A valve that is much larger than required may spend normal operation close to the seat, where small stem movements produce large flow changes. This can cause unstable control, accelerated seat wear and frequent cycling.
Valve size should not be copied from the line size
The line size is an important piping input, but it does not automatically determine the control valve size. The selected valve may be smaller than the pipe if capacity and velocity checks permit. Conversely, severe service or a specialised trim may require a different construction.
The supplier should confirm the proposed body size, port size, reducers and allowable velocities as one system.
Actuator sizing is part of valve selection
An actuator should be sized against the actual valve forces or torque, maximum shut-off differential pressure, packing friction, required seat load, available supply pressure and failure action. Selecting an actuator from valve size alone can result in insufficient shut-off force or an unnecessarily large assembly.
Common control valve specification mistakes
Providing one flow rate only
A single design flow may be enough for a preliminary capacity check, but it does not show whether the valve can control normal and minimum operation. Provide minimum, normal and maximum cases whenever possible.
Using one pressure drop for all flow cases
System resistance and equipment operating conditions change with flow. Copying the same pressure drop into all three cases can distort the calculated Cv and the predicted valve travel.
Confusing operating pressure with shut-off pressure
The normal operating pressure drop is used for flow sizing. The shut-off differential pressure is used mainly for actuator and seat-load calculations. They should be evaluated separately.
Mixing gauge and absolute pressure
Clearly identify whether pressures are gauge or absolute. The datasheet shown uses MPa.G for operating pressures, but compressible-flow calculations may require absolute pressure. The supplier must be able to convert the stated values without guessing the reference basis.
Leaving gas-flow reference conditions undefined
Standard cubic metres, normal cubic metres and actual cubic metres are not interchangeable. State the reference temperature and pressure used for the reported gas flow.
Specifying materials without fluid composition
A material name alone does not demonstrate suitability. Fluid concentration, temperature, contaminants, solids and corrosion allowance may change the appropriate body and trim selection.
Requesting the highest leakage class by default
A stricter leakage class is not always a better specification. It can affect seat type, actuator force, temperature limits and cost. Select the class required to protect the process or equipment.
Choosing the failure position without a safety basis
Fail open and fail closed are process-safety decisions. The correct action depends on what happens to the plant when utility power or instrument air is lost.
Completing supplier fields by guessing
Customers sometimes enter a valve size, Cv, actuator model or spring range to avoid leaving a blank cell. Unless these values are mandatory project requirements, it is better to write “Supplier to recommend” and allow the complete assembly to be checked from the process data.
Standards and the control valve datasheet approval workflow
A control valve may be affected by several standards because sizing, body design, end connections, dimensions, leakage, noise and hazardous-area equipment are separate subjects. There is no single ASME standard that covers every part of a control valve assembly.
Commonly referenced documents may include the IEC 60534 or ISA-75 series for control valve terminology, sizing and performance; ASME B16.34 for valve body design requirements; ASME B16.5 for applicable flange dimensions and ratings; and ASME B16.10 for face-to-face dimensions. ANSI/FCI 70-2 or IEC 60534-4 may be referenced for seat leakage, depending on the project.
Special services may introduce additional requirements. Sour-service material restrictions, oxygen cleaning, fire testing, low-emission packing or customer-specific inspection requirements should be stated separately. The purchase specification should identify the required standard and edition rather than relying on a general note such as “according to international standards”.
Recommended datasheet workflow
- The purchaser completes the process inputs. This includes the fluid, operating temperature, flow cases, matching pressures and required physical properties.
- The purchaser states mandatory project requirements. These may include piping class, materials, leakage class, failure position, hazardous-area classification and accessory interfaces.
- The supplier checks data completeness. Conflicting units, missing pressure cases and unclear fluid properties should be resolved before final sizing.
- The supplier performs valve sizing and selection. The calculation should cover all stated operating cases and relevant noise, cavitation, flashing or choked-flow checks.
- The supplier completes the selected-valve fields. These include the valve type, size, port, rated Cv, trim, actuator, positioner and accessories.
- The purchaser reviews the proposed assembly. The review should compare the proposal with the process duty, piping specification, control philosophy and project standards.
- The approved datasheet becomes part of the order documentation. Subsequent changes should be revision-controlled so the final valve matches the approved technical basis.
Whenever a process value changes after sizing, the effect should be reviewed. A change in flow, pressure, temperature, fluid composition or shut-off condition may alter the valve size, trim or actuator selection.
Complete the specification before requesting a quotation
A control valve quotation is only meaningful when every supplier is working from the same operating conditions. Before sending the enquiry, check that the fluid, temperature, flow unit, minimum, normal and maximum flow rates, and the corresponding inlet and outlet pressures have been completed as a coherent set.
The purchaser should also state the shut-off pressure, required air-failure position and applicable connection, material, leakage, noise and instrument-interface requirements. Calculated Cv, valve size, port size, trim construction, actuator sizing and final accessory models can remain open for the valve supplier to calculate or confirm.
Once these inputs are ready, attach the completed control valve specification sheet and email it to [email protected] for technical review. This allows missing or conflicting information to be identified before the valve sizing and proposed assembly are finalised.