How to Calibrate a Control Valve: Step by Step Procedure

Control valve calibration verifies that the valve, actuator, positioner, and control signal work together correctly across the required operating range. A proper calibration checks valve travel, input signal, actuator response, zero, span, intermediate positions, and repeatability.

For a pneumatic control valve, calibration may involve checking the actuator bench setting first, followed by valve stroke checking and positioner calibration. For a smart positioner, the procedure can include automatic setup, input signal verification, valve travel calibration, and final linearity checks.

The exact procedure depends on the valve type, actuator, positioner, signal range, fail action, and manufacturer instructions.

8 Steps Procedure to Calibrate Control Valve

This below Step by Step control valve calibration procedure provides a thorough explanation of how to calibrate a control valve using reference standards.

What Should Be Checked Before Control Valve Calibration?

Before starting control valve calibration, verify the valve tag number, valve datasheet, actuator details, positioner model, signal range, fail action, required instrument air pressure, and calibration tolerance.

The technician should confirm whether the valve is:

• Linear or rotary
• Pneumatic or electric
• Direct acting or reverse acting
• Air to open or air to close
• Single acting or double acting
• Equipped with a pneumatic positioner or smart positioner
• Configured for a standard or split range signal

Also verify the required input signal. A pneumatic positioner may use a 3 to 15 psi signal, while a modern smart positioner commonly receives a 4 to 20 mA signal.

Never assume the signal range or valve action. Confirm the values from the valve and positioner datasheets before making adjustments.

Which instrument is used to calibrate control valve?

Step 1: Prepare the Tools required for control valve calibration

Tools Required for Control Valve Calibration

The exact tools required depend on the type of control valve and positioner. Typical equipment includes:

• Calibrated pressure gauge
• Pneumatic pressure regulator
• Portable pressure calibrator
• 4 to 20 mA loop calibrator
• HART communicator for smart positioners
• Instrument air supply
• Digital multimeter
• Test leads
• Appropriate pneumatic tubing and fittings
• Hand tools
• Valve position indicator or travel scale
• Manufacturer calibration manual
• Control valve datasheet
• Instrument data sheet
• Calibration report or test sheet

All reference instruments should have valid calibration certificates and suitable measurement ranges for the test being performed.

Step 2: Safety Precautions

Calibration Setup

Before beginning the calibration of the control valve, we need to make sure that the actuator bench setting has been verified.

Step 3 : Prepare the Setup for bench setting of control valve

Step 4 : Verify the bench setting of control valve 

1. Bench set is the term for the initial compression that a spring adjuster applies to the actuator spring.
2. The lower bench set defines the force available and the pressure necessary to start the valve-opening movement for air-to-open valves.
3. The lower bench set establishes the pressure necessary to start the valve-closing movement for air-to-close valves. Pressure applied less bench set less spring compression from travel determines seating force.
4. The spring angle may vary somewhat as a result of spring tolerances.
5. The bench set requires the most accuracy once the valve has been seated. For information on how to modify the spring, see the manufacturer’s instructions.
6. The instrument air pressure needed to completely stroke the actuator over its entire range and to start moving the stem against its closure spring is known as an actuator bench-set.
7. The spring compression is changed to compensate for the process pressures that will be applied on the plug region when these settings are made.
8. Before the actuator is installed onto the valve and, this adjustment is normally made.

Bench setting procedure

1. Anchor the actuator with a vice and load the actuator diaphragm temporarily.
2. Valve positioner and stem connector need to be removed before starting the procedure.
3. Provide a certified pressure gauge (PG) that can properly measure the diaphragm pressure from zero to the upper bench set pressure shown on the actuator name plate.
4. Temporarily apply and alter actuator loading pressure using a pressure regulator.

1. Make that the actuator stem is positioned as shown in the above figure at the top of its travel. Diaphragm loading pressure should be set at 0 psig.
2. Slowly increase the pressure from 0 psig to the lowest bench set pressure while monitoring for actuator stem movement.
3. At the lower bench set pressure, the actuator stem should be moving.
4. If movement is sensed either before or after the lower bench set pressure is attained, slide the spring adjuster into or out of the yoke until the actuator stem movement is first detected there.

1. Make sure the spring adjuster is set to the stated specifications.
2. Apply pressure on the diaphragm equal to the top bench set loading pressure. The actuator stem is extended towards the valve by this pressure.
3. Keep in mind that, as indicated above, the actuator stem may move over the valve stem.
4. Use a marker or cello tape to mark the valve stem at the actuator stem’s end.
5. If the actuator stem does not pass over the valve stem, you must indicate this point of stem travel.
6. Diaphragm loading pressure should be gradually reduced until the lowest bench set pressure is used.
7. Measure the distance from the end of the actuator stem to the marking or tape on the valve stem.

1. The distance must be equal to the travel span shown on the scale of the travel indicator.
2. Bench set adjustment is finished if the travel span is accurate. The valve and actuator may then be connected to one another with stem connector. Also the positioner need to be installed back.
3. In the event that the span is not accurate, either the spring has been damaged in some way or the incorrect spring has been fitted on the valve actuator.

Step 4 : Prepare the Setup for calibration of control valve with positioner

As shown by the connection diagram, connect the control valve and its calibration accessories.

Step 5 : Calibration of Control Valve with Positioner

The following process is for calibrating a control valve that is equipped with a pneumatic positioner.

1. When the control valve bench set has been finished, the positioner should then be installed.
2. In order to calibrate the automated control valve with a pneumatic Positioner, an air regulator is inserted and then set at an air supply of 20 PSI.
3. Adjust the Regulator until the pressure meets the specifications shown in the datasheet for the positioner.
4. For the purpose of simulating the signal pressure of 3-15 PSI, connect and utilize a fine precision regulator, which then delivers an opening/closing signal to the valve.
5. When applying the 3 PSI signal, the valve must be at 0% of stroke length.
6. If it is not entirely closed, you may modify the position of the valve using the zero adjustment in Positioner.
7. When applying the 15 PSI signal, the valve must be at 100% of stroke length.
8. If it is not entirely opened, you may modify the position of the valve using the span adjustment in Positioner.
9. These procedures will be performed as many as required until the valve movement accurate values, i.e., open and close parameters.
10. Typically, a position transmitter will be placed with the control valve. So, using the position transmitter’s feedback mA, the stroke length could be measured. It could have converted into valve movement in %
11. The intermediate positions will be checked once the 0% and 100% percentages have been adjusted.
12. You will need to perform the method of calibration as many times as necessary until the control valve is calibrated to the appropriate tolerance.
13. Depending on the specific control valve positioner and kind of control valve being utilized, the calibration process may change. Please read the manufacturer’s instructions before starting, then.

Control Valve Linearity and Hysteresis Test

A control valve calibration should not be considered complete after checking only the 0% and 100% endpoints. Intermediate positions should also be verified.

Linearity

Linearity testing compares the actual valve position with the expected position at different input signals.

For example, if 12 mA corresponds to 50% command, the actual valve position should be within the specified calibration tolerance.

Hysteresis

Hysteresis is identified by comparing valve position during increasing and decreasing input signals.

For example, the valve may reach one position when the signal increases to 12 mA and a slightly different position when the signal decreases back to 12 mA.

Large differences can indicate mechanical friction, packing problems, actuator issues, positioner problems, or other valve assembly conditions.

Record both upscale and downscale results in the calibration report.

Step 6: Recording Calibration

1. Do linearity tests in the upscale and downscale directions at 0%, 25%, 50%, 75%, and 100% to make sure the control valve is stroking appropriately.
2. If the output value does not fall within stroking an acceptable range, calibration is required. Once again, if the output values have deviated from the permitted range, a control valve has to be serviced or replaced.
3. No extra calibration is required if every output value (+/- %) falls within accepted limits.
4. The output data should be entered into the as found/as left column of the blank calibration report.

Step 7: Completion of Calibration

1. When the calibration has been successfully completed, attach the calibration label to the control valve.
2. When the calibration is complete, clean the apparatus, store it somewhere safe, and record the calibration information for future use.
3. Disconnect the regulators, pressure gauge, and other equipment.
4. Reinstall the control valve in the processing area.
5. Make sure the workplace is tidy.
6. De-isolate the equipment.
7. Restore the signal’s usual level once it has been bypassed or inhibited.
8. Put the control valve back into use and check that it is operating normally once you have done so.

Step 8: Calibration Report Preparation

In the workshop using the information gathered during the calibration, prepare the calibration report. The following picture displays how the control valve calibration sample report was completed in the field or a workshop using a pressure regulator and a standard pressure gauge as the reference.

The Excel template that was used to make the control valve calibration report can be downloaded from the link below.

What Should a Control Valve Calibration Report Contain?

A control valve calibration report should provide enough information to identify the valve, test equipment, calibration conditions, and final results.

The report should normally include:

• Valve tag number
• Valve manufacturer
• Valve model
• Valve size
• Actuator details
• Positioner model
• Input signal range
• Supply pressure
• Valve fail action
• Valve travel
• Calibration date
• Reference instrument identification
• Reference instrument calibration status
• As found results
• As left results
• Upscale results
• Downscale results
• Calibration error
• Acceptance criteria
• Technician name
• Reviewer or approver
• Calibration status

The completed report should be retained according to the site’s instrument maintenance and quality procedures.

Calibration Standards for Control Valves

Standards and guidelines that offer suggestions and instructions for calibrating control valves. One commonly used standard is:

ISO 5208: General Principles for Control Valve Calibration:

Provides guidelines on test equipment, procedures, and reporting for control valve calibration.

IEC 60534: Calibration of Electropneumatic Positioners:

Specific to electropneumatic positioners, covering zero and span adjustments, hysteresis, and repeatability.

ASME B16.34: Dimensions for Flanged Butterfly Valves:

Focuses on face-to-face and end-to-end dimensions, crucial for calibrating butterfly valves.

ANSI/ISA-S75.19.01: Calibration of Control Valves in Process Industries:

Designed to the process industry, addressing test procedures, acceptance criteria, and reporting.

The calibration procedure for the control valve was developed based on reference from NIST standards, ensuring adherence to precise measurement principles and traceability to recognized calibration practices

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Frequently Asked Questions About Control Valve Calibration

What is control valve calibration?

Control valve calibration verifies that the control signal produces the correct valve travel or position across the specified operating range.

How do you calibrate a control valve?

The typical procedure includes checking the actuator, stroke, positioner, zero, span, intermediate positions, and upscale and downscale response.

What is the calibration range of a control valve?

The range depends on the valve and positioner configuration. Common pneumatic signals include 3 to 15 psi, while modern electronic positioners commonly use 4 to 20 mA.

How do you calibrate a control valve positioner?

Apply the specified input signal, verify valve travel, adjust zero and span when required, and repeat the test until the valve position is within the specified tolerance.

What is zero adjustment in a control valve?

Zero adjustment establishes the correct valve position at the lower end of the input signal range.

What is span adjustment in a control valve?

Span adjustment establishes the correct valve travel between the lower and upper signal limits.

How do you check control valve stroke?

Apply the specified actuator or positioner input and compare actual stem or shaft travel with the valve’s specified travel.

What are the control valve calibration test points?

Common test points are 0%, 25%, 50%, 75%, and 100%, tested in both increasing and decreasing directions.

Why does a control valve fail to reach 100%?

Possible causes include incorrect span adjustment, insufficient actuator pressure, incorrect configuration, mechanical restrictions, incorrect bench setting, or positioner problems.

Why does a control valve not fully close?

Possible causes include zero adjustment problems, mechanical obstruction, packing friction, incorrect fail action, actuator problems, or valve seat problems.

What is control valve hysteresis?

Hysteresis is the difference in valve position observed at the same input signal when the signal is approached from increasing and decreasing directions.

Can a smart positioner calibrate a control valve automatically?

Many smart positioners provide automatic setup or calibration functions, but the exact procedure depends on the manufacturer and model.

What should be recorded in a control valve calibration report?

Record the valve identification, test equipment, input signals, expected positions, actual positions, errors, upscale and downscale results, acceptance criteria, and as found/as left condition.

What is the difference between valve calibration and positioner calibration?

Valve calibration verifies the complete valve assembly, while positioner calibration focuses on configuring the positioner to produce the required actuator response and valve position.