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Valve Stroke Time Calculator - Actuator Volume, Air Supply & Stroking Speed

Calculate valve open/close time based on actuator volume, supply pressure, positioner flow capacity, and tubing size

Estimate control valve and on-off valve stroke time from actuator volume, supply air pressure, and positioner or solenoid flow capacity. Enter actuator type (diaphragm, piston, scotch yoke), effective volume, supply pressure, and air delivery source to calculate open and close times. Accounts for tubing restrictions, booster relay capacity, and volume tank sizing for emergency shutdown (ESD) applications. Supports both throttling valves with positioners and on-off valves with solenoid pilots.

Pro Tip: On ESD valves, the stroke time measured during commissioning rarely matches the stroke time five years later. Packing friction increases, actuator seals degrade, and air supply components drift. Test ESD valve stroke time at every turnaround and trend the results. A valve that stroked in 3 seconds at commissioning and now takes 5 seconds is heading toward a failure-to-close event. Establish a maximum acceptable stroke time (typically 1.5x the design time) and pull the valve for maintenance when it exceeds that threshold.

Size the valve actuator for available air pressure

Valve Actuator Sizing Calculator →

Size the tubing to prevent flow restriction

Instrument Air Line Calculator →

Calculate the control valve Cv for proper sizing

Control Valve Cv Calculator →

Read the valve stroke time guide

Valve Stroke Time Guide →
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Valve Stroke Time Calculator
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How It Works

  1. Select Actuator Type

    Choose the actuator type: spring-diaphragm (most common for throttling valves), pneumatic piston (double-acting or spring-return), or scotch yoke (quarter-turn ball and butterfly valves). Each type has a different volume-to-stroke relationship.

  2. Enter Actuator Volume

    Input the actuator effective volume in cubic inches. For diaphragm actuators, this is the effective area times the stroke. For piston actuators, it is the piston area times the stroke. Manufacturer datasheets provide these values, or measure the physical dimensions.

  3. Define Air Supply

    Enter the supply pressure and the air delivery capacity of the positioner, booster relay, or solenoid valve in SCFM. The air delivery device is typically the bottleneck that determines stroke speed, not the supply header.

  4. Add Tubing Restrictions

    Enter the tubing size, length, and number of fittings between the air delivery device and the actuator. Long or undersized tubing runs add significant flow restriction that slows the stroke, especially on large actuators.

  5. Review Stroke Times

    See the calculated open and close stroke times. For spring-return actuators, the air-assisted direction is typically faster than the spring-return direction. The calculator flags when stroke time exceeds common safety requirements (10 seconds for ESD, 60 seconds for throttling).

Built For

  • Safety engineers verifying that ESD valve stroke times meet SIL requirements per IEC 61511
  • Instrument engineers selecting positioners and boosters to achieve target stroke times
  • Maintenance techs diagnosing slow valve response by comparing calculated vs measured stroke time
  • Commissioning engineers establishing baseline stroke time records during plant startup
  • Reliability engineers trending stroke time degradation to predict actuator maintenance needs
  • Project engineers specifying volume tanks and quick-exhaust valves for fast-acting ESD applications

Features & Capabilities

Multiple Actuator Types

Handles spring-diaphragm, piston (single and double-acting), and scotch yoke actuators with correct volume calculations for each. Quarter-turn actuators use swept volume that varies with rotation angle.

Air Delivery Device Modeling

Models the flow capacity of positioners, booster relays, solenoid valves, and quick-exhaust valves. Uses Cv or SCFM capacity ratings to determine the maximum air flow rate to or from the actuator.

Spring Return Analysis

Calculates both the air-fill stroke time and the spring-exhaust stroke time separately. The spring-return stroke is typically 1.5-3x slower due to limited spring force and exhaust flow restrictions.

Volume Tank Sizing

Sizes instrument air volume tanks (accumulators) for ESD applications where the valve must stroke on loss of air supply. Calculates the minimum tank volume to fill the actuator from stored pressure.

Stroke Time Trending

Provides a framework for recording and comparing stroke times over the valve's service life. Flags degradation that indicates increasing friction, leaking seals, or weakening springs.

Frequently Asked Questions

Valve stroke time is determined by three factors: the actuator volume that must be filled or exhausted, the flow capacity of the air delivery device (positioner, solenoid, booster), and the restrictions in the tubing between them. The actuator volume is fixed by the valve size and actuator selection. The air delivery capacity is the most common bottleneck. A standard positioner may deliver 5-15 SCFM, while a booster relay can deliver 50-100+ SCFM. For fast-acting requirements, the combination of delivery capacity and tubing size must be optimized together.
ESD valve stroke time requirements are defined by the safety integrity level (SIL) assessment and the process hazard analysis, not by a generic standard. Typical targets range from 2-10 seconds for fast-acting ESD valves in refinery and chemical service. The process safety time (the time available between a hazard detection and the point of no return) determines the maximum allowable stroke time. The valve stroke time must be less than the process safety time minus all detection and logic solver delays. Always verify the requirement in the project's safety requirement specification (SRS).
Packing friction directly opposes actuator force, reducing the net force available to accelerate the valve stem. Higher friction means slower acceleration and longer stroke time. New PTFE packing may add 50-200 lbs of friction on a 4-inch globe valve, but over-tightened or degraded packing can add 500-1000+ lbs. Graphite packing runs higher friction than PTFE. For ESD valves, live-loaded packing maintains consistent friction over time but starts at a higher baseline. Always account for packing friction when calculating stroke time, especially for spring-return actuators where the available spring force is limited.
Add a booster relay when the positioner's air delivery capacity cannot fill or exhaust the actuator volume fast enough to meet the required stroke time. Standard positioners deliver 5-15 SCFM, which is adequate for small actuators (under 200 cubic inches) but insufficient for large actuators. A booster relay senses the positioner output and independently supplies or exhausts high-volume air to the actuator. Size the booster relay Cv to deliver the required SCFM at the available supply pressure with acceptable pressure drop. Install the booster as close to the actuator as possible to minimize tubing volume between the booster and actuator.
Disclaimer: This calculator provides valve stroke time estimates for reference purposes. Actual stroke times depend on actuator condition, packing friction, air supply quality, temperature, and installation conditions. ESD valve stroke time requirements must be verified by a qualified safety engineer per IEC 61511 or equivalent standards. ToolGrit is not responsible for valve stroke time, safety system performance, or SIL compliance outcomes.

Learn More

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