Control Valve Diagostics



Control Valve Diagnostics is a modern industrial maintenance tool that can help you prevent deficient or sub-standard performing control valves from entering your mill / plant, determine the operating condition of your control valves and help you identify and resolve valve related problems quickly and efficiently.

Quality conscious valve manufacturers, remanufacturers and repair vendors employ this tool as a way of demonstrating the delivered quality of their valves.

Maintenance departments of reliability conscious valve end-users often use the tool to better understand how their control valve performance has degraded by testing and evaluating their valves at the beginning of each maintenance outage before the valves are removed or repaired.An effective incoming control valve performance inspection program will keep deficient valves fromdelaying outages, reducing productivity and damaging quality.

In both cases, it is important that the valve enduser receive a report that clearly and concisely explains the functional condition of their valves without undue technical jargon or sales bias.

Simply put, many valve diagnostics providers fail in this regard. Some service providers issue a test report, often prepared off-site by someone other than the test technician, that fails to communicate the functional condition effectively. Others may deliver many pages of test data without the summary explanations that turn that pile of paper into the information that the maintenance department needs.

Similarly, many valve end-users are simply unaware of what they should ask for and, in fact, insist on from their diagnostics vendor.

To use this tool effectively and to properly select or supervise a service provider, it is important that the valve end-user understand its basic components and the role they play in assessing valve condition.


Basic Control Valve Diagnostics Tests

Baseline (Dynamic Scan)
Valve Setup
Basic Performance Parameters
Dynamic Tests
Step Response Times
Frequency Response
Accuracy Tests
HDRL (Static Accuracy)
Passive Monitoring of valve
Process Parameters (Optional)
Control Valve Diagnostics

Details Control Valve Diagnostics

Baseline Testing: As the name suggests, this test reports performance parameters that describe the basic setup and condition of the control valve.

  • Travel / Rotation
  • Friction / Torque
  • Hysteresis, Deadband Plus Lag
  • Calibration
  • Benchset / Springrate
  • Seat Load
  • Stroking Smoothness / Anomalies
  • I/P Calibration and Accuracy
  • Positioner Calibration and Control Function
  • Supply Pressure and Flow Adequacy

If these parameters are correct, the valve has a chance of being a good control valve.

Dynamic Testing: As the name suggests, dynamic tests report valve performance with respect to time.

Sensitivity: Determines ability of valve to recognize progressively smaller steps commands when Deadband is not a factor.

Resolution: Determines ability of valve to recognize progressively smaller step commands in opposite directions. The valve must position by crossing the Deadband region.

Step Response Times: Establish stroking times and dynamic response parameters when valve speed is an important factor in valve application.

It is important that steps proceed from large to small. In this way, it is easy to determine when the valve ceases to respond. If stepping is reversed, small to large, early steps may not be recognized. When later steps are recognized, it is not clear what input signal or combination of input signals was responded to.

These parameters are key to a properly functioning control valve. If the valve passes Baseline testing successfully and responds acceptably in these control tests, it is likely to perform properly when installed.

Accuracy Testing: These are conventional calibration tests where the valve is allowed to completely stabilize before a reading is made. Hysteresis, Deadband,
Repeatability and Linearity (HDRL) are the components of static accuracy. Although important is establishing the accuracy of a device, such as I/P transducer, they are not good indicators of a valveā€™s control performance.

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