Full stroke time of the valve

Isn’t it different? There are electric and pneumatic versions! There are also different calibers

From fully closed to fully open and then back to fully closed, or from fully open to fully closed and then back to fully open

Where did this concept come from?

The travel time specified in the petrochemical regulations is very long, so I have some questions

Time for a single stroke. The SH standard is relatively strict. Too fast valves are detrimental to the packing. The control system loop is dynamic, so it is necessary to evaluate the indicators related to the small movements of the valve. It mainly depends on three things: 1. Resolution (the lower, the better). For example, when the input mA changes by 1%, it determines whether the valve can respond accordingly; if it can, then the overall resolution of the valve is 1%. 2. Hysteresis (the lower, the better): For example, when the input mA changes in the opposite direction by 0.5%, should the valve still be able to respond by moving in the opposite direction as well. 3. The response time of the valve (as long as it’s appropriate) – in a temperature control loop, for example, it refers to the time it takes for the valve to reach its desired position after the opening is increased by 2% manually, compared to the time it takes for the temperature to rise to the desired level. The former time should be less than 1/4 of the latter. The valve’s action must be faster than the process response time in order to allow for adjustments to be made. These three points are the most important indicators for evaluating valve performance; refer to GBT 17213.18-2015 Industrial Process Control Valves – Part 9: Test Procedures for Measuring Step Input Response. Using the total travel time to guide design principles is not very reasonable. For example, cylinder actuators have a high acting force and a short full-stroke time, but their performance metrics are inferior to those of spring diaphragms. I won’t prioritize cylinder actuators just to achieve the total travel time required to \"meet specifications\". If you tune the control loop, you will gain a practical understanding of the performance requirements for valves.

You are indeed highly professional. In my humble opinion, the specifications related to petrochemical industries refer to control valves, and the times specified correspond to the time it takes for a control valve to switch from open to closed or from closed to open. It seems that these are mandatory requirements, intended to ensure that the valve can be closed or opened within a specified time once it receives a signal, thereby ensuring safety. The parameters you mentioned seem to apply more to regulating valves. I’m not sure if my understanding is correct; please advise me. Thank you!

You are indeed highly professional. In my humble opinion, the specifications related to petrochemical industries refer to control valves, and the times specified correspond to the time it takes for a control valve to switch from open to closed or from closed to open. It seems that these are mandatory requirements, intended to ensure that the valve can be closed or opened within a specified time once it receives a signal, thereby ensuring safety. The parameters you mentioned seem to apply more to regulating valves. I’m not sure if my understanding is correct; please advise me. Thank you!

This post was last edited by HEJIYUER on 2020-7-21 at 23:15. The operating time of the chain switch valve should be determined based on the time requirements of the entire chain. For example, in the TSHH sequence, the total time required for the process is 5 seconds: 2 seconds for temperature sensing, 1 second for DCS/PLC, and 0.5 seconds for relays. Thus, only 1.5 seconds are left for the valve. The operating time of programmable valves must be designed in accordance with the \"time schedule\" required by the entire process; otherwise, it will not be possible to keep up, as in the case of PSA pressure swing adsorption. 3.5 applies to on-off valves; for example, for a 10-inch valve, 10x3=30s, and the standard range is 10–30s. Overall, we don’t want the time to be too short; rapid movements also have an impact on the pipes. There are likely no specifications requiring the full-stroke time of control valves, as explained in my previous posts. In fact, many intelligent valve positioners combined with upper-level software can be used for dynamic valve testing. For control valves, positioning accuracy and dynamic response are far more important than the \"total stroke time\"; all of these factors serve the process purpose of improving control accuracy and quality.

The following is purely my personal understanding of the work involved: the full-stroke time of valves is only important for stop valves, including both electric and pneumatic ones. The stroke time of a control valve refers to the total time taken to cover the 0%~100% (4~20mA) range of movement; for air-operated valves, this is from fully open (the initial state) to fully closed, while for air-open valves it is from fully closed to fully open. For electric and pneumatic cut-off valves, the stroke depends on whether the valve fault condition is FO or FC? Taking a single-acting FO pneumatic control valve as an example: Fault condition: fully open. Normal operating condition: fully closed. In normal operation, the valve is powered and pressurized; when power or pressure is lost, the valve returns to the fully open position. This is positive action, and the response time is short.