Issues with control valve parameters
Thread Content
This post was last edited by liu530014416 on 2021-10-20 at 19:58. Dear teachers, a steam cage-type control valve is designed to have a pressure of 20 bar before the valve and 10 bar behind it, with a maximum designed steam flow rate of 10 t/h. Under actual operating conditions, the pressure is 19 bar before the valve and 10 bar behind it, with a maximum steam flow rate of 27 t/h. After 4 months of operation, the valve core shifted from its seat, preventing it from closing; the manufacturer replaced the valve core. It has been running for another 5 months, and now the valve fails to close – it’s basically always open and cannot be closed. Question: What parameters are required to purchase a control valve based on actual operating conditions? How is the CV value calculated, and how can it be determined that newly purchased valves meet the requirements? This is a photo of the new valve core when replacing it.
This post was last edited by hxch150804 on 2021-10-21 08:13. Is this the spool of a cage-type control valve? Angular travel? You should take a close look at the old valve core to determine what is causing it to not close properly. If there is an internal leakage issue, you should consider changing the material of both the valve core and the valve seat. Given the high pressure difference involved, it’s necessary to use materials that are resistant to high temperatures and wear. Also, try to avoid using valves for which it’s difficult to eliminate unbalanced forces.
High-pressure, step-down angle valves should be used; the pressure on both the upstream and downstream sides is already 10 Mpa, so ordinary sleeve or cage types are not sufficient
A cage-type control valve can be used; a labyrinth-style valve cage is chosen to achieve a better elimination of unbalanced forces； Valve body/valve core/valve seat: WCB/304+ST/304+ST. Ask the valve manufacturer to prepare a calculation sheet based on the actual operating conditions
Medium: Steam (saturated steam? Superheated steam? Unsaturated steam? ) Temperature: ? Pressure before the valve: 2 Mpa. Pressure after the valve: 1 Mpa. Medium flow rate: 27 t/h. There are many formulas for calculating the CV value available online; it can be found with just a simple search. As long as all the parameters are provided, newly purchased valves will generally meet the requirements; of course, they need to be products from reputable manufacturers – those from small factories won’t do, and such manufacturers may not even know how to calculate the CV value
Cage valves with this structure are not very good
Ordinary sleeve cages or cage valves are not sufficient; it is recommended to use valve internals with drilling at least at two pressure reduction stages, in order to distribute the flow rate and pressure difference, thereby avoiding severe erosion as well as the problems associated with noise and vibration, and ensuring smoother operation.
This post was last edited by The camellias remain as before on 2021-10-29 at 15:45. The valve selection is incorrect at the moment; a sleeve valve should be used, and there is no need for a valve with multiple pressure reduction stages. A pressure difference of 9 kilograms does not require such multiple stages of pressure reduction – this is for reference only.
The key issue is not the spool, but rather the sleeve design. Voltage reduction series. For communication, 13356746776