Control Valve Problem

We are facing same problem as you. I think it is the different thermal expansion of material of plug and cage. I think the best way is to consult your control valve vendor and replace suitable plug and cage.

I agree with Mark Jen...what is the temperature range that you require?

phoenix911

Pls. let us know about the process temperature and the temperature range. Then we may give you a workable solution.

Process temperaturte is 230 degc . As per valve date sheet max temp is 430 degc

Hi,

You don´t give information about the actuator, is it a pneumatic one? As the valve malfunction seems occur just when hot, the first idea is temperature is the root cause (maybe differential thermal expansion) either in the valve or the actuator. Valve temperatures must be higher than actuator ones and therefore is the main candidate.

Can you measure the stem thrust, either directly or through diaphragm/piston pressure times the effective area (if pneumatic actuator)?

Can you make a sort of diagnostic test? (it doesn't need a special diagnostic equipment) just some measuring equipment to observe how the actuator performs at hot temperatures.

A check of the measurements against the calculated forces needed to operate the valve in the hot conditions (Delta P, line pressure,...) may help.

Kind regards

You don´t give information about the actuator,

or regulator or the pilot valve, is it stuck or is it a programming issue?

I fully agreed with the comments of KWetz. As per my perception, your controller is giving electrical signal to solenoid valves and the air pressure controll the actuator position. Check the limit of operating air pressure of your actuator. If there is a cussion, please increase the air pressure by adjusting the air regulator. This action will overcome the steam pressure acting on the valve. Actually you have to apply proper force to open or close the valve. In your case valve actuator have not a sufficient force to open more than 50%.

This type of problem we have faced with cage type control valve after opening the valve body, we found that the carbon seal rings were broken.

I think this is the same case with your valve , try changing the spare seal if not than temporarly just to acheive control you can remove the seal assemble the valve without seal and install back but it will not give a tight shut off but it can control the parameter . till you get a spare seal

it iis up to the priority to select