Seek selection guidance for high-temperature water flow control valve
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Dear teachers, the water temperature is 165°C. It is currently controlled by a manual valve, specifically a DN300 manual gate valve; the pipeline diameter is also DN300, with a flow rate of 300 m3/h (at 165°C). The pressure at the pump outlet is 2.2 Mpa, while the pressure behind this gate valve is approximately 1.6 Mpa. For a DN300 manual gate valve, a flow rate of 300 m3/h is achieved even when it is opened only 4 threads – at a temperature of 165°C. Since this manual valve is intended to be replaced with a control valve, what type of valve should be chosen? The diameter of the control valve can be reduced to DN250 or DN200.
For your application scenario, it is recommended to choose a high-temperature water flow control valve. The following factors should be considered when selecting such a valve: 1. Valve material: An alloy material capable of withstanding high temperatures, such as superalloy steel, should be used. 2. Valve type: Control valves should be selected, such as electric control valves or pneumatic control valves. 3. Port size selection: Since your existing pipeline is DN300 with a flow rate of 300 m3/h, and considering the high pressure downstream of the valve, reducing the port size to DN250 or DN200 will enable better control of the flow rate. 4. Pressure rating: The appropriate pressure rating should be selected by taking into account the pressure rating of your existing pipelines, as well as the pressure difference before and after the valve. The final selection should be determined based on your specific requirements and the parameters of the equipment; it is recommended to consult professional valve manufacturers or designers for assistance in making the choice. .
Just provide the specification sheet to the valve manufacturer!
After some calculations, for hot water at high temperatures, a Cv value of 15 is sufficient; a valve with a DN50 diameter will work fine
This post was last edited by pzhmotor on 2023-6-1 17:01. Choose a pneumatic control valve if there is instrument air available; otherwise, choose an electric control valve. (Pneumatic ones are cheaper.) For valve selection, you can download selection guides to make a preliminary choice based on temperature and pressure. Contact the manufacturer’s technical staff again to determine the specific model. (Joint ventures or domestic first- and second-tier brands are all acceptable.) This scenario is similar to that of boiler feed water (the pressure is close to that of low-pressure boilers, and the water temperature is higher). The DN50 valve mentioned above is likely not sufficient; the control valves used for the feed water of 75-ton medium-pressure boilers are DN80 in size. Choose a control valve and add a PID regulator (not necessary if DCS or PLC is available); connect the flow signal to it, and automatic flow control can be implemented (have an electrician handle this to enable both automatic and manual operation).
After recalculation, the Cv value for high-temperature hot water is 143. A DN200 control valve is more than sufficient; the Cv value of a DN150 valve is also adequate, though the flow velocity at the valve outlet is a bit higher. Based on the diameter of your main pipeline, it is recommended to use a DN200 control valve. If access to air supply is available on site, use a pneumatic control valve; if an electric power source is available, use an electric control valve. For the material, 165°C carbon steel WCB is more than sufficient; there is no need to use alloy steel ； From the perspective of operating conditions, a pressure rating of PN40 is sufficient. Your requirements can definitely be met. :)
At a water temperature of 165°C and a flow rate of 300 m3/h (the flow rate at 165°C), the maximum flow rate is already achieved when the gate valve is opened by only 4 threads; therefore, based on these figures, the flow rate adjustment range should be at least 300 m3/h or more. Therefore, it is recommended to use control valves with linear regulation characteristics; the diameter should not be too small. Considering the potential need for some adjustment margin in the future and the high flow rate, control valves with a diameter of DN250 or DN300 are advised. When selecting a control valve, the temperature and pressure of the medium should be taken into account, and materials as well as sealing structures suitable for high-temperature and high-pressure conditions should be chosen. Furthermore, during installation, care must be taken to secure the valve supports and additional pipe supports, in order to avoid issues such as pipe vibration or valve leakage caused by insufficient or unstable supports.