Difference between control valves and pressure reducing valves
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Today, work was being done at the factory to install a control valve on the steam main. However, the construction team asked me for a pressure reducing valve; I said that there was only one control valve indicated in the drawings. The team then kept saying that what they were doing was improper and not standard. I had never heard of the term \"pressure reducing valve\" before; I would like to ask whether there is any relationship between a pressure reducing valve and a control valve. Wouldn’t reducing the opening degree of a control valve also have the effect of lowering pressure? I couldn’t find any information on pressure relief valves on the website; I’m not sure who could provide some details.
This post was last edited by ylb913 on 2015-6-30 at 15:16. The pressure relief valve adjusts the regulating spring inside it according to the required pressure reduction level; once adjusted, it maintains a fixed pressure value. It is a valve that is installed on-site and cannot be controlled from indoors. A control valve can certainly reduce pressure, but it generally requires indoor adjustment; in addition, an indoor pressure indicator is needed for automatic regulation. It depends on what the design provides
On the drawings from the design institute, it is a control valve, specifically a pneumatic diaphragm single-seat control valve
The air supply for the control valve requires a pressure regulator, which can set the instrument air pressure to the level required by the actuator of the control valve.
How could I not know that? When we buy them, they come as a complete set, with the locators already installed
Many steam pipes have a pressure-reducing device where the main pipe meets the branch pipes. It can be a control valve, or a self-acting valve or a steam pressure reducing valve (pressure regulating valve, differential pressure valve). Generally, just one of them is enough.
Composition of the pneumatically controlled valve system: pneumatic actuator + valve + pneumatic-electric positioner + air source treatment unit + manual operating mechanism + silencer + quick-connect fitting. The pressure reducing valve mentioned by the contractor likely refers to the pressure regulator in the air source treatment unit (filter, pressure regulator, oil mister); this is considered a component of the pneumatic valve and should be included when purchasing such a valve. If it isn’t included, ask the valve manufacturer whether it is not required for their type of valve. It’s not necessary either, but it’s possible to include the service life
No, what they need is a steam pressure reducing valve, which is used to lower the pressure of the steam coming from outside to the level required by the system. It’s something similar to a control valve. As for a gas supply triple unit, I’m sure I know about it; I won’t make such a mistake
Oh, I see now. It actually serves the same purpose as a control valve, only one works passively while the other works actively. There’s no need to repeat it
If the pressure in the steam main is much higher than that of the downstream users, a pressure control valve is necessary. The pressure condition valve can be a stand-alone control valve or a conventional control valve; when a conventional control valve is used, a pressure measurement point is provided downstream of the valve, and this value is visible in the PID control system. If it is a pressure-controlled valve on the PID, it is not necessary to install a pressure reducing valve.
May I ask what this pneumatic diaphragm single-seat control valve on site is used to regulate? Pressure? Traffic? Is it the temperature again? If it is used for pressure regulation, then a stand-alone pressure regulator may not be necessary. If it is used for regulating flow rate or temperature, could it be that the pressure before the steam valve in the pipeline is relatively high, while the nominal pressure of the single-seat control valve is relatively low? Another scenario is when pressure needs to be regulated after the control valve – in such cases, the pressure must remain constant with minimal fluctuations. However, if the supply pressure fluctuates greatly, using a single-seat control valve will not ensure good stability of the pressure after it. It’s better to first use a stand-alone pressure regulator to reduce the pressure to a certain level; even if there are fluctuations in this actual pressure, they won’t be too significant compared to the desired set value. Then, a pneumatic single-seat control valve can be used to precisely maintain the pressure after the valve at a constant level...